Andrew S Cohen
- Professor, Geosciences
- Professor, Ecology and Evolutionary Biology
- Distinguished Professor
- Professor, Global Change - GIDP
- Ph.D. Geology
- University of California-Davis, Davis, California, United States
- Ecological and Paleoecological Aspects of the Rift Valley Lakes of East Africa
- B.A. Joint Geology/Biology
- Middlebury College, Middlebury, Vermont, United States
- Israel Russell Award
- Geological Society of America, Fall 2015
- University of Arizona Distinguished Professor
- University of Arizona, Fall 2014
- University of Arizona Distinguished Professor Award
- University of Arizona, Fall 2014
No activities entered.
Directed ResearchGEOS 492 (Spring 2018)
DissertationGEOS 920 (Spring 2018)
Independent StudyGEOS 399 (Spring 2018)
Master's ReportGEOS 909 (Spring 2018)
Ocean SciencesATMO 412A (Spring 2018)
Ocean SciencesECOL 412A (Spring 2018)
Ocean SciencesENVS 412A (Spring 2018)
Ocean SciencesGEOS 412A (Spring 2018)
Ocean Sciences Field CourseECOL 412B (Spring 2018)
Ocean Sciences Field CourseGEOS 412B (Spring 2018)
DissertationGEOS 920 (Fall 2017)
Independent StudyGEOS 399 (Fall 2017)
Master's ReportGEOS 909 (Fall 2017)
Prin Stratigraphy+SedimGEOS 302 (Fall 2017)
ResearchGEOS 900 (Fall 2017)
Teaching GeosciencesGEOS 397A (Fall 2017)
Topics in GeosciencesGEOS 595A (Fall 2017)
Directed ResearchGEOS 492 (Summer I 2017)
Directed ResearchGEOS 492 (Spring 2017)
DissertationGEOS 920 (Spring 2017)
Honors ThesisGEOS 498H (Spring 2017)
Independent StudyGEOS 499 (Spring 2017)
Paleontol Sediment GeolANTH 596D (Spring 2017)
Paleontol Sediment GeolGEOS 596D (Spring 2017)
Directed ResearchGEOS 392 (Winter 2016)
Directed ResearchGEOS 492 (Fall 2016)
DissertationGEOS 920 (Fall 2016)
Honors ThesisGEOS 498H (Fall 2016)
Prin Stratigraphy+SedimGEOS 302 (Fall 2016)
ResearchGEOS 900 (Fall 2016)
Teaching GeosciencesGEOS 397A (Fall 2016)
- Buatois, L., Labandeira, C., Mangano, M., Cohen, A. S., & Voight, S. (2016). Ch. 11 The Mesozoic Lacustrine Revolution. In The Ichnologic Record of Major Evolutionary Changes(pp 179-263). Springer.
- Cohen, A., McGlue, M., Ellis, G., Zani, H., Swarzenski, P., Assine, M., & Silva, A. (2015). Lake formation, characteristics and evolution in retroarc deposystems: A synthesis of the modern Andean Orogen and its associated basins. In Geodynamics of a Cordilleran Orogenic System: The Central Andes of Argentina and Northern Chile. Geol. Soc. America Memoir 212. doi:10.1130/2015.1212(16)More infoEditors: DeCelles, PG | Ducea, MN | Carrapa, B | Kapp, PA
- McGlue, M., Ellis, G., & Cohen, A. (2015). The modern muds of Laguna Mar Chiquita (Argentina): particle size and organic matter geochemical trends from a large saline lake in the thick-skinned Andean foreland. In Paying Attention to Mudrocks-Priceless(pp 1-18). GSA Special Paper. doi:10.1130/2015.2515(00)
- Campisano, C., Wynn, J., Cohen, A. S., Trauth, M., Arrowsmith, J. R., Stone, J., Asrat, A., Schaebitz, F., Russell, J. L., Behrensmeyer, A. K., Brown, E., Russell, J., Deino, A., Renaut, R., Deocampo, D., Reed, K., Feibel, C., Potts, R., Pelletier, J. D., , Kingston, J., et al. (2017). The Hominin Sites and Paleolakes Drilling Project: Acquiring High-Resolution Paleoclimate Records from the East African Rift System and Their Implications for Understanding the Environmental Context of Hominin Evolution. Paleoanthropology, 2017, 1-43. doi:10.4207/PA.2017.ART104
- Hudson, A. M., Quade, J., Ali, G., Boyle, D., Bassett, S., Huntington, K., De los Santos, M., Cohen, A. S., Lin, K., & Wang, X. (2017). Stable C, O and clumped isotope systematics and 14C geochronology of carbonates from the Quaternary Chewaucan closed-basin lake system, Great Basin, USA: Implications for paleoenvironmental reconstructions using carbonates. Geochimica Cosmochimica Acta, 212, 274-302.
- Ivory, S. J., McGlue, M. M., Ellis, G. S., Boehlke, A., Lezine, A., Vincens, A., & Cohen, A. S. (2017). East African weathering dynamics controlled by vegetation-climate feedbacks. Geology, 45, 823-826.
- Sier, M. J., Langereis, C. G., Dupont-Nivet, G., Feibel, C. S., Joordens, J. C., van der Lubbe, J. H., Beck, C. C., Olago, D. O., Cohen, A. S., & Science Team, W. (2017). The top of the Olduvai Subchron in a high resolution magnetostraitgraphy from the West Turkana core WTK13, Hominin Sites and Paleolakes Drilling Project (HSPDP). Quaternary Geochronology, 42, 117-129.
- Bright, J., Cohen, A. S., Dettman, D. L., Pearthree, P. A., Dorsey, R. J., & Homan, M. (2016). Catastrophic lake spillover integrates the Late Miocene-Pliocene Colorado River and the Gulf of California: Microfaunal and stable isotope evidence from Blythe Basin, California-Arizona, USA. Palaios.
- Cohen, A. S., & Salzburger, W. (2016). Scientific drilling at Lake Tanganyika, Africa: A transformative record for understanding evolution in isolation and the biological history of the African continent, University of Basel, 6-8 June 2016. Scientific Drilling, 2016(4), 1-6.
- Cohen, A. S., Campisano, C., Arrowsmith, R., Asrat, A., Behrensmeyer, A. K., Deino, A., Feibel, C. S., Hill, A., Johnson, R. A., Kingston, J., Lamb, H. F., Lowenstein, T., Noren, A., Olago, D. O., Owen, R. B., Potts, R., Reed, K., Renaut, R., Schabitz, F., , Tiercelin, J., et al. (2016). The Hominin Sites and Paleolakes Drilling Project: Inferring the Environmental Context of Human Evolution from Eastern African Rift Lake Deposits. Scientific Drilling.
- Cohen, A. S., Gergurich, E. L., Kraemer, B. M., McGlue, M. M., McIntyre, P. B., Russell, J. M., Simmons, J. D., & Swarzenski, P. W. (2016). Climate warming reduces fish production and benthic habitat in Lake Tanganyika, one of the most biodiverse freshwater ecosystems. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 113(34), 9563-9568.
- Ivory, S. J., Blome, M. W., King, J. W., McGlue, M. M., Cole, J. E., & Cohen, A. S. (2016). Environmental change explains cichlid adaptive radiation at Lake Malawi over the past 1.2 million years. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 113(42), 11895-11900.
- McGlue, M., Smith, P., Zani, H., Silva, A., Carrapa, B., Cohen, A. S., & Pepper, M. (2016). An integrated sedimentary systems analysis of the Río Bermejo (Argentina): Megafan character in the overfilled southern Chaco Foreland Basin.. Journal of Sedimentary Research, 86, 1359-1377.
- Wright, D., Thompson, J. C., Schilt, F., Cohen, A. S., Choi, J. H., Mercader, J., Nightingale, S., Menzer, S., Walde, D., Welling, M., & Gomani-Chindebvu, E. (2016). Approaches to Middle Stone Age landscape archaeology in tropical Africa. Journal of Archaeological Science.
- Crossey, L. C., Karlstrom, K., Dorsey, R., Pearce, J., Wan, E., Beard, L., Asmerom, Y., Polyak, V., Crow, R. S., Cohen, A. S., Bright, J., & Pecha, M. E. (2015). The importance of groundwater in propagating downward integration of the 6-5Ma Colorado River System: Geochemistry of springs, travertines and lacustrine carbonates of the Grand Canyon region over the past 12 million years. Geosphere, Special Isue CRevolution 2: Origin and Evolution of the Colorado River System II, 660-682.
- DiMaggio, E. N., Arrowsmith, J. R., Campisano, C. J., Johnson, R. A., Deino, A. L., Warren, M., Fisseha, S., & Cohen, A. S. (2015). Tephrostratigraphy and depositional environment of the youngest (< 2.94 Ma) Hadar Formation (southern Afar, Ethiopia). Journal of African Earth Sciences, 112, 234-250.
- DiMaggio, E. N., Arrowsmith, J. R., Campisano, C. J., Johnson, R. A., Deino, A. L., Warren, M., Fisseha, S., & Cohen, A. S. (2015). Tephrostratigraphy and depositional environment of the youngest (< 2.94 Ma) Hadar Formation (southern Afar, Ethiopia). Journal of African Earth Sciences. doi:http://dx.doi.org/10.1016/j.jafrearsci.2015.09.018
- Jackson, L. J., Stone, J. R., Cohen, A. S., & Yost, C. L. (2015). High-resolution paleoecological records from Lake Malawi show no significant cooling associated with the Mount Toba supereruption at ca. 75 ka. GEOLOGY, 43(9), 823-826.
- Lyons, R. P., Scholz, C. A., Cohen, A. S., King, J. W., Brown, E. T., Ivory, S., Johnson, T. C., Deino, A. L., Reinthal, P. N., McGlue, M. M., & Blome, M. W. (2015). A continuous 1.3 million year record of East African hydroclimate, and implications for patterns of evolution and biodiversity. Proceedings of the National Academy of Sciences, 112, 15568-15573. doi:10.1073/pnas.1512864112 PNAS
- McManus, J., Severmann, S., Cohen, A., McKay, J., Brucker, R. P., Wheatcroft, R., Hartwell, A. M., & Montayne, B. R. (2015). The sedimentary response to a rapid change in lake level in Lake Tanganyika. Palaeogeography, Palaeoclimatology, Palaeoecology, 440, 647-658.
- Wynn, J., Trauth, M., Stone, J., Schaebitz, F., Russell, J. L., Russell, J., Renaut, R., Reed, K., Potts, R., Pelletier, J. D., Owen, R. B., Olago, D., Noren, A., Lowenstein, T., Lamb, H., Kingston, J., Feibel, C., Deocampo, D., Deino, A., , Brown, E., et al. (2017). The Hominin Sites and Paleolakes Drilling Project: Acquiring High-Resolution Paleoclimate Records from the East African Rift System and Their Implications for Understanding the Environmental Context of Hominin Evolution. Paleoanthropology, 2017, 1-43. doi:doi: 10.4207/PA.2017.ART104More infoThe possibility of a causal relationship between Earth history processes and hominin evolution in Africa has been the subject of intensive paleoanthropological research for the last 25 years. One fundamental question is: can any geohistorical processes, in particular, climatic ones, be characterized with sufficient precision to enable temporal correlation with events in hominin evolution and provide support for a possible causal mechanism for evolutionary changes? Previous attempts to link paleoclimate and hominin evolution have centered on evidence from the outcrops where the hominin fossils are found, as understanding whether and how hominin populations responded to habitat change must be examined at the local basinal scale. However, these outcrop records typically provide incomplete, low-resolution climate and environmental histories, and surface weathering often precludes the application of highly sensitive, state-of-the-art paleoenvironmental methods. Continuous and well-preserved deep-sea drill core records have provided an alternative approach to reconstructing the context of hominin evolution, but have been collected at great distances from hominin sites and typically integrate information over vast spatial scales. The goal of the Hominin Sites and Paleolakes Drilling Project (HSPDP) is to analyze climate and other Earth system dynamics using detailed paleoenvironmental data acquired through scientific drilling of lacustrine depocenters at or near six key paleoanthropological sites in Kenya and Ethiopia. This review provides an overview of a unique collaboration of paleoanthropologists and earth scientists who have joined together to explicitly explore key hypotheses linking environmental history and mammalian (including hominin) evolution and potentially develop new testable hypotheses. With a focus on continuous, high-resolution proxies at timescales relevant to both biological and cultural evolution, the HSPDP aims to dramatically expand our understanding of the environmental history of eastern Africa during a significant portion of the Late Neogene and Quaternary, and to generate useful models of long-term environmental dynamics in the region.
- Blome, M., Cohen, A., & Lopez, M. (2014). Modern distribution of ostracodes and other limnological indicators in southern Lake Malawi: Implications for paleoecological studies. Hydrobiologia.More infoDOI: 10.1007/s10750-014-1817-5
- Ivory, S. J., McGlue, M. M., Ellis, G. S., Lezine, A., Cohen, A. S., & Vincens, A. (2014). Vegetation Controls on Weathering Intensity during the Last Deglacial Transition in Southeast Africa. PLOS ONE, 9(11).
- Odigie, K. O., Cohen, A. S., Swarzenski, P. W., & Flegal, A. R. (2014). Using lead isotopes and trace element records from two contrasting Lake Tanganyika sediment cores to assess watershed - Lake exchange. APPLIED GEOCHEMISTRY, 51, 184-190.
- Odigie, K., Cohen, A., Swarzenski, P., & Fleagal, A. (2014). Using lead isotopes and trace element records from two contrasting Lake Tanganyika sediment cores to assess watershed-lake exchange. Applied Geochemistry, 51, 184-190.
- Salzburger, W., Van, B. B., & Cohen, A. S. (2014). Ecology and Evolution of the African Great Lakes and Their Faunas. ANNUAL REVIEW OF ECOLOGY, EVOLUTION, AND SYSTEMATICS, VOL 45, 45, 519-+.
- Salzburger, W., VanBocxlaer, B., & Cohen, A. S. (2014). The ecology and evolution of the African Great Lakes and their faunas. Annual Reviews of Ecology, Evolution and Systematics, 45, 519-546.
- Wright, D. K., Thompson, J., Mackay, A., Welling, M., Forman, S. L., Price, G., Zhao, J., Cohen, A. S., Malijani, O., & Gomani-Chindebvu, E. (2014). Renewed Geoarchaeological Investigations of Mwanganda's Village (Elephant Butchery Site), Karonga, Malawi. GEOARCHAEOLOGY-AN INTERNATIONAL JOURNAL, 29(2), 98-120.
- Wright, D. K., Thompson, J., Mackay, A., Welling, M., Forman, S. L., Price, G., Zhao, J., Cohen, A. S., Malijani, O., & Gomani-Chindebvu, E. (2014). Renewed Geoarchaeological Investigations of Mwanganda's Village (Elephant Butchery Site), Karonga, Malawi. Geoarchaeology, 29(2), 98-120.More infoAbstract: The site of Mwanganda's Village, located along a paleochannel in northern Malawi, is one of only a few sites that have characterized the Middle Stone Age (MSA) of Malawi for decades (Clark & Haynes, ; Clark et al., ; Kaufulu, ). The Malawi Earlier-Middle Stone Age Project has re-examined the site using new mapping and chronometric tools in order to reinterpret the site's significance within the context of current debates surrounding human origins and the potential role the environment played in shaping human behavior. The new data do not support the previous hypothesis that the site was an elephant butchery location (contra Clark & Haynes, ; Clark et al., ; Kaufulu, ). Instead, the evidence shows successive colonization of riparian corridors by MSA hunter-gatherers focused on exploiting localized resources during periods of generally humid climates while other lakes desiccated across Africa. We challenge the hypothesis that stable and intermediately high lake levels within the African Rift Valley System (sensu Trauth et al., ) catalyzed the evolution of regional interaction networks between 42 and 22 ka. Instead, we interpret the evidence to suggest that regional variants of technology persist into the late MSA as foragers focused on exploiting resources from local catchments. © 2014 Wiley Periodicals, Inc.
- Cohen, A. S., Bocxlaer, B. V., Todd, J. A., McGlue, M., Michel, E., Nkotagu, H. H., Grove, A. T., & Delvaux, D. (2013). Quaternary ostracodes and molluscs from the Rukwa Basin (Tanzania) and their evolutionary and paleobiogeographic implications. Palaeogeography, Palaeoclimatology, Palaeoecology, 392, 79-97.More infoAbstract: Much of the spectacular biodiversity of the African Great Lakes is endemic to single lake basins so that the margins of these basins or their lakes coincide with biogeographic boundaries. Longstanding debate surrounds the evolution of these endemic species, the stability of bioprovinces, and the exchange of faunas between them over geologic time as the rift developed. Because these debates are currently unsettled, we are uncertain of how much existing distribution patterns are determined by modern hydrological barriers versus reflecting past history. This study reports on late Quaternary fossils from the Rukwa Basin and integrates geological and paleoecological data to explore faunal exchange between freshwater bioprovinces, in particular with Lake Tanganyika. Lake Rukwa's water level showed large fluctuations over the last 25. ky, and for most of this period the lake contained large habitat diversity, with different species assemblages and taphonomic controls along its northern and southern shores. Comparison of fossil and modern invertebrate assemblages suggests faunal persistence through the Last Glacial Maximum, but with an extirpation event that occurred in the last 5. ky. Some of the molluscs and ostracodes studied here are closely related to taxa (or part of clades) that are currently endemic to Lake Tanganyika, but others testify to wider and perhaps older faunal exchanges between the Rukwa bioprovince and those of Lake Malawi and the Upper Congo (in particular Lake Mweru). The Rukwa Basin has a long history of rifting and lacustrine conditions and, at least temporarily, its ecosystems appear to have functioned as satellites to Lake Tanganyika in which intralacustrine speciation occurred. Paleontological studies of the Rukwa faunas are particularly relevant because of the basin's important role in the late Cenozoic biogeography of tropical Africa, and because many of the molecular traces potentially revealing this history would have been erased in the late Holocene extirpation.© 2013 Elsevier B.V.
- Cohen, A. S., Van, B. B., Todd, J. A., McGlue, M., Michel, E., Nkotagu, H. H., Grove, A. T., & Delvaux, D. (2013). Quaternary ostracodes and molluscs from the Rukwa Basin (Tanzania) and their evolutionary and paleobiogeographic implications. PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY, 392, 79-97.
- Ivory, S. J., Russell, J. L., & Cohen, A. S. (2013). In the hot seat: Insolation, ENSO, and vegetation in the African tropics. Journal of Geophysical Research – Biogeosciences, 118, 1347-1358.More infoAbstract African climate is changing at rates unprecedented in the Late Holocene with profound implications for tropical ecosystems and the global hydrologic cycle. Understanding the specific climate drivers behind tropical ecosystem change is critical for both future and paleomodeling efforts. However, linkages between climate and vegetation in the tropics have been extremely controversial. The Normalized Difference Vegetation Index (NDVI) is a satellite-derived index of vegetation productivity with a high spatial and temporal resolution. Here we use regression analysis to show that NDVI variability in Africa is primarily correlated with the interannual extent of the Intertropical Convergence Zone (ITCZ). Our results indicate that interannual variability of the ITCZ, rather than sea surface temperatures or teleconnections to middle/high latitudes, drives patterns in African vegetation resulting from the effects of insolation anomalies and El Niño–Southern Oscillation (ENSO) events on atmospheric circulation. Global controls on tropical atmospheric circulation allow for spatially coherent reconstruction of interannual vegetation variability throughout Africa on many time scales through regulation of dry season length and moisture convergence, rather than precipitation amount.
- Ivory, S. J., Russell, J., & Cohen, A. S. (2013). In the hot seat: Insolation, ENSO, and vegetation in the african tropics. Journal of Geophysical Research G: Biogeosciences, 118(4), 1347-1358.More infoAbstract: African climate is changing at rates unprecedented in the Late Holocene with profound implications for tropical ecosystems and the global hydrologic cycle. Understanding the specific climate drivers behind tropical ecosystem change is critical for both future and paleomodeling efforts. However, linkages between climate and vegetation in the tropics have been extremely controversial. The Normalized Difference Vegetation Index (NDVI) is a satellite-derived index of vegetation productivity with a high spatial and temporal resolution. Here we use regression analysis to show that NDVI variability in Africa is primarily correlated with the interannual extent of the Intertropical Convergence Zone (ITCZ). Our results indicate that interannual variability of the ITCZ, rather than sea surface temperatures or teleconnections to middle/high latitudes, drives patterns in African vegetation resulting from the effects of insolation anomalies and El Niño-Southern Oscillation (ENSO) events on atmospheric circulation. Global controls on tropical atmospheric circulation allow for spatially coherent reconstruction of interannual vegetation variability throughout Africa on many time scales through regulation of dry season length and moisture convergence, rather than precipitation amount. Key Points Atmospheric variability has a dramatic effect on tropical African vegetation. ITCZ position and intensity result from variations in insolation and ENSO. Growing season vegetation controls are both rainfall and dry season length. ©2013. American Geophysical Union. All Rights Reserved.
- McGlue, M. M., Cohen, A. S., Ellis, G. S., & Kowler, A. L. (2013). Late Quaternary stratigraphy, sedimentology and geochemistry of an underfilled lake basin in the Puna plateau (northwest Argentina). BASIN RESEARCH, 25(6), 638-658.
- Mcglue, M. M., Cohen, A. S., Ellis, G. S., & Kowler, A. L. (2013). Late Quaternary stratigraphy, sedimentology and geochemistry of an underfilled lake basin in the Puna plateau (northwest Argentina). Basin Research, 25(6), 638-658.More infoAbstract: Depositional models of ancient lakes in thin-skinned retroarc foreland basins rarely benefit from appropriate Quaternary analogues. To address this, we present new stratigraphic, sedimentological and geochemical analyses of four radiocarbon-dated sediment cores from the Pozuelos Basin (PB; northwest Argentina) that capture the evolution of this low-accommodation Puna basin over the past ca. 43 cal kyr. Strata from the PB are interpreted as accumulations of a highly variable, underfilled lake system represented by lake-plain/littoral, profundal, palustrine, saline lake and playa facies associations. The vertical stacking of facies is asymmetric, with transgressive and thin organic-rich highstand deposits underlying thicker, organic-poor regressive deposits. The major controls on depositional architecture and basin palaeogeography are tectonics and climate. Accommodation space was derived from piggyback basin-forming flexural subsidence and Miocene-Quaternary normal faulting associated with incorporation of the basin into the Andean hinterland. Sediment and water supply was modulated by variability in the South American summer monsoon, and perennial lake deposits correlate in time with several well-known late Pleistocene wet periods on the Altiplano/Puna plateau. Our results shed new light on lake expansion-contraction dynamics in the PB in particular and provide a deeper understanding of Puna basin lakes in general. Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.
- Blome, M. W., Cohen, A. S., Tryon, C. A., Brooks, A. S., & Russell, J. (2012). The environmental context for the origins of modern human diversity: A synthesis of regional variability in African climate 150,000-30,000 years ago. JOURNAL OF HUMAN EVOLUTION, 62(5), 563-592.
- Blome, M. W., Cohen, A. S., Tryon, C. A., Brooks, A. S., & Russell, J. (2012). The environmental context for the origins of modern human diversity: A synthesis of regional variability in African climate 150,000-30,000 years ago. Journal of Human Evolution, 62(5), 563-592.More infoPMID: 22513381;Abstract: We synthesize African paleoclimate from 150 to 30 ka (thousand years ago) using 85 diverse datasets at a regional scale, testing for coherence with North Atlantic glacial/interglacial phases and northern and southern hemisphere insolation cycles. Two major determinants of circum-African climate variability over this time period are supported by principal components analysis: North Atlantic sea surface temperature (SST) variations and local insolation maxima. North Atlantic SSTs correlated with the variability found in most circum-African SST records, whereas the variability of the majority of terrestrial temperature and precipitation records is explained by local insolation maxima, particularly at times when solar radiation was intense and highly variable (e.g., 150-75 ka). We demonstrate that climates varied with latitude, such that periods of relatively increased aridity or humidity were asynchronous across the northern, eastern, tropical and southern portions of Africa. Comparisons of the archaeological, fossil, or genetic records with generalized patterns of environmental change based solely on northern hemisphere glacial/interglacial cycles are therefore imprecise.We compare our refined climatic framework to a database of 64 radiometrically-dated paleoanthropological sites to test hypotheses of demographic response to climatic change among African hominin populations during the 150-30 ka interval. We argue that at a continental scale, population and climate changes were asynchronous and likely occurred under different regimes of climate forcing, creating alternating opportunities for migration into adjacent regions. Our results suggest little relation between large scale demographic and climate change in southern Africa during this time span, but strongly support the hypothesis of hominin occupation of the Sahara during discrete humid intervals ~135-115 ka and 105-75 ka. Hominin populations in equatorial and eastern Africa may have been buffered from the extremes of climate change by locally steep altitudinal and rainfall gradients and the complex and variable effects of increased aridity on human habitat suitability in the tropics. Our data are consistent with hominin migrations out of Africa through varying exit points from ~140-80 ka. © 2012 Elsevier Ltd.
- Cohen, A. S. (2012). Scientific drilling and biological evolution in ancient lakes: Lessons learned and recommendations for the future. Hydrobiologia, 682(1), 3-25.More infoAbstract: Scientific drilling to recover sediment core and fossil samples is a promising approach to increasing our understanding of species evolution in ancient lakes. Most lake drilling efforts to date have focused on paleoclimate reconstruction. However, it is clear from the excellent fossil preservation and high temporal resolution typical of lake beds that significant advances in evolutionary biology can be made through drill core studies coordinated with phylogenetic work on appropriate taxa. Geological records can be used to constrain the age of specific lakes and the timing of evolutionarily significant events (such as lake level fluctuations and salinity crises). Fossil data can be used to test speciation and biogeographic hypotheses and flesh out phylogenetic trees, using a better-resolved fossil record to estimate timing of phylogenetic divergences. The extraordinary preservation of many fossils in anoxic lake beds holds the hope of collecting fossil DNA from the same body fossils that improve our understanding of morphological character evolution and adaptation. Moreover, fossils allow calibration of molecular clocks, which are currently largely inferential. Lake Malawi Drilling Project results provide some guideposts on what might be expected in a drilling project for studies of evolution. The extreme variability in lake level and environmental history that most ancient lakes experience (exemplified by the Lake Malawi record) demonstrates that no one drilling locality is likely to provide a complete record of phylogenetic history for a radiating lineage. Evolutionary biologists should take an active role in the design of drilling projects, which typically have interdisciplinary objectives, to ensure their sampling needs will be met by whatever sites in a lake are ultimately drilled. © 2011 Springer Science+Business Media B.V.
- Conaway, C. H., Swarzenski, P. W., & Cohen, A. S. (2012). Recent paleorecords document rising mercury contamination in Lake Tanganyika. APPLIED GEOCHEMISTRY, 27(1), 352-359.
- Conaway, C. H., Swarzenski, P. W., & Cohen, A. S. (2012). Recent paleorecords document rising mercury contamination in Lake Tanganyika. Applied Geochemistry, 27(1), 352-359.More infoAbstract: Recent Lake Tanganyika Hg deposition records were derived using 14C and excess 210Pb geochronometers in sediment cores collected from two contrasting depositional environments: the Kalya Platform, located mid-lake and more removed from watershed impacts, and the Nyasanga/Kahama River delta region, located close to the lake's shoreline north of Kigoma. At the Kalya Platform area, pre-industrial Hg concentrations are 23±0.2ng/g, increasing to 74ng/g in modern surface sediment, and the Hg accumulation rate has increased from 1.0 to 7.2μg/m 2/a from pre-industrial to present, which overall represents a 6-fold increase in Hg concentration and accumulation. At the Nyasanga/Kahama delta region, pre-industrial Hg concentrations are 20±3ng/g, increasing to 46ng/g in surface sediment. Mercury accumulation rate has increased from 30 to 70μg/m 2/a at this site, representing a 2-3-fold increase in Hg concentration and accumulation. There is a lack of correlation between charcoal abundance and Hg accumulation rate in the sediment cores, demonstrating that local biomass burning has little relationship with the observed Hg concentration or Hg accumulation rates. Examined using a sediment focusing-corrected mass accumulation rate approach, the cores have similar anthropogenic atmospheric Hg deposition profiles, suggesting that after accounting for background sediment concentrations the source of accumulating Hg is predominantly atmospheric in origin. In summary, the data document an increase of Hg flux to the Lake Tanganyika ecosystem that is consistent with increasing watershed sediment delivery with background-level Hg contamination, and regional as well as global increases in atmospheric Hg deposition. © 2011.
- Ivory, S. J., Lezine, A., Vincens, A., & Cohen, A. S. (2012). Effect of aridity and rainfall seasonality on vegetation in the southern tropics of East Africa during the Pleistocene/Holocene transition. QUATERNARY RESEARCH, 77(1), 77-86.
- Ivory, S. J., Lézine, A., Vincens, A., & Cohen, A. S. (2012). Effect of aridity and rainfall seasonality on vegetation in the southern tropics of East Africa during the Pleistocene/Holocene transition. Quaternary Research, 77(1), 77-86.More infoAbstract: Fossil pollen analyses from northern Lake Malawi, southeast Africa, provide a high-resolution record of vegetation change during the Pleistocene/Holocene transition (~. 18-9. ka). Recent studies of local vegetation from lowland sites have reported contrasting rainfall signals during the Younger Dryas (YD). The Lake Malawi record tracks regional vegetation changes and allows comparison with other tropical African records identifying vegetation opening and local forest maintenance during the YD. Our record shows a gradual decline of afromontane vegetation at 18. ka. Around 14.5. ka, tropical seasonal forest and Zambezian miombo woodland became established. At ~. 13. ka, drier, more open formations gradually became prevalent. Although tropical seasonal forest taxa were still present in the watershed during the YD, this drought-intolerant forest type was likely restricted to areas of favorable edaphic conditions along permanent waterways. The establishment of drought-tolerant vegetation followed the reinforcement of southeasterly tradewinds resulting in a more pronounced dry winter season after ~. 11.8. ka. The onset of the driest, most open vegetation type was coincident with a lake low stand at the beginning of the Holocene. This study demonstrates the importance of global climate forcing and local geomorphological conditions in controlling vegetation distribution. © 2011 University of Washington.
- McGlue, M. M., Silva, A., Corradini, F. A., Zani, H., Trees, M. A., Ellis, G. S., Parolin, M., Swarzenski, P. W., Cohen, A. S., & Assine, M. L. (2012). Erratum to: Limnogeology in Brazil's "forgotten wilderness": A synthesis from the large floodplain lakes of the Pantanal (J Paleolimnol (2011), 46, (273-289), 10.1007/s10933-011-95380-5). Journal of Paleolimnology, 47(1), 165-166.
- McGlue, M. M., Silva, A., Zani, H., Corradini, F. A., Parolin, M., Abel, E. J., Cohen, A. S., Assine, M. L., Ellis, G. S., Trees, M. A., Kuerten, S., Gradella, F., & Rasbold, G. G. (2012). Lacustrine records of Holocene flood pulse dynamics in the Upper Paraguay River watershed (Pantanal wetlands, Brazil). QUATERNARY RESEARCH, 78(2), 285-294.
- McGlue, M. M., Silva, A., Zani, H., Corradini, F. A., Parolin, M., Abel, E. J., Cohen, A. S., Assine, M. L., Ellis, G. S., Trees, M. A., Kuerten, S., dos, F., & Rasbold, G. G. (2012). Lacustrine records of Holocene flood pulse dynamics in the Upper Paraguay River watershed (Pantanal wetlands, Brazil). Quaternary Research (United States), 78(2), 285-294.More infoAbstract: The Pantanal is the world's largest tropical wetland and a biodiversity hotspot, yet its response to Quaternary environmental change is unclear. To address this problem, sediment cores from shallow lakes connected to the Upper Paraguay River (PR) were analyzed and radiocarbon dated to track changes in sedimentary environments. Stratal relations, detrital particle size, multiple biogeochemical indicators, and sponge spicules suggest fluctuating lake-level lowstand conditions between ~11,000 and 5300. cal. yr BP, punctuated by sporadic and in some cases erosive flood flows. A hiatus has been recorded from ~5300 to 2600. cal. yr BP, spurred by confinement of the PR within its channel during an episode of profound regional drought. Sustained PR flooding caused a transgression after ~2600. cal. yr BP, with lake-level highstand conditions appearing during the Little Ice Age. Holocene PR flood pulse dynamics are best explained by variability in effective precipitation, likely driven by insolation and tropical sea-surface temperature gradients. Our results provide novel support for hypotheses on: (1) stratigraphic discontinuity of floodplain sedimentary archives; (2) late Holocene methane flux from Southern Hemisphere wetlands; and (3) pre-colonial indigenous ceramics traditions in western Brazil. © 2012.
- Mcglue, M. M., Ellis, G. S., Cohen, A. S., & Swarzenski, P. W. (2012). Playa-lake sedimentation and organic matter accumulation in an Andean piggyback basin: The recent record from the Cuenca de Pozuelos, North-west Argentina. Sedimentology, 59(4), 1237-1256.More infoAbstract: Expansive playa-lake systems situated in high-altitude piggyback basins are important and conspicuous components of both modern and ancient cordilleran orogenic systems. Extant playa lakes provide vital habitat for numerous endemic species, whereas sediments from these deposystems may record signals of climate change or develop natural resources over geological time. Laguna de los Pozuelos (North-west Argentina) provides the opportunity for an actualistic sedimentological and geochemical assessment of a piggyback basin playa lake in an area of critical interest for understanding Quaternary palaeoclimate dynamics. Silty clays and diatom ooze are the dominant playa-lake centre microfacies, with concentrations of total organic carbon and biogenic silica commonly exceeding 1·5wt% in this sub-environment. Elemental and stable isotopic analyses point to a mixed organic matter composition in the playa-lake centre, with substantial contributions from algae and transported aquatic macrophytes. Bulk sediment and organic mass accumulation rates in the southern playa-lake centre approach 0·22gcm -2year -1 and 2·89mgcm -2year -1, respectively, indicating moderately rapid deposition with negligible deflation over historic time. Playa margin facies contain higher percentages of fragmented biogenic carbonate (ostracods and charophytes) and inorganically precipitated aragonite crusts due to seasonal pumping and evaporation of ground water. Organic matter accumulation is limited along these heavily bioturbated wet and dry mud flats. Fluvial-lacustrine transitional environments, which are key waterbird habitats, are either silty terminal splay (northern axis) or sandy deltas (southern axis) containing highly oxidized and partially allochthonous organic matter. Modern analogue data from Laguna de los Pozuelos provide key insights for: (i) environmental reconstructions of ancient lake sequences; and (ii) improving facies models for piggyback basins. © 2011 The Authors. Journal compilation © 2011 International Association of Sedimentologists.
- Mcglue, M. M., Ellis, G. S., Cohen, A. S., & Swarzenski, P. W. (2012). Playa-lake sedimentation and organic matter accumulation in an Andean piggyback basin: the recent record from the Cuenca de Pozuelos, North-west Argentina. SEDIMENTOLOGY, 59(4), 1237-1256.
- Russell, J. M., Cohen, A. S., Johnson, T. C., & Scholz, C. A. (2012). Scientific drilling in the East African rift lakes: A strategic planning workshop. Scientific Drilling, 49-54.
- Beuning, K. R., Zimmerman, K. A., Ivory, S. J., & Cohen, A. S. (2011). Vegetation response to glacial-interglacial climate variability near Lake Malawi in the southern African tropics. Palaeogeography, Palaeoclimatology, Palaeoecology, 303(1-4), 81-92.More infoAbstract: Pollen records from Lake Malawi, Africa spanning the last 135kyr show substantial and abrupt vegetation response to multiple episodes of extreme aridity between 135 and 75ka. Peaks in both the relative abundance and total production of Podocarpus pollen define the first two of these drought episodes. From 135 to 127 and again from 117 to 105kyr BP, Podocarpus percentages remain above 16% with peak values as high as 38% indicating a period marked by a cool climate resulting in expansion of montane forest taxa to lower elevations. Marine palynological records from the Angola Margin and Congo Fan show similar peak Podocarpus percentages at this time (oxygen isotope stage 5d) indicating a similar climate across the African continent at this latitude. From 105 to 90ka, continuing drought resulted in total pollen accumulation rates in Lake Malawi to fall to less than 300grains/cm2/yr of predominately grass pollen. This episode in African history was severe enough to cause the disappearance of pteridophytes and forest taxa such as Uapaca and Brachystegia as well as montane taxa (Podocarpus, Olea spp. and Ericaceae) within the pollen source area of Lake Malawi. These taxa all remain nearly absent from the surrounding vegetation for the next 18,000years. The resultant semi-desert vegetation would have been inhospitable for early humans living within or traveling through the Lake Malawi region. Increasing moisture following these arid intervals allowed expansion, creation and maintenance of a more diverse landscape vegetation mosaic around Lake Malawi including Zambezian miombo woodland, humid evergreen woodland and afromontane forests. The relative abundance of each fluctuated in response to either cooling (i.e. afromontane expansion from 60 to 56ka) or moisture balance (i.e. increasing humid evergreen woodland between 75 and 65ka). Notably there was no significant change in vegetation composition during the Last Glacial Maximum (LGM) (30-15ka) as compared to the previous 20,000years. © 2010 Elsevier B.V.
- McGlue, M. M., Silva, A., Corradini, F. A., Zani, H., Trees, M. A., Ellis, G. S., Parolin, M., Swarzenski, P. W., Cohen, A. S., & Assine, M. L. (2011). Limnogeology in Brazil's "forgotten wilderness": A synthesis from the large floodplain lakes of the Pantanal. Journal of Paleolimnology, 46(2), 273-289.More infoAbstract: Sediment records from floodplain lakes have a large and commonly untapped potential for inferring wetland response to global change. The Brazilian Pantanal is a vast, seasonally inundated savanna floodplain system controlled by the flood pulse of the Upper Paraguay River. Little is known, however, about how floodplain lakes within the Pantanal act as sedimentary basins, or what influence hydroclimatic variables exert on limnogeological processes. This knowledge gap was addressed through an actualistic analysis of three large, shallow ( Si4+ > Ca2+), mildly alkaline, freshwater systems, the chemistries and morphometrics of which evolve with seasonal flooding. Lake sills are bathymetric shoals marked by siliciclastic fans and marsh vegetation. Flows at the sills likely undergo seasonal reversals with the changing stage of the Upper Paraguay River. Deposition in deeper waters, typically encountered in proximity to margin-coincident topography, is dominated by reduced silty-clays with abundant siliceous microfossils and organic matter. Stable isotopes of carbon and nitrogen, plus hydrogen index measured on bulk organic matter, suggest that contributions from algae (including cyanobacteria) and other C3-vegetation dominate in these environments. The presence of lotic sponge spicules, together with patterns of terrigenous sand deposition and geochemical indicators of productivity, points to the importance of the flood pulse for sediment and nutrient delivery to the lakes. Flood-pulse plumes, waves and bioturbation likewise affect the continuity of sedimentation. Short-lived radioisotopes indicate rates of 0.11-0.24 cm year-1 at sites of uninterrupted deposition. A conceptual facies model, developed from insights gained from modern seasonal processes, can be used to predict limnogeological change when the lakes become isolated on the floodplain or during intervals associated with a strengthened flood pulse. Amplification of the seasonal cycle over longer time scales suggests carbonate, sandy lowstand fan and terrestrial organic matter deposition during arid periods, whereas deposition of lotic sponges, mixed aquatic organic matter, and highstand deltas characterizes wet intervals. The results hold substantial value for interpreting paleolimnological records from floodplain lakes linked to large tropical rivers with annual flooding cycles. © 2011 Springer Science+Business Media B.V.
- McGlue, M. M., Silva, A., Corradini, F. A., Zani, H., Trees, M. A., Ellis, G. S., Parolin, M., Swarzenski, P. W., Cohen, A. S., & Assine, M. L. (2011). Limnogeology in Brazil's "forgotten wilderness": a synthesis from the large floodplain lakes of the Pantanal. JOURNAL OF PALEOLIMNOLOGY, 46(2), 273-289.
- McHargue, L. R., Jull, A. J., & Cohen, A. (2011). Measurement of 10Be from Lake Malawi (Africa) drill core sediments and implications for geochronology. Palaeogeography, Palaeoclimatology, Palaeoecology, 303(1-4), 110-119.More infoAbstract: The cosmogenic radionuclide 10Be was measured from drill core sediments from Lake Malawi in order to help construct a chronology for the study of the tropical paleoclimate in East Africa. Sediment samples were taken every 10m from the core MAL05-1C to 80m in depth and then from that depth in core MAL05-1B to 382m. Sediment samples were then later taken at a higher resolution of every 2m from MAL05-1C. They were then leached to remove the authigenic fraction, the leachate was processed to separate out the beryllium isotopes, and 10Be was measured at the TAMS Facility at the University of Arizona. The 10Be/9Be profile from Lake Malawi sediments is similar to those derived from marine sediment cores for the late Pleistocene, and is consistent with the few radiocarbon and OSL IR measurements made from the same core. Nevertheless, a strong correlation between the stable isotope 9Be and the cosmogenic isotope 10Be suggests that both isotopes have been well mixed before deposition unlike in some marine sediment cores. In addition, the correlation of beryllium isotopes to a proxy of lake level TOC (Total Organic Matter) from Lake Malawi indicates that the concentrations of 10Be in the lake sediments result from the combined effects of global and local climates on lake level, local hydrology, and sediment transport in the Lake Malawi basin rather than as a direct response to its production in the atmosphere modulated by the intensity of the Earth's dipole. Therefore, a direct correlation of the 10Be/9Be to a chronology derived from the paleomagnetic variations measured from marine sediments was not possible. Nevertheless, a comparison of the 10Be/9Be chronology, allowing for decay, at Lake Malawi to that of the global marine paleomagnetic record suggests that the bottom of core MAL05-1B is no more than 750ka in age. © 2010.
- Park, L. E., & Cohen, A. S. (2011). Paleoecological response of ostracods to early Late Pleistocene lake-level changes in Lake Malawi, East Africa. PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY, 303(1-4), 71-80.
- Park, L. E., & Cohen, A. S. (2011). Paleoecological response of ostracods to early Late Pleistocene lake-level changes in Lake Malawi, East Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 303(1-4), 71-80.More infoAbstract: Ostracod species from at least seven genera were recovered from drill cores recently collected at Lake Malawi, a large (29,500km2) and deep (706m) African rift valley lake located in the southern African tropics (9-14° S). These genera include Limnocythere, Candonopsis, Ilyocypris, Sclerocypris, Gomphocythere, possible Allocypria? and an unknown Cypridosine. Taphonomic variables such as the percentage of valve breakage, adult individuals, carbonate and oxidized coatings as well as associated mineralogy, can be used to delineate lake-level low and highstands. This record of lake-level fluctuations is correlated with paleoecological changes in ostracod communities throughout the core record of the past ~145ka. Two major assemblages found within the Lake Malawi cores include a Limnocythere-dominated shallow, saline/alkaline assemblage that occurred between 133 and 130ka and between 118 and 90ka and a deeper water Cypridopsine assemblage that lived in waters 10s to 100s of meters in depth and dominated the ostracod assemblage during intervals of lake-level transitions (136-133ka, 129-128ka and 86-63ka), between the occurrence of the littoral assemblage and the appearance of indicators of bottom water anoxia. Changes in occurrences and abundances indicate variations in paleoecological affinities related to lake chemistry and oxygenation of bottom waters. The characteristics of the different lineages influence how that lineage is likely to respond to environmental variability such as lake-level fluctuations. Clades that include large numbers of endemic species in Lake Malawi tend to be specialists and thus more susceptible to environmental perturbations. On the other hand, cosmopolitan species within the lake all appear to be generalists, suggesting that they have high tolerances to environmental variability and therefore, these genera tend to be monospecific within the lake and are less likely to have radiated within the basin. The distribution of these ostracods can be used to evaluate hypotheses about the environmental history at the landscape-scale and their potential influence on species' distribution and diversification histories. © 2010 Elsevier B.V.
- Reinthal, P. N., Cohen, A. S., & Dettman, D. L. (2011). Fish fossils as paleo-indicators of ichthyofauna composition and climatic change in Lake Malawi, Africa. PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY, 303(1-4), 126-132.
- Reinthal, P. N., Cohen, A. S., & Dettman, D. L. (2011). Fish fossils as paleo-indicators of ichthyofauna composition and climatic change in Lake Malawi, Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 303(1-4), 126-132.More infoAbstract: Numerous biological and chemical paleorecords have been used to infer paleoclimate, lake level fluctuation and faunal composition from the drill cores obtained from Lake Malawi, Africa. However, fish fossils have never been used to examine changes in African Great Lake vertebrate aquatic communities nor as indicators of changing paleolimnological conditions. Here we present results of analyses of a Lake Malawi core dating back ~144ka that describe and quantify the composition and abundance of fish fossils and report on stable carbon isotopic data (δ13C) from fish scale, bone and tooth fossils. We compared the fossil δ13C values to δ13C values from extant fish communities to determine whether carbon isotope ratios can be used as indicators of inshore versus offshore pelagic fish assemblages. Fossil buccal teeth, pharyngeal teeth and mills, vertebra and scales from the fish families Cichlidae and Cyprinidae occur in variable abundance throughout the core. Carbon isotopic ratios from numerous fish fossils throughout the core range between -7.2 and -27.5%, similar to those found in contemporary Lake Malawi benthic and pelagic fish faunas. These results are the first paleo-record of fish fossils from a Lake Malawi sediment core and the first reported δ13C values from Lake Malawi fish fossils. This approach provides a new methodology and framework for interpreting pelagic versus inshore fish faunas, lake level fluctuations and the evolution of the Lake Malawi fish assemblages. © 2010 Elsevier B.V.
- Scholz, C. A., Cohen, A. S., & Johnson, T. C. (2011). Southern hemisphere tropical climate over the past 145ka: Results of the Lake Malawi Scientific Drilling Project, East Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 303(1-4), 1-2.
- Scholz, C. A., Cohen, A. S., Johnson, T. C., King, J., Talbot, M. R., & Brown, E. T. (2011). Scientific drilling in the Great Rift Valley: The 2005 Lake Malawi Scientific Drilling Project - An overview of the past 145,000years of climate variability in Southern Hemisphere East Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 303(1-4), 3-19.More infoAbstract: The recovery of detailed and continuous paleoclimate records from the interior of the African continent has long been of interest for understanding climate dynamics of the tropics, and also for constraining the environmental backdrop to the evolution and spread of early Homo sapiens. In 2005 an international team of scientists collected a series of scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from interior East Africa. The paleoclimate records, which include lithostratigraphic, geochemical, geophysical and paleobiological observations documented in this special issue of Palaeo3, indicate an interval of high-amplitude climate variability between 145,000 and ~60,000years ago, when several severe arid intervals reduced Lake Malawi's volume by more than 95%. These intervals of pronounced tropical African aridity in the early Late Pleistocene around Lake Malawi were much more severe than the Last Glacial Maximum (LGM), a well-documented period of drought in equatorial and Northern Hemisphere tropical east Africa. After 70,000years ago climate shifted to more humid conditions and lake levels rose. During this latter interval however, wind patterns shifted rapidly, and perhaps synchronously with high-latitude shifts and changes in thermohaline circulation. This transition to wetter, more stable conditions coincided with diminished orbital eccentricity, and a reduction in precession-dominated climatic extremes. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa. © 2010 Elsevier B.V.
- Stone, J. R., Westover, K. S., & Cohen, A. S. (2011). Late Pleistocene paleohydrography and diatom paleoecology of the central basin of Lake Malawi, Africa. PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY, 303(1-4), 51-70.
- Stone, J. R., Westover, K. S., & Cohen, A. S. (2011). Late Pleistocene paleohydrography and diatom paleoecology of the central basin of Lake Malawi, Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 303(1-4), 51-70.More infoAbstract: Analysis of sedimentary diatom assemblages (10 to 144. ka) form the basis for a detailed reconstruction of the paleohydrography and diatom paleoecology of Lake Malawi. Lake-level fluctuations on the order of hundreds of meters were inferred from dramatic changes in the fossil and sedimentary archives. Many of the fossil diatom assemblages we observed have no analog in modern Lake Malawi. Cyclotelloid diatom species are a major component of fossil assemblages prior to 35. ka, but are not found in significant abundances in the modern diatom communities in Lake Malawi. Salinity- and alkalinity-tolerant plankton has not been reported in the modern lake system, but frequently dominant fossil diatom assemblages prior to 85. ka. Large stephanodiscoid species that often dominate the plankton today are rarely present in the fossil record prior to 31. ka. Similarly, prior to 31. ka, common central-basin aulacoseiroid species are replaced by species found in the shallow, well-mixed southern basin. Surprisingly, tychoplankton and periphyton were not common throughout prolonged lowstands, but tended to increase in relative abundance during periods of inferred deeper-lake environments. A high-resolution lake level reconstruction was generated by a principle component analysis of fossil diatom and wet-sieved fossil and mineralogical residue records. Prior to 70. ka, fossil assemblages suggest that the central basin was periodically a much shallower, more saline and/or alkaline, well-mixed environment. The most significant reconstructed lowstands are ~. 600. m below the modern lake level and span thousands of years. These conditions contrast starkly with the deep, dilute, dysaerobic environments of the modern central basin. After 70. ka, our reconstruction indicates sustained deeper-water environments were common, marked by a few brief, but significant, lowstands. High amplitude lake-level fluctuations appear related to changes in insolation. Seismic reflection data and additional sediment cores recovered from the northern basin of Lake Malawi provide evidence that supports our reconstruction. © 2010 Elsevier B.V.
- McGlue, M. M., Soreghan, M. J., Michel, E., Todd, J. A., Cohen, A. S., Mischler, J., O'Connell, C. S., Castaneda, O. S., Hartwell, R. J., Lezzar, K. E., & Nkotagu, H. H. (2010). ENVIRONMENTAL CONTROLS ON SHELL-RICH FACIES IN TROPICAL LACUSTRINE RIFTS: A VIEW FROM LAKE TANGANYIKA'S LITTORAL. PALAIOS, 25(7-8), 426-438.
- McGlue, M. M., Soreghan, M. J., Michel, E., Todd, J. A., Cohen, A. S., Mischler, J., O'Connell, C. S., Castañeda, O. S., Hartwell, R. J., Lezzar, K. E., & Nkotagu, H. H. (2010). Environmental controls on shell-rich facies in tropical lacustrine rifts: A view from Lake Tanganyika's littoral. Palaios, 25(7), 426-438.More infoAbstract: Lake Tanganyika, the world's largest tropical rift lake, is unique among its counterparts in East Africa for the remarkable diversity of mollusk-rich sediments in its littoral zone. Molluscan shell beds are, however, a common feature of ancient lacustrine rift deposits and thus a better understanding of their spatial and temporal development is important. Targeted surveys across the littoral region of the Kigoma Basin reveal three surficial shell-rich facies that differ widely in depositional style and geometry. A unifying characteristic of these deposits is the volume of shells of Neothauma tanganyicense, a large, viviparous gastropod endemic to the lake. Reservoir-corrected radiocarbon dating indicates that Neothauma deposits in these surficial sediments are time averaged over at least the last ∼1600 calendar years BP. Preservation of fossil Neothauma shells in the littoral zone depends on both environmental conditions and on post-mortem shell modifications. Interaction between shells and mobile siliciclastic grains, facilitated by wave action and storms, represents a particularly destructive taphonomic process in the study area. Rank scoring of damage to Neothauma suggests that stromatolitic encrustations or early calcite coatings may help mitigate shell destruction caused by hydraulic fragmentation and abrasion. Persistence of Neothauma in littoral beds has important implications for the structuring of specialized communities of shallow-water benthos, as well as for improving analog models for hydrocarbon reservoirs in lacustrine carbonates. © SEPM (Society for Sedimentary Geology).
- Tierney, J. E., Mayes, M. T., Meyer, N., Johnson, C., Swarzenski, P. W., Cohen, A. S., & Russell, J. M. (2010). Late-twentieth-century warming in Lake Tanganyika unprecedented since AD 500. NATURE GEOSCIENCE, 3(6), 422-425.
- Tierney, J. E., Mayes, M. T., Meyer, N., Johnson, C., Swarzenski, P. W., Cohen, A. S., & Russell, J. M. (2010). Late-twentieth-century warming in Lake Tanganyika unprecedented since AD 500. Nature Geoscience, 3(6), 422-425.More infoAbstract: Instrumental observations suggest that Lake Tanganyika, the largest rift lake in East Africa, has become warmer, increasingly stratified and less productive over the past 90 years (refs1,2). These trends have been attributed to anthropogenic climate change. However, it remains unclear whether the decrease in productivity is linked to the temperature rise, and whether the twentieth-century trends are anomalous within the context of longer-term variability. Here, we use the TEX 86 temperature proxy, the weight per cent of biogenic silica and charcoal abundance from Lake Tanganyika sediment cores to reconstruct lake-surface temperature, productivity and regional wildfire frequency, respectively, for the past 1,500 years. We detect a negative correlation between lake-surface temperature and primary productivity, and our estimates of fire frequency, and hence humidity, preclude decreased nutrient input through runoff as a cause for observed periods of low productivity. We suggest that, throughout the past 1,500 years, rising lake-surface temperatures increased the stratification of the lake water column, preventing nutrient recharge from below and limiting primary productivity. Our records indicate that changes in the temperature of Lake Tanganyika in the past few decades exceed previous natural variability. We conclude that these unprecedented temperatures and a corresponding decrease in productivity can be attributed to anthropogenic global warming, with potentially important implications for the Lake Tanganyika fishery. © 2010 Macmillan Publishers Limited. All rights reserved.
- Cohen, A., & Umer, M. (2009). Connecting scientific drilling and human evolution. Eos, 90(14), 122-.
- Cohen, A., Arrowsmith, R., Behrensmeyer, A. K., Campisano, C., Feibel, C., Fisseha, S., Johnson, R., Bedaso, Z. K., Lockwood, C., Mbua, E., Olago, D., Potts, R., Reed, K., Renaut, R., Tiercelin, J., & Umer, M. (2009). Understanding paleoclimate and human evolution through the hominin sites and paleolakes drilling project. Scientific Drilling, 60-65.
- Brown, E. T., Johnson, T. C., Scholz, C. A., Cohen, A. S., & King, J. W. (2008). Reply to comment by Yannick Garcin on "Abrupt change in tropical African climate linked to the bipolar seesaw over the past 55,000 years". Geophysical Research Letters, 35(4).More infoAbstract: In summary, we are not convinced by the arguments of Garcin  that either our interpretation of elevated Zr:Ti or biogenic silica during the Younger Dryas (southward shift of the ITCZ causing more prevalent northerly winds over the north basin of the lake) is in error, or that a similar mechanism was not at work during Greenland stadials in MIS-3. Copyright 2008 by the American Geophysical Union.
- Eggermont, H., Kennedy, D., Hasiotis, S. T., Verschuren, D., & Cohen, A. (2008). Distribution of living larval Chironomidae (Insecta: Diptera) along a depth transect at Kigoma Bay, Lake Tanganyika: implications for palaeoenvironmental reconstruction. African Entomology, 16(2), 162-184.More infoAbstract: We analysed the distribution of living larval Chironomidae (Insecta: Diptera) along a depth transect (0-80 m water depth) at Kigoma Bay in Lake Tanganyika (East Africa) to explore the ecological indicator value of Lake Tanganyika's midge fauna and to delineate the habitat preferences of resident larvae. Additionally, by comparing the taxonomic resolution reached in live versus fossil chironomid studies in this lake, we appraised the general information content of African fossil chironomid assemblages and, therefore, the quality of African chironomid-based palaeoenvironmental reconstructions. We found 141 chironomid specimens, representing two Tanypodinae, one Orthocladinae and 13 Chironominae (seven Chironomini and six Tanytarsini) taxa. All of these are conspecific to larval types encountered in subfossil collections from Lake Tanganyika or smaller East African lakes, but their differential diagnoses are updated here to include exoskeletal elements that are generally better preserved on live specimens. The chironomid assemblage collected in the Kigoma Bay depth samples is dominated by a few species of chironomine detritus and algae feeders, concentrated in areas of high macrophyte density. Additionally, there is a small component of tanypodine predatory taxa, along with several relatively rare, possibly habitat-specialist, taxa of both subfamilies. Our results further indicate that littoral and sublittoral palaeoenvironments in Lake Tanganyika may generally be inferred from high fossil density and diversity. The fairly high correspondence between inferred habitat preference of fossil and live collections in Lake Tanganyika indicates that, in large African lakes, the near-to-offshore gradient in chironomid habitat is imprinted on fossil assemblages. Hence, death assemblages deposited recently at various locations and microhabitats within Lake Tanganyika can be used as modern calibration data for palaeodepth inference. Moreover, Tanganyikan fossil-based taxonomy fully matches the taxonomic resolution reached in this study, so ecological information retrieved from live specimens can immediately be used for palaeoenvironmental studies.
- McGlue, M. M., Lezzar, K. E., Cohen, A. S., Russell, J. M., Tiercelin, J., Felton, A. A., Mbede, E., & Nkotagu, H. H. (2008). Seismic records of late Pleistocene aridity in Lake Tanganyika, tropical East Africa. JOURNAL OF PALEOLIMNOLOGY, 40(2), 635-653.
- McGlue, M. M., Lezzar, K. E., Cohen, A. S., Russell, J. M., Tiercelin, J., Felton, A. A., Mbede, E., & Nkotagu, H. H. (2008). Seismic records of late Pleistocene aridity in Lake Tanganyika, tropical East Africa. Journal of Paleolimnology, 40(2), 635-653.More infoAbstract: New intermediate-resolution, normal-incidence seismic reflection profiles from Lake Tanganyika's central basin capture dramatic evidence of base-level change during two intervals of the late Pleistocene. Four seismically-defined stratigraphic sequences (A-D) tied to radiocarbon-dated sediment cores provide a chronology for fluctuating environmental conditions along the Kalya Platform. Stacked, oblique clinoforms in Sequence C are interpreted as prograding siliciclastic deltas deposited during a major regression that shifted the paleo-lake shore ∼21 km towards the west prior to ∼106 ka. The topset-to-foreset transitions in these deltas suggest lake level was reduced by ∼435 m during the period of deposition. Mounded reflections in the overlying sequence are interpreted as the backstepping remnants of the delta system, deposited during the termination of the lowstand and the onset of transgressive conditions in the basin. The youngest depositional sequence reflects the onset of profundal sedimentation during the lake level highstand. High amplitude reflections and deeply incised channels suggest a short-lived desiccation event that reduced lake level by ∼260 m, interpreted as a product of Last Glacial Maximum (32-14 ka) aridity. Paleobathymetric maps constructed for the two interpreted regressions reveal that despite the positive lake-floor topography created by the Kavala Island Ridge Accommodation Zone, Lake Tanganyika remained a large, mostly connected water body throughout the late Pleistocene. The results of this analysis further imply that Lake Tanganyika is the most drought resistant water body in the East African tropics, and may have acted as a refuge for local and migrating fauna during periods of prolonged aridity. © 2007 Springer Science+Business Media B.V.
- Tierney, J. E., Russell, J. M., Huang, Y., Damste, J., Hopmans, E. C., & Cohen, A. S. (2008). Northern hemisphere controls on tropical southeast African climate during the past 60,000 years. SCIENCE, 322(5899), 252-255.
- Tierney, J. E., Russell, J. M., Huang, Y., S., J., Hopmans, E. C., & Cohen, A. S. (2008). Northern hemisphere controls on tropical southeast African climate during the past 60,000 years. Science, 322(5899), 252-255.More infoPMID: 18787132;Abstract: The processes that control climate in the tropics are poorly understood. We applied compound-specific hydrogen isotopes (δD) and the TEX86 (tetraether index of 86 carbon atoms) temperature proxy to sediment cores from Lake Tanganyika to independently reconstruct precipitation and temperature variations during the past 60,000 years. Tanganyika temperatures follow Northern Hemisphere insolation and indicate that warming in tropical southeast Africa during the last glacial termination began to increase ∼3000 years before atmospheric carbon dioxide concentrations. δD data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial-scale events recorded in Northern Hemisphere monsoonal climate records. This implies that precipitation in tropical southeast Africa is more strongly controlled by changes in Indian Ocean sea surface temperatures and the winter Indian monsoon than by migration of the Intertropical Convergence Zone.
- Brown, E. T., Johnson, T. C., Scholz, C. A., Cohen, A. S., & King, J. W. (2007). Abrupt change in tropical African climate linked to the bipolar seesaw over the past 55,000 years. Geophysical Research Letters, 34(20).More infoAbstract: The tropics play a major role in global climate dynamics, and are vulnerable to future climate change. We present a record of East African climate since 55 ka, preserved in Lake Malawi sediments, that indicates rapid shifts between discrete climate modes related to abrupt warming (D-O) events observed in Greenland. Although the timing of the Malawi events cannot be determined exactly, our age model implies that they occur prior to their Greenland counterparts, consistent with southward excursions of the Intertropical Convergence Zone during Greenland stadials. The magnitude of each of the events recorded in Malawi sediments corresponds to the scale of the subsequent Greenland warming. This suggests that a tropical component of climate sets a template for abrupt high northern latitude climate fluctuations associated with the bipolar seesaw. Copyright 2007 by the American Geophysical Union.
- Cohen, A. S., Stone, J. R., Beuning, K., Park, L. E., Reinthal, P. N., Dettmar, D., Scholz, C. A., Johnsor, T. C., King, J. W., Talbot, M. R., Brown, E. T., & Ivory, S. J. (2007). Ecological consequences of early Late Pleistocene megadroughts in tropical Africa. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 104(42), 16422-16427.
- Cohen, A. S., Stone, J. R., R., K., Park, L. E., Reinthal, P. N., Dettman, D., Scholz, C. A., Johnson, T. C., King, J. W., Talbot, M. R., Brown, E. T., & Ivory, S. J. (2007). Ecological consequences of early Late Pleistocene megadroughts in tropical Africa. Proceedings of the National Academy of Sciences of the United States of America, 104(42), 16422-16427.More infoPMID: 17925446;PMCID: PMC2034256;Abstract: Extremely arid conditions in tropical Africa occurred in several discrete episodes between 135 and 90 ka, as demonstrated by lake core and seismic records from multiple basins [Scholz CA, Johnson TC, Cohen AS, King JW, Peck J, Overpeck JT, Talbot MR, Brown ET, Kalindekafe L, Amoako PYO, et al. (2007) Proc Natl Acad Sci USA 104:16416-16421]. This resulted in extraordinarily low lake levels, even in Africa's deepest lakes. On the basis of well dated paleoecological records from Lake Malawi, which reflect both local and regional conditions, we show that this aridity had severe consequences for terrestrial and aquatic ecosystems. During the most arid phase, there was extremely low pollen production and limited charred-particle deposition, indicating insufficient vegetation to maintain substantial fires, and the Lake Malawi watershed experienced cool, semidesert conditions (
- Felton, A. A., Russell, J. M., Cohen, A. S., Baker, M. E., Chesley, J. I., Lezzar, K. E., McGlue, M. M., Pigati, J. S., Quade, J., Stager, J. C., & Tiercelin, J. J. (2007). Paleolimnological evidence for the onset and termination of glacial aridity from Lake Tanganyika, Tropical East Africa. PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY, 252(3-4), 405-423.
- Scholz, C. A., Johnson, T. C., Cohen, A. S., King, J. W., Peck, J. A., Overpeck, J. T., Talbot, M. R., Brown, E. T., Kalindekafe, L., Amoako, P., Lyons, R. P., Shanahan, T. M., Castaneda, I. S., Heil, C. W., Forman, S. L., McHargue, L. R., Beuning, K. R., Gomez, J., & Pierson, J. (2007). East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 104(42), 16416-16421.
- Scholz, C. A., Johnson, T. C., Cohen, A. S., King, J. W., Peck, J. A., Overpeck, J. T., Talbot, M. R., Brown, E. T., Kalindekafe, L., Y., P., Lyons, R. P., Shanahan, T. M., Castañeda, I. S., Heil, C. W., Forman, S. L., McHargue, L. R., Beuning, K. R., Gomez, J., & Pierson, J. (2007). East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins. Proceedings of the National Academy of Sciences of the United States of America, 104(42), 16416-16421.More infoPMID: 17785420;PMCID: PMC1964544;Abstract: The environmental backdrop to the evolution and spread of early Homo sapiens in East Africa is known mainly from isolated outcrops and distant marine sediment cores. Here we present results from new scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from the continent itself. Our record shows periods of severe aridity between 135 and 75 thousand years (kyr) ago, when the lake's water volume was reduced by at least 95%. Surprisingly, these intervals of pronounced tropical African aridity in the early late-Pleistocene were much more severe than the Last Glacial Maximum (LGM), the period previously recognized as one of the most arid of the Quaternary. From these cores and from records from Lakes Tanganyika (East Africa) and Bosumtwi (West Africa), we document a major rise in water levels and a shift to more humid conditions over much of tropical Africa after ≈70 kyr ago. This transition to wetter, more stable conditions coincides with diminished orbital eccentricity, and a reduction in precession-dominated climatic extremes. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa, but our records provide evidence for dramatically wetter conditions after 70 kyr ago. Such climate change may have stimulated the expansion and migrations of early modern human populations. © 2007 by The National Academy of Sciences of the USA.
- Cohen, A. S., Lezzar, K. E., Cole, J., Dettman, D., Ellis, G. S., Gonneea, M. E., Plisnier, P., Langenberg, V., Blaauw, M., & Zilifi, D. (2006). Late Holocene linkages between decade-century scale climate variability and productivity at Lake Tanganyika, Africa. Handbook of Environmental Chemistry, Volume 5: Water Pollution, 36(2), 189-209.More infoAbstract: Microlaminated sediment cores from the Kalya slope region of Lake Tanganyika provide a near-annually resolved paleoclimate record between ∼2,840 and 1,420 cal. yr B.P. demonstrating strong linkages between climate variability and lacustrine productivity. Laminae couplets comprise dark, terrigenous-dominated half couplets, interpreted as low density underflows deposited from riverine sources during the rainy season, alternating with light, planktonic diatomaceous ooze, with little terrigenous component, interpreted as windy/dry season deposits. Laminated portions of the studied cores consist of conspicuous dark and light colored bundles of laminae couplets. Light and dark bundles alternate at decadal time scales. Within dark bundles, both light and dark half couplets are significantly thinner than within light bundles, implying slower sediment accumulation rates during both seasons over those intervals. Time series analyses of laminae thickness patterns demonstrate significant periodicities at interannual-centennial time scales. Longer time scale periodicities (multidecadal to centennial scale) of light and dark half couplet thicknesses are coherent and in some cases are similar to solar cycle periods on these time scales. Although laminae thickness cycles do not strongly covary with the actual Δ14C record for this same time period, two large Δ14C anomalies are associated with substantial decreases in both light and dark laminae thickness. In contrast to the multidecadal- centennial time scale, significant annual to decadal periodicities, which are broadly consistent with ENSO/PDO forcing and their impact on East African climate, are not coherent between light and dark half couplets. The coherency of light-dark couplets at decadal-centennial time scales, but not at shorter time scales, is consistent with a model of a long-term relationship between precipitation (recorded in wet season dark laminae thickness) and productivity (light laminae thickness), which is not manifest at shorter time scales. We hypothesize that this coupling results from long-term recharging of internal nutrient loading during wet periods (higher erosion of soil P) and reduced loading during drought intervals. The relationship is not expressed on short time scales during which the dominant control on productivity is wind-driven, dry season upwelling, which is uncorrelated with wet-season precipitation. Our record greatly extends the temporal record of this quasi-periodic behavior throughout the late Holocene and provides the first evidence linking decade- to century-scale episodes of enhanced productivity to enhanced precipitation levels and nutrient recharge in a productive tropical lake. © Springer Science+Business Media B.V. 2006.
- Cohen, A. S., Lezzar, K. E., Cole, J., Dettman, D., Ellis, G. S., Gonneea, M. E., Plisnier, P., Langenberg, V., Blaauw, M., & Zilifi, D. (2006). Late Holocene linkages between decade-century scale climate variability and productivity at Lake Tanganyika, Africa. JOURNAL OF PALEOLIMNOLOGY, 36(2), 189-209.
- Bailey, J. V., Cohen, A. S., & Kring, D. A. (2005). Lacustrine fossil preservation in acidic environments: Implications of experimental and field studies for the Cretaceous-Paleogene boundary acid rain trauma. Palaios, 20(4), 376-389.More infoAbstract: The effects of acidification on the preservation of buried lacustrine microfossils were evaluated using experimental tanks to simulate PH, depth, duration of acidification, and buffering conditions below the sediment/water interface of a hypothetical acidified lake. The taphonomic data provided from these experiments suggest that buffering by the host catchment (i.e., the CaCO3 content of the soils and outcrops that underlie the lake and drainage basin) is the primary factor promoting calcareous-fossil preservation under conditions of moderate and severe acidification. Global acid-rain fallout was a likely environmental consequence of the Chicxulub impact event at the Cretaceous-Paleogene boundary, and may have been important at other times in Earth history. Fossil preservation at the K/Pg boundary may have been affected by acidic groundwater leaching. Whereas the duration and intensity of the acid-rain fallout is poorly constrained, acid rain would have had varying effects on the acidity of lacustrine and fluvial environments with different acid-buffering capacities. Variations in acid-buffering capacities of lacustrine and fluvial catchments also may be a factor in the apparent extinction selectivity of non-marine aquatic fauna at the K/Pg boundary. Last appearances of taxa can result from poor preservation conditions or extinction - both of which may result from acidification. Last appearances observed at the species level, but not in higher taxa, may be the result of regional heterogeneities in catchment geology. Understanding local buffering conditions may be important for interpreting the continental fossil record at the K/Pg boundary. Copyright © 2005, SEPM (Society for Sedimentary Geology).
- Balch, D. P., Cohen, A. S., Schnurrenberger, D. W., Haskell, B. J., L., B., Beck, J. W., Cheng, H., & Edwards, R. L. (2005). Ecosystem and paleohydrological response to Quaternary climate change in the Bonneville Basin, Utah. Palaeogeography, Palaeoclimatology, Palaeoecology, 221(1-2), 99-122.More infoAbstract: We report the results of a detailed paleoecological study of the Bonneville basin covering the last ∼280,000 yr. Our study used fossil ostracodes and a sedimentological record obtained from the August 2000 GLAD800 drilling operation at Great Salt Lake. We analyzed 125 samples, taken at ∼1 m intervals from Site 4 (GSL00-4), for ostracodes and other paleoecologic and sedimentologic indicators of environmental change. Multivariate analyses applied to the ostracode data and qualitative analyses of fossil and sedimentological data indicate an alternation between three major environments at the core site over the cored interval: (1) shallow saline or hypersaline lakes; (2) salt or freshwater marshes; and (3) occasional deep freshwater lakes. These environmental changes are consistent with shoreline studies of regional lake level fluctuations, but provide considerable new detail on both the timing and environmental conditions associated with the various lake phases. Our age model (using 14C, U-series, tephra and biostratigraphic chronologies) allowed us to associate the core's record of regional paleohydrology with the marine oxygen isotope stages of global climate change. The core contains continuous records for the last four glacial/interglacial sequences. Salt/freshwater marshes were common during the interglacials and deep freshwater conditions correspond with maximum global ice volume in OIS 2, and before a maximum in global ice during OIS 6. Immediately following deep lake phases, crashes in lake level from rapid desiccation resulted in the deposition of thick evaporite units. Our study suggests that the climate of the Great Salt Lake catchment appears to have been drier during OIS 6 than during OIS 2.We compare our record of environmental change during OIS 6 glaciation with other records from the western United States and find that the overall pattern of climate was similar throughout the West, but differences in the timing of climate change (i.e. when a region became drier or moister) are common. © 2005 Elsevier B.V. All rights reserved.
- Cohen, A. S., Palacios-Fest, M. R., McGill, J., Swarzenski, P. W., Verschuren, D., Sinyinza, R., Songori, T., Kakagozo, B., Syampila, M., O'Reilly, C. M., & Alin, S. R. (2005). Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: I. An introduction to the project. Journal of Paleolimnology, 34(1), 1-18.More infoAbstract: We investigated paleolimnological records from a series of river deltas around the northeastern rim of Lake Tanganyika, East Africa (Tanzania and Burundi) in order to understand the history of anthropogenic activity in the lake's catchment over the last several centuries, and to determine the impact of these activities on the biodiversity of littoral and sublittoral lake communities. Sediment pollution caused by increased rates of soil erosion in deforested watersheds has caused significant changes in aquatic communities along much of the lake's shoreline. We analyzed the effects of sediment discharge on biodiversity around six deltas or delta complexes on the east coast of Lake Tanganyika: the Lubulungu River delta, Kabesi River delta, Nyasanga/Kahama River deltas, and Mwamgongo River delta in Tanzania; and the Nyamuseni River delta and Karonge/Kirasa River deltas in Burundi. Collectively, these deltas and their associated rivers were chosen to represent a spectrum of drainage-basin sizes and disturbance levels. By comparing deltas that are similar in watershed attributes (other than disturbance levels), our goal was to explore a series of historical "experiments" at the watershed scale, with which we could more clearly evaluate hypotheses of land use or other effects on nearshore ecosystems. Here we discuss these deltas, their geologic and physiographic characteristics, and the field procedures used for coring and sampling the deltas, and various indicators of anthropogenic impact. © Springer 2005.
- Cohen, A. S., Palacios-Fest, M. R., Msaky, E. S., Alin, S. R., McKee, B., O'Reilly, C. M., Dettman, D. L., Nkotagu, H., & Lezzar, K. E. (2005). Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: IX. Summary of paleorecords of environmental change and catchment deforestation at Lake Tanganyika and impacts on the Lake Tanganyika ecosystem. Journal of Paleolimnology, 34(1), 125-145.More infoAbstract: Paleorecords from multiple indicators of environmental change provide evidence for the interactions between climate, human alteration of watersheds and lake ecosystem processes at Lake Tanganyika, Africa, a lake renowned for its extraordinary biodiversity, endemism and fisheries. This paper synthesizes geochronology, sedimentology, paleoecology, geochemistry and hydrology studies comparing the history of deltaic deposits from watersheds of various sizes and deforestation disturbance levels along the eastern coast of the lake in Tanzania and Burundi. Intersite differences are related to climate change, differences in the histories of forested vs. deforested watersheds, differences related to regional patterns of deforestation, and differences related to interactions of deforestation and climate effects. Climate change is linked to variations in sediment accumulation rates, charcoal accumulation, lake level and water chemistry, especially during the arid-humid fluctuations of the latter part of the Little Ice Age. Differences between forested and deforested watersheds are manifested by major increases in sediment accumulation rates in the latter (outside the range of climatically driven variability and for the last ∼40 years unprecedented in comparison with other records from the lake in the late Holocene), differences in eroded sediment and watershed stream composition, and compositional or diversity trends in lake faunal communities related to sediment inundation. Variability in regional patterns of deforestation is illustrated by the timing of transitions from numerous sedimentologic, paleoecologic and geochemical indicators. These data suggest that extensive watershed deforestation occurred as early as the late-18th to the early-19th centuries in the northern part of the Lake Tanganyika catchment, in the late-19th to early-20th centuries in the northern parts of modern-day Tanzania, and in the mid-20th century in central Tanzania. Rapid increases in sediment and charcoal accumulation rates, palynological and lake faunal changes occurred in the early-1960s. We interpret this to be the result of greatly enhanced flushing of sediments in previously deforested watersheds triggered by extraordinary rainfall in 1961/62. Regional differences in deforestation histories can be understood in light of the very different cultural and demographic histories of the northern and central parts of the lake shoreline. Incursion of slaving and ivory caravans from the Indian Ocean to the central coast of Lake Tanganyika by the early-19th century, with their attendant diseases, reduced human and elephant populations and therefore maintained forest cover in this region through the late-19th to early-20th centuries. In contrast, the northeastern portion of the lakeshore did not experience the effects of the caravan trades and consequently experienced high human population densities and widespread deforestation much earlier. These studies demonstrate the importance of paleolimnological data for making informed risk assessments of the potential effects of watershed deforestation on long-term lake ecosystem response in the Lake Tanganyika catchment. Differences in sediment yield and lake floor distribution of that yield, linked to factors such as watershed size, slope, and sediment retention, must be accounted for in management plans for both human occupation of currently forested watersheds and the development of future underwater reserves. © Springer 2005.
- Dettman, D. L., Palacios-Fest, M. R., Nkotagu, H. H., & Cohen, A. S. (2005). Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: VII. Carbonate isotope geochemistry as a record of riverine runoff. Journal of Paleolimnology, 34(1), 93-105.More infoAbstract: Evaporation dominates the removal of water from Lake Tanganyika, and therefore the oxygen isotope composition of lake water has become very positive in comparison to the waters entering the lake. The surface water in Lake Tanganyika has remained relatively unchanged over the last 30 years with a seasonal range of +3.2 to +3.5‰ VSMOW. Water from small rivers entering the lake seems to have a δ18O value between -3.5 and -4.0‰, based on scattered measurements. The two largest catchments emptying into the lake deliver water that has a δ18O value between these two extremes. This large contrast is the basis of a model presented here that attempts to reconstruct the history of runoff intensity based on the δ18O of carbonate shells from Lake Tanganyika cores. In order to use biogenic carbonates to monitor changes in the δ18O of mixing-zone water, however, the oxygen isotope fractionation between water and shell carbonate must be well understood. The relatively invariant environmental conditions of the lake allow us to constrain the fractionation of both oxygen and carbon isotope ratios. Although molluskan aragonitic shell δ18O values are in agreement with published mineral-water fractionations, ostracode calcite is ∼1.2‰ more positive than that of inorganic calcite precipitated under similar conditions. Ostracode shell δ18O data from two cores from central Lake Tanganyika suggest that runoff decreased in the first half of this millennium and has increased in the last century. This conclusion is poorly constrained, however, and much more work needs to be done on stable isotope variation in both the waters and carbonates of Lake Tanganyika. We also compared the δ13C of shells against predicted values based solely on the δ13C of lake water dissolved inorganic carbon (DIC). The ostracode Mecynocypria opaca is the only ostracode or mollusk that falls within the predicted range. This suggests that M. opaca has potential for reconstructing the carbon isotope ratio of DIC in Lake Tanganyika, and may be a useful tool in the study of the history of the lake's productivity and carbon cycle. © Springer 2005.
- McIntyre, P. B., Michel, E., France, K., Rivers, A., Hakizimana, P., & Cohen, A. S. (2005). Individual- and assemblage-level effects of anthropogenic sedimentation on snails in Lake Tanganyika. Conservation Biology, 19(1), 171-181.More infoAbstract: Human impacts on aquatic biodiversity are often measured at the assemblage or community level, although it has been suggested that individual-level measures are more sensitive. We evaluated the effects of anthropogenic sedimentation on endemic snails in Lake Tanganyika, East Africa, by comparing assemblage-level (i.e., species richness, evenness, and abundance) and individual-level (i.e., frequencies of predation and parasitism, fecal organic content, life history) data between sediment-disturbed and reference sites. Previous studies have indicated that sedimentation kills snails and reduces mollusc diversity in this system, but we found little evidence of changes in species richness, evenness, or snail abundance at the levels of sedimentation recorded. In contrast, individual-level data revealed a variety of differences associated with sedimentation. Frequencies of shell scarring by predatory crabs and castration by parasitic trematodes were significantly lower at disturbed sites, indicating shifts in interspecific interactions. Snails ingested large amounts of inorganic sediments at disturbed sites, suggesting a reduction in food quality. In addition, sedimentation was associated with a large downward shift in size distribution within some species and reproduction at smaller size. These strong patterns in individual-level data contrast with the lack of effects at the assemblage level. We argue that incorporating individual-level measures will often enhance the sensitivity of impact surveys and may reveal effects of disturbance on important interspecific interactions.
- McKee, B. A., Cohen, A. S., Dettman, D. L., Palacios-Fest, M. R., Alin, S. R., & Ntungumburanye, G. (2005). Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: II. Geochronologies and mass sedimentation rates based on 14C and 210Pb data. Journal of Paleolimnology, 34(1), 19-29.More infoAbstract: We established sediment geochronologies for cores from eight deltaic areas in Lake Tanganyika (the Lubulungu, Kabesi, Halembe, Malagarasi, Nyasanga/Kahama, Mwamgongo, Nyamusenyi, and Karonge/Kirasa River deltas), recording a range of watershed disturbance histories from the eastern margin of this African rift valley lake. Cores from currently disturbed sites on the central Tanzanian coast display remarkably uniform and low rates of sediment accumulation from the 18th century until the early 1960s, when a synchronous and dramatic rise in rates occurs. Through this same time interval sedimentation rates offshore from undisturbed Tanzanian watersheds either remain unchanged or decline. Further north, at disturbed sites along the northern Tanzania and Burundi coasts, the pattern of sedimentation rate increase is more complex. Although a mid-late 20th century increase is also evident in these sites, indications of earlier periods of increasing sediment erosion, dating from the mid-late 19th century, are also evident. Synchronous changes in sediment accumulation rates dating from the early 1960s may be the result of exceptionally wet years triggering an increase in the discharge of previously eroded and unconsolidated alluvium and stream/beach terrace deposits, previously accumulated in the deltas and stream valleys of impacted watersheds. Sedimentation rate impacts of deforestation on lake ecosystems are likely modulated by short-term climatic forcing events, which can impact the specific timing and location of sediment discharge to lakes. © Springer 2005.
- O'Reilly, C., Dettman, D. L., & Cohen, A. S. (2005). Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: VI. Geochemical indicators. Journal of Paleolimnology, 34(1), 85-91.More infoAbstract: Geochemical signals of bulk sedimentary organic matter from three cores from Lake Tanganyika provided information about both internal processes and terrestrial inputs to the lake. Indications of land use change were detected in the geochemical records of the watersheds, and the timing of these changes was consistent with historical records of population demographics. While C:N ratios suggested that the distance from shore might be important in influencing the relative amount of allochthonous vs. autochthonous material, all cores were dominated by autochthonous organic matter. In general, nitrogen isotopes were more positive at disturbed sites, indicating inputs of enriched soil nitrate that was subsequently taken up by phytoplankton. In contrast, carbon isotopes did not reflect land use patterns, and a post-1950s decline in carbon isotope ratios found in all cores may indicate a lake-wide decrease in productivity. These interpretations were consistent with pollen and climate records. © Springer 2005.
- Palacios-Fest, M. R., Alin, S. R., Cohen, A. S., Tanner, B., & Heuser, H. (2005). Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: IV. Lacustrine paleoecology. Journal of Paleolimnology, 34(1), 51-71.More infoAbstract: Fossil invertebrates from cores collected in Lake Tanganyika provide a record of probable nearshore ecological response to recent watershed deforestation and sediment erosion in several East African watersheds. We compared paleoecological profiles (primarily from ostracodes) from watersheds spanning a range of sizes and present-day deforestation disturbance levels to understand the timing and magnitude of faunal changes, and their relationship in time to terrestrially-derived disturbance indicators. Profiles from the Lubulungu and Nyasanga/Kahama Rivers (Tanzania) provide a record of faunal variability in watersheds that are currently undisturbed with respect to deforestation. These records indicate continuous faunal turnover through time. However, this pattern of turnover is accompanied by relatively high levels of diversity throughout the record, with no wholesale extinction events. Ostracode taphonomic data and other fossil abundance data from the Lubulungu area provide strong evidence in support of at least two episodes of lower lake levels, associated with episodes of Late Holocene aridity. Records from deltas of disturbed watersheds at the Kabesi River (Tanzania) and those of Northern Burundi all show a combination of profound and abrupt faunal turnover, in some cases accompanied by local extinction and establishment of a few dominant taxa. At the Mwamgongo River delta, fed from a very small, disturbed watershed, species turnover was subtler. In disturbed watershed cores showing abrupt faunal changes the transitions mostly occurred in the late 19th to early 20th centuries, predating the major mid-20th century increase in sediment mass accumulation rates, with the latter only correlated with changing fossil abundance and flux. However, the earlier faunal community changes are contemporaneous with both palynological and geochemical changes in the core profiles indicative of changing land-use patterns. This suggests that lacustrine ecosystem response to deforestation was a two-stage process, with an earlier phase of response to changing quality of sediments or dissolved matter being discharged from the watershed, and a subsequent phase responding to increased quantity of sediment. © Springer 2005.
- Palacios-Fest, M. R., Cohen, A. S., Lezzar, K., Nahimana, L., & Tanner, B. M. (2005). Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: III. Physical stratigraphy and charcoal analysis. Journal of Paleolimnology, 34(1), 31-49.More infoAbstract: Documenting the history of catchment deforestation using paleolimnological data involves understanding both the timing and magnitude of change in the input of erosional products to the downstream lake. These products include both physically-eroded soil and the byproducts of burning, primarily charcoal, which arise from both intentional and climatically-induced changes in fire frequency. As a part of the Lake Tanganyika Biodiversity Project's special study on sedimentation, we have investigated the sedimentological composition of seven dated cores from six deltas or delta complexes along the east coast of Lake Tanganyika: the Lubulungu River delta, the Kabesi River delta, the Nyasanga/Kahama River delta, and the Mwamgongo River delta in Tanzania, and the Nyamusenyi River delta and Karonge/Kirasa River delta in Burundi. Changes in sediment mass accumulation rates, composition, and charcoal flux in the littoral and sublittoral zones of the lake that can be linked to watershed disturbance factors in the deltas were examined. Total organic carbon accumulation rates, in particular, are strongly linked to higher sediment mass accumulation from terrestrial sources, and show striking mid-20th century increases at disturbed watershed deltas that may indicate a connection between increased watershed erosion and increased nearshore productivity. However, changes in sedimentation patterns are not solely correlated with the 20th century period of increasing human population in the basin. Fire activity, as recorded by charcoal accumulation rates, was also elevated during arid intervals of the 13th-early 19th centuries. Some differences between northern and southern sedimentation histories appear to be correlated with different histories of human population in central Tanzania in contrast with northern Tanzania and Burundi. © Springer 2005.
- Alin, S. R., & Cohen, A. S. (2004). The live, the dead, and the very dead: Taphonomic calibration of the recent record of paleoecological change in Lake Tanganyika, East Africa. Paleobiology, 30(1), 44-81.More infoAbstract: High-resolution (annual to decadal) paleoecological records of community composition can contribute a long-term perspective to conservation biology on baseline ecological variability and the response of communities to environmental change. We present here a detailed comparison of species assemblage characteristics (species richness, abundance, composition, and occurrence frequency) in live, dead, and recent fossil ostracode samples from Lake Tanganyika, East Africa. This study calibrates the fidelity of paleoecological samples (i.e., both death and fossil assemblages) to live diversity patterns for the purpose of reconstructing community dynamics through time. Both life and death assemblages were collected from rocky sites in a mixed substrate habitat (total of ten sampling visits over 22-month period) over spatial scales of less than a meter to about 3-12 meters. Fossil assemblages were derived from sediment cores collected in sandy substrates adjacent to the rocky sites. Species richness in paleoecological assemblages is comparable to that in a year's accumulation of life assemblages sampled approximately monthly. The temporal resolution of the fossil samples in Lake Tanganyika could thus be as short as one year. Species abundance distributions were statistically indistinguishable among data sets. Rank abundance tests demonstrated that death and fossil assemblages were quite similar, although life assemblages differed substantially in the composition of their dominant species. Species composition differences between life and paleoecological assemblages appear to reflect the area of spatial integration represented by an assemblage-i.e., death and fossil assemblages are integrated over multiple habitat types, whereas life assemblages dominantly represent the rocky habitats where they were collected. Species occurrence frequencies in paleoecological data identified ecologically persistent species and may be useful for delimiting local species pools. Analysis of sampling efficiency indicates that approximately 28% of species in each paleoecological assemblage are "unique"; i.e., they are not likely to be present in an additional subsample from the same sample. Ordination reveals that life assemblages of ostracodes are characterized by high spatiotemporal heterogeneity. Variability in species composition was lower in paleoecological assemblages, presumably as a result of spatial and temporal averaging. Death and fossil assemblages of Lake Tanganyika appear to preserve many characteristics of living benthic ostracode assemblages with high fidelity. Spatiotemporal averaging allows paleoecological assemblages to render information about the average composition of ostracode communities over short timescales, at spatial scales of several meters, and across habitat types. Sampling shell assemblages in surficial sediments thus represents a more efficient way of assessing the average ecological conditions at a locality than repeated live sampling. Furthermore, paleoecological analyses can generate novel insights into long-term community variability and membership with direct relevance to conservation. © 2004 The Paleontological Society. All rights reserved.
- Alin, S. R., & Cohen, A. S. (2003). Lake-level history of Lake Tanganyika, East Africa, for the past 2500 years based on ostracode-inferred water-depth reconstruction. Palaeogeography, Palaeoclimatology, Palaeoecology, 199(1-2), 31-49.More infoAbstract: Assemblages of ostracodes from sediment cores illuminate lake-level history at decadal to centennial timescales during the late Holocene at Lake Tanganyika, East Africa. The ostracode-based lake-level curves for several cores resemble both each other and the only previously published lake-level record of comparable resolution for Lake Tanganyika during this interval, successfully reconstructing known highstands, improving the chronology of known lowstands, and contributing new information on late Holocene lake-level variability at this important tropical African location. In agreement with other late Holocene records from East Africa, the surface level at Lake Tanganyika reflects predominantly arid conditions throughout this interval, interrupted by relatively brief episodes of higher precipitation and lake level. The most pronounced lowstand in the record occurs at ∼ 200-0 BC, with other significant lowstands dating to the intervals ∼ 200-500 AD, ∼ 700-850 AD, the Medieval Warm Period (MWP; ∼ 1050-1250 AD at Lake Tanganyika), and the latter part of the Little Ice Age (LIA; ∼ 1550-1850 AD). The most important wet intervals in the lake-level record are centered on ∼ 500 AD, ∼ 1500 AD, and ∼ 1870 AD. The highstands and lowstands reported here for Lake Tanganyika appear to be fairly coherent with other records of rainfall throughout East Africa during the MWP and the LIA. Prior to the MWP, paleoclimate records are apparently less coherent, although this may be a reflection of the resolution and abundance of recent paleoclimatic data available for this climatically complex region. © 2003 Elsevier B.V. All rights reserved.
- O'Reilly, C. M., Alin, S. R., Piisnier, P., Cohen, A. S., & McKee, B. A. (2003). Climate change decreases aquatic ecosystem productivity of Lake Tanganyika, Africa. Nature, 424(6950), 766-768.More infoPMID: 12917682;Abstract: Although the effects of climate warming on the chemical and physical properties of lakes have been documented, biotic and ecosystem-scale responses to climate change have been only estimated or predicted by manipulations and models. Here we present evidence that climate warming is diminishing productivity in Lake Tanganyika, East Africa. This lake has historically supported a highly productive pelagic fishery that currently provides 25-40% of the animal protein supply for the populations of the surrounding countries. In parallel with regional warming patterns since the beginning of the twentieth century, a rise in surface-water temperature has increased the stability of the water column. A regional decrease in wind velocity has contributed to reduced mixing, decreasing deep-water nutrient upwelling and entrainment into surface waters. Carbon isotope records in sediment cores suggest that primary productivity may have decreased by about 20%, implying a roughly 30% decrease in fish yields. Our study provides evidence that the impact of regional effects of global climate change on aquatic ecosystem functions and services can be larger than that of local anthropogenic activity or overfishing.
- Park, L. E., Cohen, A. S., Martens, K., & Bralek, R. (2003). The impact of taphonomic processes on interpreting paleoecologic changes in large lake ecosystems: Ostracodes in Lakes Tanganyika and Malawi. Journal of Paleolimnology, 30(2), 127-138.More infoAbstract: Nonmarine ostracodes are often used as proxy indicators for the biotic response to climate as well as anthropogenic changes in large lakes. Their large numbers, small size and sensitivities to environmental conditions make them ideal for assessing how organisms respond to environmental perturbations. However, little is known about the various taphonomic processes related to preserving these organisms in the lacustrine fossil record. Without understanding the amount of time averaging associated with these assemblages, any interpretation of their biodiversity and paleoecology may be problematic. To address these issues, we conducted actualistic experiments to determine transport, time-averaging, and the amount of taphonomic bias in ostracode sub-fossil assemblages. Sand transport experiments revealed significant mixing at all sites at shallower depths and significant mixing on rocky substrates but not sandy ones. Comparisons with ostracode material collected along the experimental transects support this model and demonstrate time averaging in both the sandy and rocky substrates. Preservational models were derived from the experimental data and applied to interpreting the paleobiologic record of ostracodes from piston cores in both Lake Tanganyika and Malawi. The core record reveals assemblages that have undergone significant time-averaging, and in the case of Lake Malawi, preservational degradation. In the core examined from Tanganyika, most assemblages resemble the time-averaged experimental model with respect to species richness, percentage of articulated shells and heavy bias towards adult dead individuals. In the Malawi cores, most of the valves were preserved only as internal molds. The taphonomic signature of these samples resemble the time-averaged assemblages of Tanganyika cores, even though carapaces are not often present. Both the experimental and live/dead valve data suggest significant time-averaging and transport, smearing seasonal-yearly data in some environments involved in using ostracodes to assess biotic changes as a result of climate and or anthropogenically-induced environmental change. Ostracode species richness estimates were impacted by time averaging because transport of dead valve material occurs at high percentages in the shallow depths and on the rocky substrates, suggesting that the ostracode death assemblages in these areas will not reflect living populations. In addition, ecologic models based only upon death assemblages will be less resolved than those based upon live assemblages. A time averaging index was derived using the % dead juveniles ratio, as well as sedimentation rate and information on the population dynamics, if known.
- Alin, S. R., O'Reilly, C. M., Cohen, A. S., Dettman, D. L., Palacios-Fest, M. R., & McKee, B. A. (2002). Effects of land-use change on aquatic biodiversity: A view from the paleorecord at Lake Tanganyika, East Africa. Geology, 30(12), 1143-1146.More infoAbstract: Population growth and watershed deforestation in northwestern Tanzania threaten the biodiversity of Lake Tanganyika through erosion and habitat degradation. We used cores collected offshore from Gombe Stream National Park and a deforested watershed to reconstruct how land-use changes in the Gombe Stream area since A.D. 1750 have affected lake biodiversity. Paleoenvironmental and paleoecological data reveal substantial changes in mass accumulation rates for sediment and organic matter, nitrogen stable isotope values, and benthic species composition offshore from the deforested watershed since 1880. Comparable changes were not observed offshore from the park.
- Dettman, D. L., Palacios-Fest, M., & Cohen, A. S. (2002). Comment on G. Wansard & F. Mezquita, the response of ostracode shell chemistry to seasonal change in a Mediterranean freshwater spring environment. Journal of Paleolimnology, 27(4), 487-491.More infoAbstract: In a study of the minor element chemistry of ostracode shells, Wansard and Mezquita (2001) concluded that the Mg/Ca and Sr/Ca of the ambient water controlled the respective ratios in ostracode calcite. Contrary to their conclusion that minor element chemistry is not influenced by temperature, we find a very strong statistical correlation (r = 0.97) between temperature and shell chemistry in their data. This discrepancy apparently arises due to their use of a partition coefficient model of shell chemistry that masks a number of strong correlations in their data. We argue here that the partition coefficient model is not appropriate for this biologically mediated carbonate, and that a broader range of possible controls on shell chemistry needs to be tested.
- Lezzar, K. E., Tiercelin, J., Turdu, C. L., Cohen, A. S., Reynolds, D. J., Gall, B. L., & Scholz, C. A. (2002). Control of normal fault interaction on the distribution of major Neogene sedimentary depocenters, Lake Tanganyika, East African rift. AAPG Bulletin, 86(6), 1027-1059.More infoAbstract: The Tanganyika continental rift basin is one of the most important structural features of the East African rift system and provides an opportunity to observe the early stages of rift basin development unobscured by postrift deformation and erosion. The geometry of half grabens and their zones of linkage have a great influence on rift development and depositional environments. Topographic features associated with zones of linkage between half grabens exert a direct control on drainage basin evolution, sediment supply, and synrift stratigraphy. Previous structural studies, based on widely spaced (~15 km) seismic reflection profiles, focused mainly on large-scale geometrical fault descriptions and not on the spatial and temporal linkage of the individual border faults controlling each half graben. In this article, using newly available basin age estimates, multichannel seismic reflection data, high-resolution single-channel sparker seismic data, and onshore structural data (remote directioning and microstructural field observations), we have constructed a detailed late Miocene-Holocene kinematic model for the evolution of the northern part of the Lake Tanganyika rift basin. A classification of fault interaction geometry is proposed to describe the initiation and development through time of major depocenters. Fault correlation lessons are provided for exploration seismic interpreters in extensional settings. The development of the depocenters of northern Lake Tanganyika is complex, and this article clearly shows that antecedent structures control subbasin initiation and development. As the rift evolves, border faults become dominant, producing more continuous and elongate depocenters, although the influence of transverse structures is still evident.
- O'Reilly, C., Hecky, R. E., Cohen, A. S., & Plisnier, P. -. (2002). Interpreting stable isotopes in food webs: Recognizing the role of time averaging at different trophic levels. Limnology and Oceanography, 47(1), 306-309.More infoAbstract: Lake Tanganyika, East Africa, has a simple pelagic food chain, and trophic relationships have been established previously from gut-content analysis. Instead of expected isotopic enrichment from phytoplankton to upper level consumers, there was a depletion of 15N in August 1999. The isotope signatures of the lower trophic levels were an indicator of a recent upwelling event, identified by wind speed and nitrate concentration data, that occurred over a 4-d period several days prior to sampling. The isotope structure of the food web suggests that upwelled nitrate is a nutrient source rapidly consumed by phytoplankton, but the distinctive signature of this nitrate is diluted by time averaging in the upper trophic levels. This time averaging is a consequence of the fact that the isotopic signature of an organism is related to variable nitrogen sources used throughout the life of the organism. This study illustrates the importance of recognizing differences in time averaging among trophic levels.
- Park, L. E., Martens, K., & Cohen, A. S. (2002). Phylogenetic relationships of Gomphocythere (Ostracoda) in Lake Tanganyika, East Africa. Journal of Crustacean Biology, 22(1), 15-27.More infoAbstract: We examined the distribution of 44 morphological characters for 16 extant species of an ostracode genus, Gomphocythere, in Africa, to test hypotheses concerning character development and speciation patterns. Using heuristic searches conducted with the phylogenetic reconstruction program PAUP (beta version, 4.0), we found 2 trees of 98 steps (CI = 0.56). The skewness of tree length distribution reveals significant phylogenetic structure in the data. Nodes are supported by 1 to 11 character-state changes, and these character changes are sometimes reversed or paralleled elsewhere, accounting for much of the homoplasy in the reconstructions. By systematically removing both hard- and soft-part characters in separate analyses, hard-part characters were found to be far more homoplasious in their distribution across the phylogenetic tree, while soft parts are minimally homoplasious, suggesting that they are far more conservative while the hard parts are more prone to ecophenotypic variation. This phylogeny provides the basis for evaluating speciation mechanisms and the role of ecological factors in the diversification of ostracodes in this lake system.
- Cohen, A. S. (2000). Linking spatial and temporal change in the diversity structure of ancient lakes: Examples from the ecology and palaeoecology of the Tanganyikan ostracods. Advances in Ecological Research, 31, 521-537.More infoAbstract: The linked questions of what is a community and how does it change through space and time are some of the most long-lasting and vexing issues in ecology. In part, this reflects the different scales of time and space from which researchers draw their data, yet the issue is of great practical importance because it impinges on decision making in conservation biology. In offering the potential for linking differently scaled studies from both ecology and palaeoecology, ancient lakes are ideal areas in which to investigate this problem. High degrees of endemism and morphological specializations in the faunas of these lakes suggest that ecological interactions among such organisms are also likely to be complex, highly deterministic and stable, as a result of long periods of coevolved interactions. Data from long-term studies of fish ecology in Lake Tanganyika support this notion of highly evolved interactions and community stability, and have served as a general model for understanding ecological interactions in ancient lakes. However, the highly endemic and diverse ostracods of Lake Tanganyika do not conform to this model. Ostracod species associations are extremely variable in space, probably as a result of local colonization and extinction events within local population patches. Whereas individual species show affinities for particular environments, the assemblage observed in a given locality is highly unpredictable. Palaeoecological analyses of sediment cores also show species composition to have varied greatly over periods of hundreds of years. In some cases, however, this assemblage variability is accompanied by stability in total species richness. These results suggest that several models of community assembly may be relevant to ancient lake faunas, and that caution must be exercised in applying any particular model of community structure or stability to conservation biology and biodiversity management. © 2000.
- Cohen, A. S., Palacios-Fest, M. R., Negrini, R. M., Wigand, P. E., & Erbes, D. B. (2000). A paleoclimate record for the past 250,000 years from Summer Lake, Oregon, USA: II. Sedimentology, paleontology and geochemistry. Journal of Paleolimnology, 24(2), 151-182.More infoAbstract: We have obtained a detailed paleoenvironmental record in the Summer Lake Basin, Oregon (northwestern Great Basin, US) spanning from 250 ka - 5 ka. This record is derived from core and outcrop sites extending from a proximal deltaic setting to near the modern depocenter. Lithostratigraphic, paleontologic (ostracodes and pollen) and geochemical indicators all provide evidence for hydroclimate and climate change over the study interval. Lithostratigraphic analysis of the Summer Lake deposits allows subdivision into a series of unconformity - or paraconformity-bound lithosomes. The unconformity and facies histories indicate that the lake underwent several major lake-level excursions through the Middle and Late Pleistocene. High stands occurred between-200 and-165 ka. between -89 and 50 ka and between -25 and 13 ka. Uppermost Pleistocene and Holocene sediments have been removed by deflation of the basin, with the exception of a thin veneer of late Holocene sediment. These high stands correspond closely with Marine Oxygen Isotope Stages 6, 4 and 2. within the margin of error associated with the Summer Lake age model. A major unconformity from -158 ka until -102 ka (duration varies between sites) interrupts the record at both core and outcrop sites. Lake level fluctuations, in turn are closely linked with TOC and salinity fluctuations, such that periods of lake high stands correlate with periods of relatively low productivity, fresher water and increased water inflow/evaporation ratios. Paleotemperature estimates based on palynology and geochemistry (Mg/Ca ratios in ostracodes) indicate an overall decrease in temperature from -236 ka-165 ka, with a brief interlude of warming and drying immediately after this (prior to the major uncomformity). This temperature decrease was superimposed on higher frequency variations in temperature that are not evident in the sediments deposited during the past 100 ka. Indicators disagree about temperatures immediately following the unconformity (-102-95 ka), but most suggest warmer temperatures between -100-89 ka, followed by a rapid and dramatic cooling event. Cooler conditions persisted throughout most of the remainder of the Pleistocene at Summer Lake, with the possible exception of brief warm intervals about 27-23 ka. Paleotemperature estimates for the proximal deltaic site are more erratic than for more distal sites, indicative of short term air temperature excursions that are buffered in deeper water. Estimates of paleotemperature from Mg/Ca ratios are generally in good agreement with evidence from upland palynology. However, there is a significant discordance between the upland pollen record and lake indicators with respect to paleoprecipitation for some parts of the record. Several possibilities may explain this discordance. We favor a direct link between lake level and salinity fluctuations and climate change, but we also recognize the possibility that some of these hydroclimate changes in the Summer Lake record may have resulted from episodic drainage captures of the Chewaucan River between the Summer Lake and Lake Abert basins.
- Cohen, A. S., Scholz, C. A., & Johnson, T. C. (2000). The International Decade of East African Lakes (IDEAL) drilling initiative for the African Great Lakes. Journal of Paleolimnology, 24(2), 231-235.
- Negrini, R. M., Erbes, D. B., Faber, K., Herrera, A. M., Roberts, A. P., Cohen, A. S., Wigand, P. E., & Foit Jr., F. F. (2000). A paleoclimate record for the past 250,000 years from Summer Lake, Oregon, USA: I. Chronology and magnetic proxies for lake level. Journal of Paleolimnology, 24(2), 125-149.More infoAbstract: This study presents the age control and environmental magnetism components of a new, late Pleistocene paleoclimate record for the Great Basin of western North America. Two new cores from the Summer Lake sub-basin of pluvial Lake Chewaucan, Oregon, USA are correlated to basin margin outcrops on the basis of tephrochronology, lithostratigraphy, sediment magnetism and paleomagnetic secular variation. Eleven tephra layers were found in the cores that correlate to tephra identified previously in the outcrop. The Olema ash was also found in one of the cores; its stratigraphic position, relative to 3 dated tephra layers, indicates that its age is 50-55 ka, somewhat younger than has been previously reported. The Summer Lake sediments are divided into deep and shallow lake lithosomes based on sedimentary features. The stratigraphic position of these lithosomes support the tephra-based correlations between the outcrop and the cores. These sediments contain a well resolved record of the Mono Lake Excursion (MLE) and an earlier paleomagnetic excursion as well as a high quality replication of the paleosecular variation immediately above the MLE. Relative sedimentation rates increased dramatically toward the depocenter during intervals of low-lake level. In contrast, during intervals of high-lake level, relative sedimentation rates were comparable along the basin axis from the basin margin to the depocenter. The magnetic mineralogy of the Summer Lake sediments is dominated by pseudo-single domain (titano)magnetite and intervals of high/low magnetite concentration coincide with lithosomes that indicate high/low lake levels. Magnetic grain size also varies in accord with bulk sediment grain size as indicated by the silt/clay ratio. To a first order, variations in magnetic parameters, especially those attributable to the concentration of magnetic minerals, correlate well with global glacial/interglacial oscillations as indicated by marine oxygen isotope stages. This relationship can be explained by increased dissolution of (titano)magnetite minerals as lake level dropped and the lake became more productive biologically. This inference is supported by a correspondence between lower concentrations of magnetite with higher levels of total organic carbon and vice-versa.
- Alin, S. R., Cohen, A. S., Bills, R., Gashagaza, M. M., Michel, E., Tiercelin, J., Martens, K., Coveliers, P., Mboko, S. K., West, K., Soreghan, M., Kimbadi, S., & Ntakimazi, G. (1999). Effects of landscape disturbance on animal communities in Lake Tanganyika, East Africa. Conservation Biology, 13(5), 1017-1033.More infoAbstract: Watershed deforestation, road building, and other anthropogenic activities result in sediment inundation of lacustrine habitats. In Lake Tanganyika, this threatens the survival of many rock-dwelling species by altering the structure and quality of rocky habitats. We investigated the relationship between habitat quality, as related to watershed disturbance intensity, and the biodiversity of faunal communities at three rocky littoral sites of low, moderate, and high disturbance. Turbidity measurements and other environmental observations confirmed that our lake sites represented a gradient of disturbance conditions. We documented differences in species density (number of species per constant area or time), species richness, abundance, and trophic ecology for fishes, molluscs, and ostracods. Fish censuses were performed by scuba divers at 1-20 m and by remotely operated vehicle (ROV) at 40-80 m. In the fish surveys, abundance, species density and richness, and herbivory reached their maxima at intermediate water depths. The depth range of herbivores, however, was restricted at higher-disturbance sites. The ROV fish surveys at the high-disturbance site showed high species richness despite low species density and abundance, and piscivores were proportionally more prevalent than in all other surveys. Molluscs censused by diver quadrats and sieve samples showed decreasing species richness and species density (sieve samples only) with increasing disturbance and no significant abundance trend. Ostracod species richness was similar between low- and moderate-disturbance sites but was markedly lower at the high-disturbance site (species density and abundance data were not available). Our faunal analyses suggest that all three taxonomic groups are negatively affected by sediment inundation but may have varying response thresholds to disturbance. Further, this study emphasized the utility of using complementary survey techniques to monitor and ultimately manage biodiversity in complex freshwater ecosystems.
- Wells, T. M., Cohen, A. S., Park, L. E., Dettman, D. L., & McKee, B. A. (1999). Ostracode stratigraphy and paleoecology from surficial sediments of Lake Tanganyika, Africa. Journal of Paleolimnology, 22(3), 259-276.More infoAbstract: We report here on the first detailed ostracode stratigraphic record to be obtained from late Holocene sediments of Lake Tanganyika. We analyzed four cores, three from the northern lake region and a fourth from a more southern lake locality, that collectively record ostracode assemblages under a variety of disturbance regimes. These cores provide a stratigraphic record of ostracode abundance and diversity, as well as depositional changes over time periods of decades to millennia. We have investigated the fossil ostracodes in these cores by looking at temporal changes of species diversity and population structure for the species present. All four cores provided distinct patterns of ostracode diversity and abundance. BUR-1, a northern lake core obtained close to the Ruisizi River delta, yielded a sparse ostracode record. Karonge 3, another northern core from a site that is closely adjacent to a river delta with high sediment loading, yielded almost no ostracodes. The third core 86-DG-14, taken from a somewhat less disturbed area of the lake, suggests that there have been recent changes in ostracode populations. Through most of the lower portion of this core, ostracode abundance is low and species richness is relatively constant. Above 7 cm there is a marked increase in ostracode abundance and a corresponding decrease in species richness, probably signaling the onset of a major community disturbance, perhaps due to human activities. The southernmost core, 86-DG-32, is from a site that is well removed from influent rivers. Ostracode abundance varies erratically throughout the core, whereas species richness is relatively constant and high throughout the core. The temporal variation evident in ostracode community makeup both within and between the studied cores may be a result of naturally patchy distributions among ostracodes, coupled with local extinctions and recolonizations, or it may reflect inadequate sampling of these high diversity assemblages. In either case, these cores illustrate the potential to obtain high resolution ostracode records from the rich, endemic fauna of Lake Tanganyika that can be used to address questions about the history of community structure and human impacts in this lake.
- Kowalewska, A., & Cohen, A. S. (1998). Reconstruction of paleoenvironments of the Great Salt Lake Basin during the late Cenozoic. Journal of Paleolimnology, 20(4), 381-407.More infoAbstract: This study summarizes the results of micropaleontological, sedimentological, and isotope geochemical analyses of cuttings from five deep wells drilled in the Great Salt Lake (Utah, USA). Spanning the last 5.0 million yrs, our environmental history of the Great Salt Lake distinguishes four intervals based on paleobiological and sedimentological characteristics, using a previously developed tephrochronology for age control. For most of its history, the Great Salt Lake Basin has been occupied by a mixture of marsh, shallow lacustrine and sand flat conditions. In contrast, open lake conditions, typical of the Bonneville cycles and the modern Great Salt Lake apparently have only dominated the basin for the past 0.64-0.8 Ma. The two main structural basins in the study area (the North and South Basins) experienced different lacustrine histories. Large but frequently saline lakes occupied the North Basin after about 0.6 Ma. In the South Basin, ephemeral, saline lacustrine conditions started at 2.1 Ma and developed to full lacustrine conditions at 0.3 Ma. Our paleoenvironmental interpretations are broadly consistent with the aquatic palynological records from the same wells, as well as with the prior core- and outcrop-based lines of evidence. However, the differences in lake history between the North and South Basin have not been previously recognized.
- Cohen, A. S., Lezzar, K. -., A, J. T., & Soreghan, M. (1997). New palaeogeographic and lake-level reconstructions of Lake Tanganyika: Implications for tectonic, climatic and biological evolution in a rift lake. Basin Research, 9(2), 107-132.More infoAbstract: Palaeogeographic and lake-level reconstructions provide powerful tools for evaluating competing scenarios of biotic, climatic and geological evolution within a lake basin. Here we present new reconstructions for the northern Lake Tanganyika subbasins, based on reflection seismic, core and outcrop data. Reflection seismic radiocarbon method (RSRM) age estimates provide a chronological model for these reconstructions, against which yet to be obtained age dates based on core samples can be compared. A complex history of hydrological connections and changes in shoreline configuration in northern Lake Tanganyika has resulted from a combination of volcanic doming, border fault evolution and climatically induced lake-level fluctuations. The stratigraphic expression of lake-level highstands and lowstands in Lake Tanganyika is predictable and cyclic (referred to here as Capart Cycles), but in a pattern that differs profoundly from the classic Van Houten cycles of some Newark Supergroup rift basins. This difference results from the extraordinary topographic relief of the Western Rift lakes, coupled with the rapidity of large-scale lake-level fluctuations. Major unconformity surfaces associated with Lake Tanganyika lowstands may have corresponded with high-latitude glacial maxima throughout much of the mid- to late Pleistocene. Rocky shorelines along the eastern side of the present-day Ubwari Peninsula (Zaire) appear to have had a much more continuous existence as littoral rock habitats than similar areas along the north-western coastline of the lake (adjacent to the Uvira Border Fault System), which in turn are older than the rocky shorelines of the north-east coast of Burundi. This model of palaeogeographic history will be of great help to biologists trying to clarify the evolution of endemic invertebrates and fish in the northern basin of Lake Tanganyika.
- Cohen, A. S., Talbot, M. R., Awramik, S. M., Dettman, D. L., & Abell, P. (1997). Lake level and paleoenvironmental history of Lake Tanganyika, Africa, as inferred from late Holocene and modern stromatolites. Bulletin of the Geological Society of America, 109(4), 444-460.More infoAbstract: Fossil and living stromatolites are abundant around the margins of Lake Tanganyika, Africa, and provide a wealth of paleolimnologic and paleoclimatic information for the late Holocene. Six lines of evidence show that stromatolites and cements are precipitating in the lake today: (1) carbonate saturation state calculations, (2) documentation of living stromatolites and their depth distribution, (3) new stable isotope data showing the lake's present mixing state and ancient evaporation and inflow balance, (4) new radiocarbon data and a reevaluation of apparent 14C ages derived from Lake Tanganyika carbonates, (5) the presence of modern Mg-calcite cements derived from lake waters, and (6) the presence of modern, biologically mediated Mg-calcite precipitates in the lake. Lake Tanganyika's lake levels have been remarkably stable over the past 2800 yr, fluctuating around the marginally open to marginally closed level through most of this time period. Lake lowstands and high δ18O values from the ninth century B.C. to the early fifth century A.D. indicate that the lake basin was comparatively dry during this time. However, the period prior to the most recent opening of Lake Kivu into the Lake Tanganyika basin (ca. A.D. 550) was not marked by major lake lowstands, nor was this opening accompanied by a dramatic lake-level rise. The Kivu opening was roughly coincident with a significant shift toward isotopically lighter (δ18O and δ13C) lake water, which persists today. The lake remained close to its outlet level between the sixth and thirteenth centuries A.D. Lake levels rose between the fourteenth and sixteenth centuries. At some time between the late sixteenth and early nineteenth centuries, lake level fell to perhaps its lowest level in the past 2800 yr. By the early nineteenth century, lake level had begun to rise to the overflow level, apparently the result of a regional increase in precipitation/evaporation ratios. Weak δ18O/δ13C covariance for late Holocene carbonates suggests that the surface elevation of the lake has remained near the outlet level, with only occasional periods of closure. However, there is no simple relationship between solute input from Lake Kivu, isotope input from Lake Kivu, and lake levels in Lake Tanganyika. Lake Kivu waters are the primary source of major ions in Lake Tanganyika, but are much less important in controlling the δ18O and the lake level of Lake Tanganyika. Because the Ruzizi River's discharge into Lake Tanganyika is largely derived from sources other than Lake Kivu, the overflow events in the two lakes have been uncoupled during the late Holocene.
- Ogutu-Ohwayo, R., Hecky, R. E., Cohen, A. S., & Kaufman, L. (1997). Human impacts on the African Great Lakes. Environmental Biology of Fishes, 50(2), 117-131.More infoAbstract: The African Great Lakes are important sources of fishes and water for domestic use, are used as avenues of transport, and receive agricultural, domestic and industrial effluents and atmospheric residues. Some of these lakes have speciose fish faunas of great interest to science. The catchment areas of some of the lakes are highly populated and user conflicts have increased the demands on the lakes' resources. There have been drastic reductions in fish stocks in most of the lakes due to overfishing. Introductions of new fish species, though followed by increases in fish catches, have been accompanied by a decline and in some cases extinction of native fish species. Some of the lakes have been invaded by the water hyacinth, Eichhornia crassipes. Agricultural activities, deforestation and devegetation of the catchment areas have increased siltation, and led to loss of suitable habitats and biodiversity. There are increased nutrient inputs from agriculture, sewage and industrial discharges and combustion processes which can cause eutrophication. There are also increased threats of toxic pollution from industrial waste discharge, mining, pesticides, and oil residues and spills. Climatic changes may also affect thermal stability of the lakes. These factors threaten availability of dietary protein, clean water and biodiversity. National and international efforts are required to manage the fisheries, guide the introduction of exotics, conserve biodiversity, control the water hyacinth, control eutrophication, reduce in-put of contaminants and manage climate change.
- Lezzar, K. E., Tiercelin, J. -., Batist, M. D., Cohen, A. S., Bandora, T., Rensbergen, P. V., Turdu, C. L., Mifundu, W., & Klerkx, J. (1996). New seismic stratigraphy and Late Tertiary history of the North Tanganyika Basin, East African Rift system, deduced from multichannel and high-resolution reflection seismic data and piston core evidence. Basin Research, 8(1), 1-28.More infoAbstract: We present here the initial results of a high-resolution (sparker) reflection seismic survey in Northern Lake Tanganyika, East African Rift system. We have combined these results with data from earlier multichannel reflection seismic and 5-kHz echosounding surveys. The combination of the three complementary seismic investigation methods has allowed us to propose a new scenario for the late Miocene to Recent sedimentary evolution of the North Tanganyika Basin. Seismic sequences and regional tectonic information permit us to deduce the palaeotopography at the end of each stratigraphic sequence. The basin history comprises six phases interpreted to be responses to variations in regional tectonism and/or climate. Using the reflection seismic-radiocarbon method (RSRM), the minimum ages for the start of each phase (above each sequence boundary) are estimated to be: ∼7.4 Ma, ∼1.1 Ma, ∼393-363 ka, ∼295-262 ka, ∼193-169 ka, ∼40-35 ka. Corresponding lowstand lake elevations below present lake level for the last five phases are estimated to have been: ∼650-700 m, ∼350 m, ∼350 m, ∼250 m and ∼160 m, respectively. The latest phase from ∼40-35 ka until the present can be subdivided into three subphases separated by two lowstand periods, dated at ∼23 ka and ∼18 ka. From the late Miocene until the mid Pleistocene, large-scale patterns of sedimentation within the basin were primarily controlled by tectonism. In contrast, from the mid Pleistocene to the present, sedimentation in Lake Tanganyika seems to have responded dramatically to climatic changes as suggested by repeated patterns of lake level fluctuations. During this period, the basin infill history is characterized by the recurrent association of three types of deposits: 'basin fill' accumulations; lens-shaped 'deep lacustrine fans'; and 'sheet drape' deposits. The successive low-lake-level fluctuations decreased in intensity with time as a consequence of rapid sedimentary filling under conditions of declining tectonic subsidence. The climate signal has thus been more pronounced in recent sedimentary phases as tectonic effects have waned.
- Soreghan, M. J., & Cohen, A. S. (1996). Textural and compositional variability across littoral segments of Lake Tanganyika: The effect of asymmetric basin structure on sedimentation in large rift lakes. AAPG Bulletin, 80(3), 382-409.More infoAbstract: Lake Tanganyika, part of the East African rift system, represents one of the most widely cited modern analogs for interpreting ancient rift lakes. To date, few published detailed sedimentologic studies of the modern sediments allow for comparisons to outcrop- and well-bore-scale observations within ancient strata. Four recurrent structural margin types exist along the alternating half-graben structure of the lake: hinged margins, axial margins, accommodation zone margins, and escarpment margins. The hinged margin consists of a series of structurally controlled benches over which long, continuous tracts of bioclastic lag deposits predominate; clastic sands are limited to moderate-size silty deltas and long, narrow shoreface sands. The axial margin is dominated by a wave-dominated, silt-rich delta system. Accommodation zone margins consist of bioclastic lag deposits atop structural highs, whereas carbonate and clastic mud accumulates farther offshore. Escarpment margins contain small fan-delta deposits alternating along shore with talus deposits; offshore carbonate and clastic mud is present away from active gravity-flow deposition. Total organic carbon (TOC) and pyrolysis data from fine-grained samples subtly reflect the contrasts in margin types, but these values are controlled more directly by water depth. Although facies are similar among all margin types, their spatial distribution, in particular the degree to which facies tracts trend parallel to shore, best discriminates among the different margin types. These data suggest that unique but predictable associations of reservoir, seal, and source facies exist along each of the different margin types.
- West, K., & Cohen, A. (1996). Shell microstructure of gastropods from Lake Tanganyika, Africa: Adaptation, convergent evolution, and escalation. Evolution, 50(2), 672-681.More infoAbstract: Gastropod shells from Lake Tanganyika, with their heavy calcification, coarse noded ribbing, spines, apertural lip thickening and repair scars, resemble marine shells more closely than they resemble other lacustrine shells. This convergence between Tanganyikan and marine gastropod shells, however, is not just superficial. Scanning electron microscope (SEM) studies reveal that the Tanganyikan shells are primarily layers of crossed-lamellar crystal architecture (that is, needle-like aragonite crystals arranged into laths that are packed into sheets such that the aragonite needles of adjacent laths are never parallel). The number of crossed-lamellar layers can vary from one to four between different Tanganyikan gastropod species. In species with two or more crossed-lamellar layers, the orientation of the lamellae is offset by approximately 90° between the different layers. The number of crossed-lamellar layers in the shell wall is positively correlated with shell strength and with predation resistance. Three and four crossed-lamellar layers in the shell wall evolved several times independently within the endemic thiarid gastropod radiation in Lake Tanganyika. Repeated origins of three and four crossed-lamellar layers suggest that they may be specific adaptations by Tanganyikan gastropods to strengthen their shells as a defense against shell-crushing predators.
- Cohen, A. S. (1995). Paleoecological approaches to the conservation biology of benthos in ancient lakes: A case study from Lake Tanganyika. Journal of the North American Benthological Society, 14(4), 654-668.
- Tiercelin, J. -., Cohen, A. S., Soreghan, M. J., & Lezzar, K. -. (1994). Pleistocene-modern deposits of the Lake Tanganyika Rift Basin, East Africa: a modern analog for lacustrine source rocks and reservoirs. SEPM Core Workshop, 19, 37-59.More infoAbstract: Bottom sediments of the largest lake of the East African Rift system, Lake Tanganyika (length 650 km; maximum depth 1470 m; volume 18 800 km3) were extensively studied between 1983 and 1986 using a wide range of methods such as reflection seismology, piston coring, and dredging. Interpretation of multifold reflection seismic profiles collected by Project PROBE suggests up to 4 km of sediment has accumulated within local depocenters. In addition, seismic profiles exhibit several seismic discontinuities and associated sequences, interpreted to have resulted from large-scale, temporal changes in local tectonics and/or climate. -from Authors
- Cohen, A. S., Bills, R., Cocquyt, C. Z., & Caljon, A. G. (1993). The impact of sediment pollution on biodiversity in Lake Tanganyika. Conservation Biology, 7(3), 667-677.More infoAbstract: Rapid erosion as a consequence of deforestation is resulting in the discharge of large volumes of sediment into normally clear-water littoral and sublittoral environments. The authors determined species richness patterns among ostracodes, fish, and diatoms for undisturbed, moderately disturbed, and highly disturbed areas. Ostracodes are significantly less diverse in highly disturbed sites than in less disturbed ones for both soft and hard substrate littoral environments, with reductions in species richness ranging from 40-62%. Species richness patterns for profundal ostracodes show smaller differences between low- and high disturbance environments (7-32%) that are not statistically significant. Fish census data show a similar pattern to ostracodes. For water depths where comparative transects were made, species richness was 35-65% lower at high disturbance than at low disturbance sites. Diatoms showed only minor and statistically insignificant reductions in species richness between low and high disturbance sites (15-20%). Ostracodes and fish may be more affected by sedimentation because they are mostly endemic and may require clearwater habitats, whereas the benthic diatom species in the lake are largely cosmopolitan and in many cases also occur in turbid affluent rivers. -from Authors
- Cohen, A. S., Halfpenny, J., Lockley, M., & Michel, E. (1993). Modern vertebrate tracks from Lake Manyara, Tanzania and their paleobiological implications. PALEOBIOLOGY, 19(4), 433-458.
- Cohen, A. S., Soreghan, M. J., & Scholz, C. A. (1993). Estimating the age of formation of lakes: an example from Lake Tanganyika, East African Rift system. Geology, 21(6), 511-514.More infoAbstract: Age estimates for ancient lakes are important for determining their histories and their rates of biotic and tectonic evolution. In the absence of dated core material from the lake's sedimentary basement, several techniques have been used to generate such age estimates. The most common of these, herein called the reflection seismic-radiocarbon method (RSRM), combines estimates of short-term sediment-accumulation rates derived from radiocarbon-dated cores and depth-to-basement estimates derived from reflection-seismic data at or near the same locality to estimate an age to basement. Age estimates from the RSRM suggest that the structural basins of central Lake Tanganyika began to form between 9 and 12 Ma. Estimates for the northern and southern basins are younger (7 to 8 Ma and 2 to 4 Ma, respectively). The RSRM age estimates for Lake Tanganyika are considerably younger than most prior estimates and clarify the extensional history of the western branch of the East African Rift system. -from Authors
- Soreghan, M. J., & Cohen, A. S. (1993). The effects of basin asymmetry on sand composition: Examples from Lake Tanganyika, Africa. Special Paper of the Geological Society of America, 284, 285-301.More infoAbstract: Distinctive compositional trends occur in sand suites collected from structurally diverse segments of Lake Tanganyika (East African Rift System). Climate (subhumid, tropical) and source lithology (mixed granitic and metasedimentary rocks) are generally invariant between the source areas studied. Therefore, differences in sand composition relate directly to differences in compositional modification during transport and deposition of the sands. Sand composition along contrasting segments of the lake basin can be related to the strong structural asymmetry of the basin. We point-counted medium sands from river mouth, deltaic, beach, and shallowwater environments of four structurally distinct, lake-margin settings: (1) escarpment margin (Pemba, Zaire site); (2) hinged margin (Nyanza Lac, Burundi, and Rumonge, Burundi sites); (3) accommodation-zone margin (Magara, Burundi site); and (4) axial margin (Ruzizi River site, Burundi). These four margin-types are typical of the structural morphology in strongly asymmetric half-graben rift basins. Using the Gazzi-Dickinson point counting methodology, margins two through four cluster tightly in QFL space, suggesting similar source lithology. Samples from the Pemba site (escarpment margin) are significantly depleted in feldspar. Because of the uncertainties in interpreting this difference, the escarpment margin sands were not included in subsequent analyses. Variations in sand composition occur between the remaining sites when using the traditional point-counting methodology. The suite of fluvial sands entering the lake basin along the accommodation-zone margin (Magara site) averages 38% rock fragments compared to an average of 15 to 20% and 18% rock fragments for the suite of fluvial sands entering the basin along the hinged or axial margins, respectively. This is a fundamental contrast that correlates directly to differences in drainage basin size. Reworking at the depositional site produces additional compositional differences across the structural margins. In comparing the sample suites for each site, it is the variability in the data that is more important than average composition in highlighting these differences. Minimal compositional modification occurs at the depositional site along both the accommodation-zone margin and the axial margin. In contrast, significant environmental overprinting occurs along the hinged margin sites. Limited compositional modification along the accommodation-zone margin results from the steep depositional gradient and the very narrow high-energy zone which limits reworking of the sediment. The limited reworking and the consequent minimal compositional modification along the axial margin are primarily a function of the high sedimentation rate. The compositional modification (enrichment in quartz) along the hinged margin is a function of low sediment accumulation rates coupled with low subsidence rates, leaving large regions of shallow-water substrate exposed to long periods of reworking. Chemical alteration of labile phases also occurs along the hinged margin through carbonate replacement of feldspar. Our results suggest that, with careful statistical analysis, it is possible to use sandstone composition to distinguish between tectonic margins typical of half-graben basins. Using this approach in ancient studies, it is necessary to collect from several coeval facies among different study sites and to constrain source lithology and climate. In addition, these results are most appropriate for humid-climate basins, where weathering processes are most extreme.
- Tiercelin, J. -., Soreghan, M., Cohen, A. S., Lezzar, K. -., & Bouroullec, J. -. (1992). Sedimentation in large rift lakes: example from the Middle Pleistocene - modern deposits of the Tanganyika Trough, East African Rift System. Bulletin - Centre de Recherche Exploration-Production Elf-Aquitaine, 16(1), 83-111.More infoAbstract: The modern geomorphology of Lake Tanganyika is characterized by two main bathymetric basins, North and South, subdivided in a mosaic of seven strongly asymmetric sub-basins, which are all normally half-grabens. Sedimentation associated with border fault margins includes piedmont deposits, colluvial rockfalls, fan deltas and downslope bars, and locally, at N-S/NW-SE crossing faults, hydrothermal sediments and mineralization. Sedimentation related to axial-deep basins is mainly of autochthonous origin. Wide "sheet drape' sequences are formed by homogeneous or laminated organic-rich muds. -Authors
- Cohen, A., Lockley, M., Halfpenny, J., & Michel, A. E. (1991). Modern vertebrate track taphonomy at Lake Manyara, Tanzania. Palaios, 6(4), 371-389.More infoAbstract: Studies modern tracks at Lake Manyara, to document the environmental and taphonomic controls on track preservation. This closed basin, saline lake closely resembles the depositional setting of many ancient track-bearing strata. It is shown that preburial track survivorship can be modelled as the interaction between three variables: 1) strain susceptibility of a substrate prior to track formation; 2) track loading stress; and 3) secondary reworking rate. -from Authors
- West, K., Cohen, A., & Baron, M. (1991). Morphology and behavior of crabs and gastropods from Lake Tanganyika, Africa: implications for lacustrine predatory-prey coevolution. Evolution, 45(3), 589-607.More infoAbstract: The endemic thiarid and viviparid gastropods from Lake Tanganyika have significantly thicker shells and higher frequencies of terminal apertural lip thickening than closely related cosmopolitan taxa from outside the lake. Tanganyikan gastropods also display considerably higher incidence of shell repair, following nonlethal shell damage, than comspolitan taxa of the same families. The endemic Tanganyikan potamonautid crab Platytelphusa armata (a molluscivore) possesses larger, more robust crushing chelae than other African potamonautid or potamonid crabs. Experiments with the endemic gastropods Spekia, Neothauma, Lavigeria spp., Paramelania spp. and the crab Platytelphusa armata showed that increased size, apertural lip thickness or shell sculpture reduced the successful predation rate of P. armata. Crabs with large chelae have a greater ratio of successful:unsuccessful attacks than crabs with small chelae. Among cases of successful predation, crabs with large chelae used predation methods that required less time and energy than the methods used by crabs with small chelae. Data together provide strong support for the idea that the endemic gastropods and crabs of Lake Tanganyika have coevolved over the past 7 M yr. -from Authors
- Cohen, A. S. (1990). Tectono-stratigraphic model for sedimentation in Lake Tanganyika, Africa. Lacustrine basin exploration - case studies and modern analogs, 137-150.More infoAbstract: Each tectonic setting within rift half-graben basins generates a predictable range of lithofacies architectures. Asymmetry in lithology and strata thickness is the result of lake-level fluctuations interacting with varying rates of sediment accumulation, much of which is structurally influenced. Differences in sequence geometry have implications not only for interpreting ancient rift-lake deposits but also for deposition of economically viable reservoir facies and their juxtaposition with source rocks and caprocks. -from Author
- Cohen, A. S. (1989). Facies relationships and sedimentation in large rift lakes and implications for hydrocarbon exploration: Examples from lakes Turkana and Tanganyika. Palaeogeography, Palaeoclimatology, Palaeoecology, 70(1-3), 65-80.More infoAbstract: Two African lakes, Turkana and Tanganyika, illustrate a spectrum of sediments and facies architectures which can occur in large rift lacustrine basins. They demonstrate contrasts between sediments deposited in a semi-arid, moderately deep, mainly volcanic basin (Turkana) and a semi-humid, extremely deep basin without significant volcanism (Tanganyika). Turkana deposits are dominated by rapidly accumulating, organic-poor, terrigenous muds. Coarse-clastic input is in part limited by ponding in marginal subbasins due to volcanic barriers. Profundal coarse-clastic deposition is rare. Sediments contain little biogenic components except in the sediment-starved south basin. Sediments are also poor in cartonates. Tanganyika deposits are dominated by organic rich, biogenic muds. Steep fault-escarpments and uniform slopes along shelf platform and rift-axis lake margins promote the efficient transport of sands into profundal settings. Total clastic sediment supply into the basin is severely restricted by basin morphology with steep relief, backslopping, a limited drainage basin area and presettling in upstream Lake Kivu. Sediment ponding along margins is rare. Littoral carbonates are common; a consequence of low net clastic sedimentation rates. Many of the differences between facies in the two lakes can be explained by contrasts in basin margin slope and relief, volcanic activity, and climate between the two lakes. The results of this study suggest that lake deposits formed in Tanganyika-type rift basins are more appropriate exploration target for hydrocarbon exploration than those from Turkana-type basins. © 1989.
- Cohen, A. S. (1989). The taphonomy of gastropod shell accumulations in large lakes: an example from Lake Tanganyika, Africa. Paleobiology, 15(1), 26-45.More infoAbstract: An investigation of shell morphometrics of the prosobranch genus Paramelania from Lake Tanganyika shows striking contrasts between some live and dead populations from identical localities. Living populations and surficial dead shells were collected from 15 sublittoral-profundal localities along the east side of the lake. Interpopulation variability in this endemic gastropod is clinal (N-S) for several shell characters. Intrapopulation variability of dead shell populations frequently exceeds that of live populations. Distinctive morphs may be present in a local dead shell population which are absent in the live population from the same locality. However, the phenodeviant dead shell morphology may occur among live snails elsewhere in the lake. Phenodeviant shells may be encrusted, but are unabraded and show no preferred orientation. A model of biogeographic range fluctuations for particular Paramelania morphs during the Holocene, in concert with lake level fluctuations, can account for the shell assemblages seen on the lake floor today. The complex history of these accumulations suggests that taphonomic admixtures may obscure the interpretation of evolutionary sequences in the lacustrine stratigraphic record. -from Author
- Cohen, A. S., & C., T. (1987). Nearshore carbonate deposits in Lake Tanganyika.. Geology,, 15(5), 414-418.More infoAbstract: An exceptionally wide variety of carbonate facies, dominated by high-magnesian calcite, represent the broadest spectrum of carbonate deposits yet reported from any modern lake and serve as important analogues for lacustrine carbonate sequences in the stratigraphic record. -from Authors
- Cohen, A. S., & Johnston, M. R. (1987). Speciation in brooding and poorly dispersing lacustrine organisms. Palaios, 2(5), 426-435.More infoAbstract: Studies of interpopulation variability in brooding and nonbrooding taxa from Lake Tanganyikan ostracodes support the hypothesis that gene flow between populations of lacustrine brooders may be greatly inhibited by extreme localization of gene pools. Significant interpopulation variability occurs among populations of the brooding Mesocythere irsacae in the absence of habitat barriers, whereas sympatric nonbrooding populations of a cytherideid ostracode, n. gen., n. sp. A. show minimal variation over the same range. Extreme genetic isolation may cause rapid speciation and extinction in such populations, owing to the vagaries of small population sizes. When a lake persists for geologically long periods of time selective pressures for excellent dispersal mechanisms may relax. Under such circumstances, clades of lacustrine brooding organisms, which are often poor dispersers, would radiate and suffer extinctions at accelerated rates. -from Authors
- Johnston, M. R., & Cohen, A. S. (1987). Morphological divergence in endemic gastropods from Lake Tanganyika: implications for models of species flock formation. Palaios, 2(5), 413-425.More infoAbstract: Two thiarid gastropods endemic to Lake Tanganyika, which are both stenotopic and rock-dwelling, were investigated because they are believed to be equally subject to environmental barriers to dispersal. A model of allopatric divergence, faciliated by habitat fragmentation, predicts that variation among populations should be large relative to the variation within them, and that organisms equally subject to environmental barriers to dispersal should exhibit similar magnitude and character of morphological divergence. Spekia and members of the Lavigeria species flock appear only in rocky, wave-battered shoals and neither gastropod is known to exhibit wide dispersal. Intervening reaches of sandy and muddy substrates are thought to be barriers to gene flow. Interpopulation morphological variance is greater than intrapopulation variance for both genera, suggesting that divergence is allopatric. However, Spekia shows little morphological variability compared to shallow-water Lavigeria. In graphical analyses of factor scores, Lavigeria forms discrete clusters of morphology related to differences in environment, geographic distribution, and timing of larval broods, all indicative of speciation. The model of allopatric divergence controlled by environmental barriers to dispersal must be reviewed because of 2 incongruent results: sympatry of divergent morphs of Lavigeria, and the observation that members of Lavigeria show much greater endemic divergence than members of Spekia, even though they are thought to be equally poor dispersers. -from Authors
- Cohen, A. S. (1986). Distribution and faunal associations of benthic invertebrates at Lake Turkana, Kenya. Hydrobiologia, 141(3), 179-197.More infoAbstract: The benthic environment and fauna of Lake Turkana were studied during 1978-1979 to determine distribution patterns and associations of benthic invertebrates. Lake Turkana is a large, closed-basin, alkaline lake, located in northern Kenya. Detailed environmental information is currently only available for substrate variations throughout Lake Turkana. Water chemistry and other data are currently inadequate to evaluate their effects on the distribution of Lake Turkana benthic invertebrates. Three weak faunal-substrate associations were discovered at Turkana. A littoral, soft bottom association (large standing crop) is dominated by the corixid Micronecta sp. and the ostracod Hemicypris kliei. A littoral, rocky bottom association, also with a large standing crop, is dominated by various gastropods and insects. A profundal, muddy bottom association, with a very small standing crop, is dominated by the ostracods Hemicypris intermedia and Sclerocypris cf. clavularis and several gastropod and chironomid species. © 1986 Dr W. Junk Publishers.
- Cohen, A. S., & Nielsen, C. (1986). Ostracodes as indicators of paleohydrochemistry in lakes: a Late Quaternary example from Lake Elmenteita, Kenya.. Palaios, 1(6), 601-609.More infoAbstract: The tolerances of many ostracode species to particular hydrochemical parameters are known based upon studies of living taxa from eastern and southern Africa range assemblages. A hydrochemical analysis of ostracodes applied to fossils from a radiocarbon-dated core from Lake Elmenteita, suggests that about 12 000 years BP, Elmenteita was a small, closed lake of Range IV salinity and alkalinity. It underwent a period of decreasing salinity and alkalinity, passing through Range III to a Range II, high-water phase, about 10 000 years BP. The lake remained in Range II prior to its rapid return to a Range IV, highly alkaline and saline, small-lake condition about 8000 years BP. These results demonstrate the great potential for recognizing regional paleohydrologic and paleoclimatic trends from tropical lacustrine ostracodes derived from cores. -from Authors
- Cohen, A. S., Ferguson, D. S., Gram, P. M., Hubler, S. L., & Sims, K. W. (1986). The distribution of coarse-grained sediments in modern Lake Turkana, Kenya: Implications for clastic sedimentation models of rift lakes. Geological Society Special Publication, 25, 127-139.More infoAbstract: The nearshore environment of Lake Turkana, Kenya was studied to determine how coarse clastic sediments are being distributed in the modern lake. Four lake margin study localities were examined in detail: (1) an area of basaltic colluvial headlands; (2) an area of sand, sandy silt and silty mud substrates; (3) an area of highly variable substrate conditions; and (4) an area of alternating basaltic headlands and gravel/shingle terraces. Based upon quantitative observations in these areas and qualitative observations elsewhere in the lake, we believe that two interacting factors have the greatest influence on the distribution of nearshore clastics. The first is a sediment distribution system which is primarily dependent on localized supply, via rockfall and intermittent streams. The second is the presence of physiographic barriers, principally faulted and eroded volcanic flows, which border on local coarse sediment delivery systems and isolate them from adjacent systems. Volcanic barriers may operate at various scales in regulating the delivery systems of clastic sediments in rift lakes, from localized facies disruption, as observed in Lake Turkana, to the isolation of entire sedimentary basins. At the largest levels the presence or absence of volcanic activity may have an important bearing on the controversy of hydrocarbon accumulation in rift lakes. © 1986 The Geological Society.
- Cohen, A. S., Ferguson, D. S., Gram, P. M., Hubler, S. L., & Sims, K. W. (1986). The distribution of coarse-grained sediments in modern Lake Turkana, Kenya: implications for clastic sedimentation models of rift lakes.. Sedimentation in the African Rifts, 127-139.More infoAbstract: Two interacting factors have the greatest influence on the distribution of nearshore clastics. The first is a sediment distribution system which is primarily dependent on localized supply, via rockfall and intermittent streams. The second is the presence of physiographic barriers, principally faulted and eroded volcanic flows, which border on local coarse sediment delivery systems and isolate them from adjacent systems. -from Authors
- Cohen, A. S. (1984). Effect of zoobenthic standing crop on laminae preservation in tropical lake sediment, Lake Turkana, East Africa.. Journal of Paleontology, 58(2), 499-510.More infoAbstract: Fine-grained laminated lake beds are frequently interpreted as having developed under anoxic bottom-water conditions. The absence of pervasive bioturbation is considered to indicate O2 levels too low to support burrowing metazoans. Suggests that food-resource availability may be equally important in laminae preservation.-from Author
- Mount, J. F., & Cohen, A. S. (1984). Petrology and geochemistry of rhizoliths from Plio-Pleistocene fluvial and marginal lacustrine deposits, east Lake Turkana, Kenya ( Koobi Fora Formation).. Journal of Sedimentary Petrology, 54(1), 263-275.More infoAbstract: Recent studies of rhizoliths from the Koobi Fora Formation (Plio-Pleistocene) of east Lake Turkana, Kenya, indicate that their shapes vary with the depositional environment of their host sediment. Vertical rhizoliths are associated with channel-bar and overbank deposits of fluvial origin. Horizontal rhizoliths predominate in facies ascribed to beaches, lagoons, and floodplains associated with ancient Lake Turkana. The rhizoliths consist of sparry and micritic calcite cements whose petrography and geochemistry reflect differences in diagenesis between the two types of root systems.-from Authors
- Cohen, A. S., & Schwartz, H. L. (1983). Speciation in molluscs from Turkana Basin. Nature, 304(5927), 659-660.
- Cohen, A. S., Dussinger, R., & Richardson, J. (1983). Lacustrine paleochemical interpretations based on Eastern and Southern african ostracodes. Palaeogeography, Palaeoclimatology, Palaeoecology, 43(1-2), 129-151.More infoAbstract: Ostracode assemblages in modern African lakes reflect water chemistry variations and so are potentially useful as paleochemical indicators. The water chemistry ranges of 33 modern ostracode taxa have been evaluated for five parameters: total conductivity (K20), Na+, Ca2+, Cl- and alkalinity (CO32- + HCO3-). Strong correlations exist for distribution patterns of ostracodes across all of these parameters except Ca2+. Four, somewhat arbitrary, Ostracode Range Assemblages can be defined, based upon increasing alkalinity and salinity, and named for characteristic taxa. These are: Range I, the Sternocypris assemblage (K20 < 500 μmho) Range II, the Mecynocypria assemblage (K20 = 500-1500 μmho) Range III, the Gomphocythere assemblage (K20 = 1500-4000 μmho) Range IV, the Limnocythere assemblage (K20 > 4000 μmho). An application of the ostracode typology to the fossil record, using a core from Lake Nakuru (Kenya) as an example, suggests a fluctuating alkaline lake prior to about 10,000 yr. B.P., followed by fresh-water conditions until about 8000 yr. B.P. and finally a return to higher alkalinity throughout the remainder of the Holocene. Since the core has also been studied for paleochemical interpretation based upon diatoms, an independent verification of the technique is possible. The two interpretations agree through 80% of the core, suggesting a good reliability for the method. © 1983.
- Cohen, A. S. (1982). Paleoenvironments of root casts from the Koobi Fora Formation, Kenya.. Journal of Sedimentary Petrology, 52(2), 401-414.More infoAbstract: A study of fossil roots and root casts from E Turkana, Kenya, has shown them to be useful paleoenvironmental indicators. Fossil root casts were obtained from the Pleistocene, Upper Member of the Koobi Fora Formation, deposited within the Lake Turkana Basin. Lithofacies and biofacies analysis of the study locality allows the discrimination of several important environments which contain root casts, notably fluvial channels and shallow lacustrine conditions. Studies of plant associations in the Lake Turkana area, and work on modern root morphologies suggest a probable explanation for the associations observed. In arid environments, water availability is a dominant factor in root morphology. A study of root cast morphologies may allow for an assessment of paleogroundwater conditions in nonmarine sediments. -from Author fossil roots paleoenvironmental indicators lithofacies biofacies lacustrine arid environments
- Cohen, A. (1981). Paleolimnological research at Lake Turkana, Kenya.. Palaeoecology of Africa and the surrounding islands. Volume 13, 61-82.More infoAbstract: Major transgressive episodes, initiating prior to 3.2Myr BP, and continuing irregularly until 1.8Myr BP, resulted in important speciation events amongst several groups of lacustrine organisms. A slight increase in alkalinity and salinity is indicated for this time. About 1.8Myr BP, and important climatic shift caused widespread declines in lake levels throughout East Africa. Continual fluctuation in lake level between open and closed basin conditions have characterized the time interval from 1.8Myr BP to the present, with the most recent open lake condition having occurred about 9500 yr BP. -from Author
- Beck, C., Feibel, C. S., Lupien, R., Yost, C. L., Rucina, S., Russell, J. M., Deino, A. L., Sier, M., & Cohen, A. S. (2017, December). Paleoenvironmental change as seen from a multiproxy perspective in the West Turkana Kaitio core (WTK13), Kenya. AGU Annual Meeting. New Orleans, LA: AGU.
- Cassidy, C., Crow, R. S., Cohen, A. S., Beard, S., Thacker, J. O., Felger, T., Pearthree, P., Howard, K. A., & Gootee, B. (2017, October). The subsurface extent of the Bouse Formation in the Lower Colorado River Corridor and possible tectonic implications. GSA Annual Meeting. Seattle, WA: GSA.
- Cohen, A. S., Billingsley, A., Ortiz, K., Anchukaitis, K. J., Deino, A., & Kingston, J. (2017, October). Climate variability across the Plio-Pleistocene transition in East Africa as seen in an HSPDP drill core from Tugen Hills, Kenya, and possible implications for hominin evolution. GSA National Meeting. Seattle, WA: GSA.
- Cohen, A. S., Chapot, M., Roberts, H. M., Asrat, A., Lamb, H., Schaebitz, F., Trauth, M., & Science Team, C. B. (2017, Summer). Dating long lacustrine records from Chew Bahir, Ethiopia using multiple luminescence chronometers. INTIMATE 2017. Aberystwyth, UK: INTIMATE.
- Cohen, A. S., Ferland, T. M., Werne, J. P., Castaneda, I., Lowenstein, T., & Deocampo, D. (2017, December). Oh Magadi! Interpreting isoGDGTs and n-alkanes in a saline tropical lake: Lake Magadi, Kenya.. AGU Ann. Mtg.. New Orleans, LA: AGU.
- Cohen, A. S., Ferland, T., Werne, J., Castaneda, I., Lowenstein, T., Deocampo, D. M., Renaut, R. W., & Owen, R. B. (2017, December). Oh Magadi! Interpreting isoGDGTs and n-alkanes in a saline tropical lake: Lake Magadi, Kenya.. AGU Annual Meeting. New Orleans, LA: AGU.
- Cohen, A. S., Foerster, V., Asrat, A., Ramsey, C., Chapot, M., Dean, J. R., Deocampo, D., & Deino, A. (2017, December). Providing the climatic component in human-climate interaction studies: 550,000 years of climate history in the Chew Bahir basin, a key HSPDP site in southern Ethiopia.. AGU National Meeting. New Orleans, LA: AGU.
- Cohen, A. S., Lowenstein, T., Luo, S., Leet, K., McNulty, E., Owen, R. B., Shen, C. C., Renaut, R., Rabideaux, N., Deocampo, D., Muiruri, V. M., & Deino, A. (2017, October). U-Th disequilibrium dating of Lake Magadi cherts. GSA National Meeting. Seattle, WA: GSA.
- Cohen, A. S., Stockhecke, M., Kingston, J., Beck, C., Brown, E., Deino, A., & Drilling Project Research Team, H. (2017, Spring). Late Pliocene East African climate variability reconstructed from the Baringo Basin (Kenya) HSPDP drill core. PAGES 2017 5th Open Science Meeting. Zaragoza, Spain: PAGES.
- Davies, S. J., Asrat, A., Chapot, M., Cohen, A. S., Dean, J., Deino, A., Foerster, V., Gunter, C., Junginger, A., Just, J., Lamb, H. F., Lane, C., Leng, M., Noren, A., Roberts, H. M., Schaebitz, F., Trauth, M., Viehberg, F., & Team, C. B. (2017, Summer). The Chew Bahir record: half a million years of environmental history from southern Ethiopia. INTIMATE 2017 workshop. Aberystywth, UK: INTIMATE.
- Feibel, C. S., Beck, C. C., Lupien, R., Russell, J., Deino, A., Sier, M., Campisano, C., & Cohen, A. S. (2017, October). Environmental dynamics on an Early Pleistocene lake margin: The WTK13 core at Kaitio, West Turkana, Kenya. GSA National Meeting. Seattle, WA: GSA.
- Ferland, T., Werne, J., Cohen, A. S., Lowenstein, T., Deocampo, D., Renaut, R., & Owen, R. B. (2017, Spring). A climate and environmental context for hominid evolution: Preliminary biomarker and compound specific isotope data from Lake Magadi, Kenya.. Northeastern/North-Central GSA Section Meeting. Pittsburgh, PA: GSA.
- Foerster, V., Asrat, A., Chapot, M., Cohen, A. S., Dean, J. R., Deino, A., Gunter, C., Junginger, A., Lamb, H. F., Leng, M., Roberts, H. M., Schaebitz, F., & Trauth, M. (2017, April). The Chew Bahir Drilling Project (HSPDP). Deciphering climate information from the Chew Bahir sediment cores: Towards a continuous half-million year climate record near the Omo – Turkana key palaeonanthropological Site.. EGU. Vienna, Austria: European Geosciences Union.
- Foerster, V., Asrat, A., Chapot, M., Cohen, A. S., Dean, J., Deino, A., Gunter, C., Junginger, A., Lamb, H. F., Leng, M. L., Roberts, H. M., Schaebitz, F., & Trauth, M. (2017, April). Hominin Sites and Paleolakes Drilling Project: A 500,000-year climate record from Chew Bahir, a key site in southern Ethiopia. EGU. Vienna, Austria: European Geosciences Union.
- HSPDP, T. M., & Cohen, A. S. (2017, October). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Progress towards understanding the paleoenvironmental context of human evolution in eastern Africa.. GSA National Meeting. Seattle, WA: GSA.
- Ivory, S., Barker, P., Cohen, A. S., Kimirei, I., Lane, C., Leng, M., McGlue, M., Msaky, E., Noren, A., Park-Bousch, L. E., Russell, J., Salzburger, W., & Scholz, C. (2017, October). Lake Tanganyika drilling: Addressing world-class scientific questions in paleoclimatology, tectonics and evolutionary biology in Africa’s oldest lake.. GSA National Meeting. Seattle, WA: GSA.
- Lane, C., Asrat, A., Cohen, A. S., Cullen, V., Johnson, T., Lamb, H., Martin-Jones, C., Poppe, S., Schaebitz, F., & Scholz, C. (2017, April). Explosive eruption records from Eastern Africa: filling in the gaps with tephra records from stratified lake sequences,. EGU. Vienna, Austria: European Geosciences Union.
- Leng, M., Dean, J., Asrat, A., Cohen, A. S., Chapot, M., Deino, A., Foerster, V., Lamb, H. F., Roberts, H. M., Schaebitz, F., Trauth, M., & Viehburg, F. (2017, April). A palaeoclimate investigation of the lacustrine sediments from Chew Bahir in Ethiopia spanning multiple glacial-interglacial cycles.. EGU. Vienna, Austria: European Geosciences Union.
- Lupien, R., Russell, J., Campisano, C., Feibel, C., Deino, A., Kingston, J., Potts, R., & Cohen, A. S. (2017, December). A synthesis of Plio-Pleistocene leaf wax biomarker records of hydrological variation in East Africa and their relationship with hominin evolution.. AGU Annual Meeting. New Orleans, LA: AGU.
- Sier, M., Langereis, C., Dupont-Nivet, G., Feibel, C., Joordens, J., van der Lubbe, J., Beck, C., Olago, D. O., Cohen, A. S., & Team Members, H. (2017, April). The top of the Olduvai subchron in a high-resolution magnetostratigraphy from the West Turkana core WTK13, Hominin Sites and Paleolakes Drilling Project (HSPDP).. EGU. Vienna, Austria: European Geosciences Union.
- Stockhecke, M., Brown, E., Beverly, E., Cohen, A. S., Deocampo, D., Potts, R., Behrensmeyer, A. K., Dommain, R., & Drilling Project Research Teams, O. a. (2017, March). Characterization of paleosol maturity using XRF scanning data. XRF Core Scanning. National Taiwan University, Taiwan: National Taiwan University, Taiwan.
- Stockhecke, M., Kingston, J., Beck, C., Brown, E., Cohen, A. S., Deino, A., & Drilling Project Research Time, H. (2017, Spring). Late Pliocene East African climate variability reconstructed from the Baringo Basin (Kenya) HSPDP drill core. PAGES 3rd Young Scientists Meeting. Morillo de Tou, Spain: PAGES.
- Upadhyay, D., Caraveo, C. A., Gomis, E., Hailemichael, M., Bedaso, Z., Aronson, J. L., Cohen, A. S., & Tripati, A. (2017, October). Testing hypotheses for the role of climate change in hominin evolution using the geochemistry of carbonates from the East African rift system. GSA National Meeting. Seattle, WA: GSA.
- Yost, C., Jackson, L., Stone, J., & Cohen, A. S. (2017, October). Sub-decadal phytolith and charcoal records from Lake Malawi, East Africa, indicate that the Toba supereruption at 75ka was not severe enough to cause a human genetic bottleneck. GSA National Meeting. Seattle, WA: GSA.
- Beck, C., Feibel, C., Gravina, A., Van Der Lubbe, J., Joordens, J., Cohen, A. S., Muiruri, V., Leet, K., Rabideaux, N., Billingsley, A., & Mbuthia, A. (2016, Fall). What do you do with “homogeneous” fine-grained intervals? Lessons learned from comparing facies and ostracod records between core and outcrop, West Turkana, Kenya. Geological Society of America Annual Meeting. Denver, CO: GSA.
- Bright, J., Cohen, A. S., & Pearthree, P. (2016, April). Stable isotope (d18O, d13C) data from paired inorganic calcite and biologic calcite analyses suggest a lacustrine origin for the southern Bouse Formation, southwestern AZ and southeastern CA. CA Desert Symposium. Zzyzx, CA: CA Desert Symposium.
- Cohen, A. S. (2015, March 19). Reflections On African Rift Lakes: A Journey Through The History Of The World’s Most Interesting Lakes. Geological Society of Saskatchewan-Invited Speaker. Regina, Saskatchewan: Geological Society of Saskatchewan.
- Cohen, A. S. (2016, July). A 1.2 million year record of ecosystem evolution from Lake Malawi, Africa's most biodiverse lake. Seminar for Geography Education Colloquium, University of Cologne. Cologne, Germany: University of Cologne.
- Cohen, A. S. (2016, June). HSPDP Update. Chew Bahir Drilling Symposium. Aberystwyth, Wales: University of Aberystwyth.
- Cohen, A. S. (2016, June). Scientific Drilling for Human Origins in Africa. University of Aberystwyth Evening Lecture Series. Aberystwyth, Wales, UK: University of Aberystwyth.
- Cohen, A. S. (2016, March). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the environmental and climatic context of human origins through continental drilling. Institute Colloquium Speaker, EAWAG (Swiss Federal Water Research Agency). Kastanienbaum, Switzerland: EAWAG.
- Cohen, A. S. (2016, November). Comparative Mid-Late Pleistocene Environmental Records From Africa, Eastern Europe and Western Asia Covering The Last 400ka And Their Implications For Human Dispersal. Workshop on Human Dispersals in the Late Pleistocene Interdisciplinary Approaches Towards Understanding the Worldwide Expansion of Homo sapiens. Jena, Germany: Max Plack Inst. for the Study of Human History.
- Cohen, A. S. (2016, Spring). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the environmental and climatic context of human origins through continental drilling. Department of Earth Sciences Colloquium, ETH. Zurich, Switzerland: ETH.
- Cohen, A. S. (2016, Spring). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the environmental and climatic context of human origins through continental drilling. University of Bern, Geology Department Colloquium Series. Bern, Switzerland: University of Bern.
- Cohen, A. S. (2016, Spring). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the environmental and climatic context of human origins through continental drilling. Zoology Institute Colloquium, University of Basel. Basel, Switzerland: Zoology Institute, U. Basel.
- Cohen, A. S. (2016, Summer). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the environmental and climatic context of human origins through scientific drilling. Institute of Geosystems and Bioindication Colloquium, University of Braunschweig. Braunschweig, Germany: Institute of Geosystems and Bioindication, University of Braunschweig.
- Cohen, A. S., Blome, M., Ivory, S., King, J., McGlue, M., & Cole, J. E. (2016, April). A ~1.3Ma paleoecological record from scientific drilling at Lake Malawi, East Africa. European Geosciences Union. Vienna, Austria: EGU.
- Davies, S., Robson, P., Lamb, H., Asrat, A., Barker, P., Cohen, A. S., Schaebitz, F., & Trauth, M. (2016, Summer). Preliminary diatom results from Chew Bahir, Ethiopia – a contribution to the Hominin Sites and Paleolakes Drilling Project.. International Diatom Symposium. Quebec City, Quebec CA: International Diatom Symposium.
- Feibel, C., Beck, C., Van der Lubbe, J., Joordens, J., Sier, M., Beverly, E., Campisano, C., & Cohen, A. S. (2016, Fall). The Lorenyang Lake at Kaitio: Outcrop and core perspectives on an Early Pleistocene lake margin. Geological Society of America Annual Meeting. Denver, CO: GSA.
- Ferland, T., Werne, J., Cohen, A. S., Lowenstein, T., Deocampo, D., Renaut, R., Owen, R. B., De Cort, G., & Verschuren, D. (2016, July). Preliminary results of a molecular isotope study of sediments from Lake Magadi, Kenya over the past ~million years. Gordon Organic Geochemistry Research Seminar. Holderness, NH: Gordon Research Conferences.
- Foerster, V., Asrat, A., Cohen, A. S., Gromig, R., Gunter, C., Junginger, A., Lamb, H., Schabitz, F., & Trauth, M. (2016, Spring). The long HSPDP-Chew Bahir record from southern Ethiopia:Scientific Drilling in search of the environmental context of human evolution. German ICDP. Heidelberg, Germany: German International Continental Drilling Program.
- Joordens, J., Beck, C., Sier, M., Van der Lubbe, J., Dupont-Nivet, G., Langereis, C., Vonhof, H., Cohen, A. S., Olago, D., Campisano, C., & Feibel, C. (2016, April). Climate-driven lacustrine dynamics from the Early Pleistocene Lorenyang Lake, Turkana Basin, Kenya. European Geosciences Union. Vienna, Austria: EGU.
- Leng, M., Dean, J., Asrat, A., Cohen, A. S., Foerster, V., Just, J., Klassen, N., Lamb, H., Schabitz, F., Trauth, M., Viehberg, F., & Wagner, B. (2016, April). The ICDP-Hominin Sites and Paleolakes Drilling Project (HSPDP): new data from the Chew Bahir site in Ethiopia. European Geosciences Union. Vienna, Austria: EGU.
- Lupien, R., Russell, J., Cohen, A. S., Feibel, C., Beck, C., & Castaneda, I. (2016, December). Leaf wax biomarker reconstruction of Early Pleistocene hydrological variation during hominin evolution in West Turkana, Kenya.. American Geophysical Union Annual Meeting. San Francisco, CA: AGU.
- McNulty, E., Lowenstein, T., Owen, R. B., Deocampo, D., Muiruri, V., Cohen, A. S., Leet, K., Rabideaux, N., Billingsley, A., & Mbuthia, A. (2016, Fall). The sedimentary record of the Lake Magadi Basin: Core analysis from HSPDP-MAG14 Cores 1A, 1C and 2A.. Geological Society of America Annual Meeting. Denver, CO: GSA.
- Owen, R. B., Muiruri, V., Lowenstein, T., Renaut, R., Cohen, A. S., Deocampo, D., McNulty, E., Leet, K., Rabideaux, N., Billingsley, A., & Mbuthia, A. (2016, Fall). Quaternary environments of the Magadi Basin: Geochemical and microfossil stratigraphic variability. Geological Society of America Annual Meeting. Denver, CO: GSA.
- Schabitz, F., Wagner, B., Viehberg, F., Wennrich, V., Rathmeyer, J., Just, J., Klasen, N., Asrat, A., Lamb, H., Foerster, V., Trauth, M., Junginger, A., Cohen, A. S., & Science Team, H. (2015, Jan. 30-Feb 7). First results from the deep drilling at Chew Bahir (S-Ethiopia). African Quaternary Conference and Workshop. Captetown, South Africa: African Quaternary Association.
- Schaebitz, F., Asrat, A., Lamb, H., Trauth, M., Junginger, A., Foerster, V., Gunter, C., Viehberg, F., Just, J., Roberts, H., Chapot, M., Leng, M., Dean, J., & Cohen, A. S. (2016, December). Chew Bahir, southern Ethiopia: an archive of environmental history during the evolution and dispersal of anatomically modern humans. American Geophysical Union Annual Meeting. San Francisco, CA: AGU.
- Stockhecke, M., Beck, C., Brown, E., Cohen, A. S., Feibel, C., Rabideaux, N., & Sier, M. (2016, April). An Early Pleistocene high-resolution paleoclimate reconstruction from the West Turkana (Kenya) HSPDP drill site.. European Geosciences Union. Vienna, Austria: EGU.
- Tim, L., Owen, R. B., Renaut, R., Deocampo, D., Cohen, A. S., McNulty, E. P., Leet, K., Muiruri, V., Rabideaux, N., Billingsley, A., & Mbuthia, A. (2016, September). Lake Magadi, Kenya: Modern-Pleistocene analog for alkaline saline deposits.. Geological Society of America Annual Meeting. Denver, CO: GSA.
- Werne, J., Ferland, T., Cohen, A. S., Lowenstein, T., Deocampo, D., Renaut, R., & Owen, R. B. (2016, December). A climate and environmental context for hominid evolution: Preliminary biomarker and compound specific isotope data from Lake Magadi, Kenya. American Geophysical Union. San Francisco, CA: AGU.
- Campisano, C., Cohen, A. S., Asrat, A., Feibel, C., Kingston, J., Lamb, H. F., Olago, D., Owen, R. B., Renaut, R., Schabitz, F., Arrowsmith, R., & Ivory, S. (2015, April 14-15). Drilling campaign summary and preliminary results of the Hominin Sites and Paleolakes Drilling Project (HSPDP).. Paleoanthropology Society Annual Meeting. San Francisco, CA: Paleoanthropology Association.
- Cohen, A. S. (2015, August 5). Lakes and watersheds in "deep time": What can we learn about ecological and evolutionary history using lacustrine drill core records. 13th International Paleolimnology Symposium. Lanzhou, China: International Paleolimnology Association.
- Cohen, A. S. (2015, December). Paleobiology/Evolutionary Biology Objectives For Scientific Drilling At Lake Tanganyika And Linkages With Source/Sink Project Components. STEPPE Lake Tanganyika Source To Sink Drilling Workshop. San Francisco, CA: STEPPE Consortium (Sedimentary Geology, Time, Environment, Paleoclimatology, Paleontology, Energy).
- Cohen, A. S. (2015, Feb. 3). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Collecting paleolake drill cores from the East African Rift Valley to document the environmental context of human origins. University of Strasbourg (France) Department Seminar. Strasbourg, France: Geology Department.
- Cohen, A. S. (2015, March 19). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Collecting paleolake drill cores from the East African Rift Valley to document the environmental context of human origins. Geology Department, University of Regina Seminar Series. Regina, Saskatchewan: University of Regina.
- Cohen, A. S. (2015, November). Drill Core Paleoclimate Records from East Africa. The biogeography of modern human origins, diversity, and dispersals from East Africa Workshop. Radcliffe Institute, Harvard University, Cambridge, MA: Radcliffe Institute, Harvard University.
- Cohen, A. S., & Project Team, H. (2015, June 30). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the environment and climate conditions surrounding human evolution through continental drilling. National Museums of Kenya Evening Lecture Series. Nairobi, Kenya: National Museums of Kenya.
- Cohen, A. S., Campisano, C., Arrowsmith, R., Asrat, A., Deino, A., Feibel, C., Hill, A., Kingston, J., Lamb, H., Lowenstein, T., Olago, D., Owen, R. B., Renaut, R., Schabitz, F., Tiercelin, J., & Wynn, J. (2015, Jan 30-Feb 7). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Collecting paleolake drill cores from the East African Rift Valley to document the environmental context of human origins,. African Quaternary Conference and Workshop. Capetown, South Africa: African Quaternary Association.
- Cohen, A. S., Campisano, C., Arrowsmith, R., Asrat, A., Deino, A., Feibel, C., Kingston, J., Lamb, H., Lowenstein, T., Olago, D., Owen, R. B., Renaut, R., Schabitz, F., Trauth, M., & Team Members, H. (2015, November). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the environmental and climatic context of human origins through continental drilling. Lamont Doherty Earth Observatory Geoscience Seminar. LDEO, Columbia University, Piermont, NY: LDEO Geosciences.
- Cohen, A. S., Campisano, C., Arrowsmith, R., Deino, A., Feibel, C., Kingston, J., Lamb, H., Lowenstein, T., Olago, D., Owen, R. B., Renaut, R., Schabitz, F., Trauth, M., & Science Team, H. (2015, October). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the environmental and climatic context of human origins through continental drilling. Center for Integrative Geosciences Seminar Series, University of Connecticut. U. Connecticut, Storrs, CT: Center for Integrative Geosciences, University of Connecticut.
- Cohen, A. S., Campisano, C., Asrat, A., Arrowsmith, R., Deino, A., Feibel, C., Hill, A., Kingston, J., Lamb, H., Lowenstein, T., Olago, D., Owen, B., Renaut, R., Schabitz, F., Trauth, M., & Project Team, H. (2015, September). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the paleoenvironmental and paleoclimatic context of human origins through continental drilling. University of Minnesota-Duluth Geology Department Seminar Series. Duluth, MN: University of Minnesota-Duluth.
- Cohen, A. S., Campisano, C., Asrat, A., Arrowsmith, R., Deino, A., Feibel, C., Hill, A., Kingston, J., Lamb, H., Lowenstein, T., Olago, D., Owen, R. B., Renaut, R., Schabitz, F., Trauth, M., & Members, H. T. (2015, 12-17 April). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the paleoenvironmental and paleoclimatic context of human origins through continental drilling. European Geoscience Union Annual Meeting. Vienna, Austria: EGU.
- Cohen, A. S., Campisano, C., Asrat, A., Arrowsmith, R., Deino, A., Feibel, C., Hill, A., Kingston, J., Lamb, H., Lowenstein, T., Owen, R. B., Renaut, R., Schabitz, F., & Trauth, M. (2015, June). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the paleoenvironmental and paleoclimatic context of human origins through continental drilling. Continental Scientific Drilling Coordination Office Workshop Invited Talk. Minneapolis, MN: CSDCO.
- Cohen, A. S., Campisano, C., Asrat, A., Arrowsmith, R., Deino, A., Feibel, C., Kingston, J., Lamb, H., Lowenstein, T., Olago, D., Owen, R. B., Renaut, R., Schabitz, F., Trauth, M., & Team Members, H. (2015, October). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Understanding the environmental and climatic context of human origins through continental drilling. Occidental College Geology Department Seminar. Los Angeles, CA: Geology Department, Occidental College.
- Feibel, C., Beck, C., Stockhecke, M., Gravina, A., Ortiz, K., Campisano, C., & Cohen, A. S. (2015, October). Seeing Deeper Into The Mud: Insights From The WTK13 Core, West Turkana, Kenya. Geological Society of America Annual Meeting. Baltimore, MD: GSA.
- Foerster, V., Asrat, A., Cohen, A. S., Junginger, A., Schabitz, F., Trauth, M., Lamb, H., & Science Team, H. (2015, March). Three promising tons of sedimentary deposits from Chew Bahir [south Ethiopia] to reconstruct 0.5 Ma of climatic history. ICDP-Germany Colloquium. Bonn, Germany: German International Continental Drilling Program.
- Johnson, T., Werne, J., Brown, E. T., Abbott, A., Berke, M., Halbur, J., Contreras-Quintana, S., Grossheusch, S., Schouten, S., Sinninghe-Damste, J., Lyons, R., Scholz, C., Cohen, A. S., & King, J. (2015, Jan 30-Feb 7). A progressively wetter climate in Southern East Africa over the past million years. African Quaternary Association. Capetown, South Africa: African Quaternary Association.
- Kingston, J., Deino, A., Hill, A., Campisano, C., Garello, D., Sier, M., Yost, C., Stone, J., Cohen, A. S., & Billingsley, A. (2015, October). A Plio-Pleistocene Drill Core From The Baringo Basin, Central Kenyan Rift Valley. Geological Society of America Annual Meeting. Baltimore, MD: GSA.
- Lupien, R., Russell, J., Castaneda, I., Cohen, A. S., & Feibel, C. (2015, October). Leaf Wax Biomarkers As Proxies For Regional Climate Variation During Hominin Evolution. Geological Society of America Annual Meeting. Baltimore, MD: GSA.
- Rabideaux, N., Deocampo, D., Lowenstein, T., Renaut, R., Owen, R. B., Muiruri, V., & Cohen, A. S. (2015, October). Authigenic Minerals As Paleosalinity Indicator From Lake Magadi, Kenya: Based On Xrd Analysis Of HSPDP-Mag Core Material. Geological Society of America Annual Meeting. Baltimore, MD: GSA.
- Renaut, R., Schabitz, F., Project Team, H., Cohen, A. S., Campisano, C., Asrat, A., Arrowsmith, R., Deino, A., Feibel, C., Foerster, V., Hill, A., Ivory, S., Kingston, J., Lamb, H., Lowenstein, T., Olago, D., & Owen, R. B. (2015, July 27- August 2). Initial results of the Hominin Sites and Paleolakes Drilling Project (HSPDP): Collection and interpretation of high resolution lacustrine drill cores from key Plio-Pleistocene paleoanthropological sites in East Africa. International Quaternary Association. Nagoya, Japan: INQUA.
- Schabitz, F., Viehberg, F., Wienrich, V., Rathmeyer, J., Just, J., Klassen, N., Asrat, A., Lamb, H., Foerster, V., Trauth, M., Junginger, A., & Cohen, A. S. (2015, March). Preliminary results from the deep drilling at Chew Bahir, south Ethiopia. ICDP-Germany Colloquium. Bonn, Gemany: German International Continental Drilling Program.
- Yost, C., Cohen, A. S., & Feibel, C. (2015, October). Using Phytoliths To Reconstruct Late Pleistocene Vegetation History From The Hominin Sites And Paleolakes Drilling Project (HSPDP) West Turkana, Kenya, Drill Core. Geological Society of America Annual Meeting. Baltimore, MD: GSA.
- Beck, C., Feibel, C., Henderik, R. L., Gravina, A., Sier, M., Cohen, A. S., & Campisano, C. (2014, October). A fluctuating Pleistocene lake margin: updates from the HSPDP West Turkana Kaitio drill leg. GSA Annual Meeting. Vancouver.
- Bright, J., Cohen, A. S., Dettman, D., & Dorsey, R. (2014, October). Ostracode-based faunal and stable isotope data suggest a mixed marginal marine to stratified lacustrine waterbody interpretation for the southern Bouse Formation, AZ. GSA Annual Meeting. Vancouver.
- Campisano, C., Cohen, A. S., Asrat, A., Feibel, C., Kingston, J., Lamb, H., Olago, D., Owen, B., & Schabitz, F. (2014, Fall). The Hominin Sites and Paleolakes Drilling Project (HSPDP) drilling campaigns: the trials and triumphs of trying the unique and new. GSA Annual Meeting. Vancouver, BC Canada.
- Cohen, A. (2014, Fall). A 1.3 million year record of extraordinary climatic and ecological variability. AAAS Annual Meeting Symposium: The Evolving Great Lakes: New Techniques, Discoveries, and Management Implications. Chicago, IL.
- Cohen, A. S. (2014, December). A review of new and anticipated high-resolution paleoclimate records from the East African Rift System and their implications for homiin evolution and demography. AGU Annual Meeting. San Francisco.
- Cohen, A. S. (2014, October). The geological, ecological and paleoclimatological significance of “exotic” continental ostracodes: Rick Forester’s legacy in understanding ostracode evolution in long-lived lakes. GSA Annual Meeting. Vancouver.
- Cohen, A. S., Kingston, J., Kingston, J., Deino, A., Hill, A., & Cohen, A. S. (2014, Fall). Linking hominin evolution and climate in the Baringo Basin, Kenya: The Hominin Sites and Paleolakes Drilling Project (HSPDP). Society for Vertebrate Paleontology. Berlin, Germany: SVP.
- Feibel, C. S., Van Der Lubbe, J., Yost, C., Beck, C., Vonhof, H., Joordens, J., & Cohen, A. S. (2014, March). An integrated multi-proxy investigation of outcrop and core records from an Early Pleistocene lacustrine sequence in West Turkana, Kenya.. GSA Northeastern Section. Lancaster PA.
- Ivory, S., Lezzine, A., Vincens, A., & Cohen, A. S. (2014, December). Waxing and waning of forests: Late Quaternary Biogeography of Lake Malawi, Southeast Africa. AGU Annual Meeting. San Francisco.
- Lund, S., Platzman, E., Johnson, T., Scholz, C., Cohen, A. S., & Russell, J. (2014, December). Full vector Holocene paleomagnetic secular variation records from East Africa. AGU Annual Meeting. San Francisco.
- McCartney, T., Scholz, C., & Cohen, A. S. (2014, October). Correlations between natural spectral gamma and magnetic susceptibility logs at Kenyan HSPDP sites: The search for a magnetic susceptibility proxy. GSA Annual Mtg. Vancouver.
- Sier, M., Langereis, C., Dupont-Nivet, G., Joordens, J., Yost, C., Beck, C., Feibel, C., van der Lubbe, J., & Cohen, A. S. (2014, April). ICDP Hominin Sites and Paleolakes Drilling Project, an Introduction. NAC12 (Dutch Geology Congress). Veldhoven, Netherlands.
- Cohen, A. S., Lupien, R., Russell, J., Castaneda, I., & Campisano, C. (2017, Spring). Leaf wax biomarker reconstruction of Pliocene hydrological variation during Australopithecus afarensis evolution in Afar, Ethiopia core. PAGES 5th Open Science Meeting. Zaragoza, Spain: PAGES.
- Gravina, A., Cohen, A. S., Soreghan, M. J., Somasundaram, R., & Ryan, E. (2017, October). Impacts of excess sediment discharge from hillslope deforestation on populations of ostracodes on two platforms in Lake Tanganyika, Tanzania. GSA National Meeting. Seattle, WA: GSA.
- Chaudhary, M., Rabideaux, N., Deocampo, D., Feibel, C. S., & Cohen, A. S. (2016, Spring). Reconstructing Paleoenvironmental Conditions from Hydrothermally Altered Lacustrine Sediments from HSPDP West Turkana-Kaitio Core Material via Coupled Mineralogical and Geochemical Analysis .. Southeast Section-Geological Society of America. Columbia, SC: GSA.
- Cohen, A. S., Junginger, A., Vonhof, H., Foerster, V., Asrat, A., Lamb, H., Schaebitz, F., & Trauth, M. (2016, December). How wet is wet? Strontium isotopes as paleo-lake level indicators in the Chew Bahir basin (S-Ethiopia).. American Geophysical Union Annual Meeting. San Francisco, CA: AGU.
- Cohen, A. S., Leet, K., Lowenstein, T., Owen, R. B., Deocampo, D., McNulty, E., Muiruri, V., Rabideaux, N., & Billingsley, A. (2016, Fall). Origins of Magadi-type chert: New clues from the HSPDP Lake Magadi drill cores.. Geological Society of America Annual Meeting. Denver, CO: GSA.
- Foerster, V., Asrat, A., Cohen, A. S., Junginger, A., Lamb, H., Schaebitz, F., Trauth, M., & Vogelsang, R. (2016, December). How Dry was too Dry? Evaluating the Impact of Climatic Stress on Prehistoric Human Populations in southern Ethiopia. American Geophysical Union Annual Meeting. San Francisco, CA: AGU.
- James, B., Soreghan, M., De Beurs, K., McGlue, M., Kimerei, I., & Cohen, A. S. (2016, September). The enigmatic quaternary shell bed deposits of Lake Tanganyika, Tanzania: a story of anthropogenic or environmental change?. Geological Society of America Annual Meeting. Denver, CO: GSA.
- Minkara, K., Rabideaux, N., Deocampo, D., & Cohen, A. S. (2016, Fall). Minerals as climate change proxies: a paleoenvironmental interpretation of the BTB Tugen Hills drill core; part of the Hominin Sites and Paleolakes Drilling Project.. Geological Society of America Annual Meeting. Denver, CO: GSA.
- Minkara, K., Rabideaux, N., Deocampo, D., Kingston, J., & Cohen, A. S. (2016, December). Paleoenvironmental Interpretation of drill core from Tugen Hills, Kenya through X-ray Diffraction. American Geophysical Union Annual Meeting. San Francisco, CA: AGU.
- Minkara, K., Rabideaux, N., Deocampo, D., Kingston, J., & Cohen, A. S. (2016, Spring). Minerals as Climate Change Proxies: Developing a Paleoenviornmental Interpretation of the BTB Tugen Hills Drill Core: Part of the Hominin Sites and Paleolakes Drilling Project. Southeast Section- Geological Society of America. Columbia, S.C.: GSA.
- Beck, C. C., Feibel, C., Hendek, R. L., Cohen, A. S., Campisano, C., & Team members, H. (2015, June). A facies interpretation of the Hominin Sites and Paleolakes Drilling Project West Turkana core: Dynamic fluctuations on a shallow lacustrine margin.. VIth International Limnogeology Congress. Reno, NV: International Association of Limnogeology.
- Billingsley, A., Cohen, A. S., Kingston, J., Deino, A., Hill, A., Ortiz, K., & Plange, K. (2015, June). Time series analysis of the HSPDP drill core from the Tugen Hills, Kenya to determine effects of external forcing on local climate in the context of hominin evolution. VIth International Limnogeology Congress. Reno, NV: International Association of Limnogeology.
- Dean, J., Asrat, A., Cohen, A. S., Foerster, V., Just, J., Lamb, H., Leng, M., Schabitz, F., Trauth, M., & Viehberg, F. (2015, October). New Stable Isotope Record From Chew Bahir, Ethiopia Covering Past 100ka.. Geological Society of America Annual Meeting. Baltimore, MD: GSA.
- Foerster, V., Asrat, A., Cohen, A. S., Junginger, A., Gromig, R., Lamb, H., Schabitz, F., Trauth, M., & Science Team, H. (2015, June). Toward a half million year environmental record from the HSPDP deep drilling project in Chew Bahir, southern Ethiopia. VIth International Limnogeology Congress. Reno, NV: International Association of Limnogeology.
- Ivory, S., Blome, M., Cohen, A. S., McGlue, M., Lezzine, A., Lyons, R., Scholz, C., & King, J. (2015, June). Quaternary hydroclimatic and ecological change at Lake Malawi, Southeast Africa. VIth International Limnogeology Congress. Reno, NV: International Association of Limnogeology.
- Lowenstein, T., Renaut, R., Owen, R. B., Deocampo, D., Cohen, A. S., McNulty, E., Muiruri, V., Rabideaux, N., Billingsley, A., & Mbuthia, A. (2015, June). The sedimentary and paleoenvironmental history of Lake Magadi, Southern Kenya Rift: New evidence from drill cores in the axial graben. VIth International Limnogeology Congress. Reno, NV: International Association of Limnogeology.
- Montanye, B., Hartwel, A., Cohen, A. S., McKay, J., Severmann, S., & McManus, J. (2015, December). Changes in Biological Production and Lake Chemistry in Lake Tanganyika over the Past 400 Years. American Geophysical Union Annual Meeting. San Francisco, CA: AGU.
- Ortiz, K., Arrowsmith, R., Cohen, A. S., Feibel, C., Deino, A., Hill, A., Beck, C., Campisano, C., Valachovic, J., & Kingston, J. (2015, October). Paleoclimate And Paleoenvironmental Forcing On Early Humans: Loi Analysis Of Three HSPDP Drill Core Sites In Kenya And Ethiopia. Geological Society of America Annual Meeting. Baltimore, MD: GSA.
- Rabideaux, N., Deocampo, D., Potts, R., Behrensmeyer, A. K., Lowenstein, T., Renaut, R., Owen, R. B., & Cohen, A. S. (2015, June). Zeolitic alteration in saline, alkaline paleolake basins in the southern Kenya Rift as evidenced by analysis of minerals from Koora Graben (ODP) and Lake Magadi (HSPDP) core samples. Vith International Limnogeology Congress. Reno, NV: International Association of Limnogeology.
- Schabitz, F., Asrat, A., Lamb, H., Trauth, M., Foerster, V., Junginger, A., Raub, T., Gromig, R., Viehberg, F., Roberts, H., Cohen, A. S., & Science Team, H. (2015, December). Chew Bahir: A Key Site within the Hominin Sites and Paleolakes Drilling Project, towards a Half Million-Year Climate Record from Southern Ethiopia. American Geophysical Union Annual Meeting. San Francisco, CA: AGU.
- Stockhecke, M., Beck, C., Brown, E., Cohen, A. S., Deino, A., Feibel, C., & Drilling Project Team, H. (2015, December). A~600 kyr duration Early Pleistocene record from the West Turkana (Kenya) HSPDP drill site: elemental XRF variability to reconstruct climate change in Turkana Boy’s backyard. American Geophysical Union Annual Meeting. San Francisco, CA: AGU.
- Stockhecke, M., Behrensmeyer, A. K., Brown, E., Cohen, A. S., Deino, A., Dommain, R., Potts, R., & Research Team, O. (2015, June). Scanning x-ray fluorescence results from a ~1 Ma paleoenvironmental record adjacent to the Olorgesailie archaeological sites (Kenya). VIth International Limnogeology Congress. Reno, NV: International Association of Limnogeology.
- Yost, C., Cohen, A. S., & Feibel, C. (2015, June). Using phytoliths to reconstruct paleolimnological and terrestrial vegetation history at orbital time scales from the Early Pleistocene West Turkana, Kenya, drill core of the Hominin Sites and Paleolakes Drilling Project (HSPDP). VIth International Limnogeology Congress. Reno, NV: International Association of Limnogeology.
- van der Lubbe, J., Sier, M., Feibel, C., Beck, C., Dupont-Nivet, G., Vonhof, H., Joordens, J., Cohen, A. S., Prins, M. A., & Olago, D. (2015, December). Sr isotope stratigraphy and lithogenic grain-size distributions of the Pleistocene Turkana Basin, Kenya. American Geophysical Union Annual Meeting. San Francisco, CA: AGU.
- Jackson, L., Stone, J., & Cohen, A. S. (2014, December). Fine resolution analysis of Lake Malawi sediment record shows no significant climatic impacts from the Mount Toba Super-Eruption of ~75ky.. AGU Annual Meeting. San Francisco.
- Mitsunaga, B. A., Mering, J., Dunbar, R., Liu, X., Cohen, A. S., Kaufman, D., Eagle, R., & Tripati, A. (2014, October). A clumped isotope calibration for lacustrine carbonates. GSA Annual Mtg. Vancouver.
- Ortiz, K., Plange, K., Cohen, A. S., Feibel, C., Kingston, J., Deino, A., Hill, A., & Smith, P. (2014, October). Preliminary TOC/TIC and geophysical data from two HSPDP drill core sites in Kenya, with implications for Pliocene hominin paleoenvironments. GSA Annual Mtg. Vancouver.
- Stockhecke, M., Brown, E., Campisano, C., & Cohen, A. S. (2014, September). Future insights into East African continental climate variability and human evolution over 3.5 Ma: the Hominin Sites and Paleolakes Drilling Project (HSPDP), Multiproxy approach to the reconstruction of the Pliocene climate. ICREA Workshop. Barcelona, Spain.
- Yost, C., & Cohen, A. S. (2014, December). Phytoliths used to investigate the effects of the Indonesian Mount Toba Super-Eruption (~75kyr) in East Africa: A subdecadal record from Lake Malawi.. AGU Annual Meeting. San Francisco.
- Yost, C., Cohen, A. S., Feibel, C., & Campisano, C. (2014, October). Preliminary phytolith results from the early Pleistocene West Turkana, Kenya, drill core of the Hominin Sites and Paleolakes Drilling Project (HSPDP). GSA Ann Mtg. Vancouver.
- Cohen, A., & Team, H. R. (2013, Fall). The Hominin Sites And Paleolakes Drilling Project: A progress report on documenting the paleoenvironmental context of human origins through scientific drilling. East African Quaternary Assoc. Nanyuki, Kenya.
- Cohen, A., Arrowsmith, R., Asrat, A., Campisano, C., Deino, A., Feibel, C., Foerster, V., Hill, A., Ivory, S., Kingston, J., Lamb, H., Lowenstein, T., Olago, D., Owen, R., Renaut, R., Schäbitz, F., & Team, H. R. (2013, Fall). The Hominin Sites And Paleolakes Drilling Project (HSPDP): A progress report on documenting the paleoenvironmental context of human origins through scientific drilling. International Continental Drilling Program Science Conference 2013. Potsdam, Germany.
- Cohen, A., Asrat, A., Campisano, C., Feibel, C., Ivory, S., Kingston, J., Lamb, H., Olago, D., Renaut, R., Scahbitz, F., & team, H. f. (2013, Fall). The Hominin Sites and Paleolakes Drilling Project (HSPDP): Documenting the paleoenvironmental context of human origins in East Africa through scientific drilling. GSA Ann. Mtg. Denver, CO.More infoPages: 327-10
- Dorsey, R., Crossey, L., Cohen, A., Howard, K., Karlstrom, K., Bright, J., Homan, M., McDougall, K., & Retallack, G. (2013, Fall). Lake-Estuary Hypothesis For The Bouse Formation: New Look At An Old Problem. GSA Ann. Mtg. Denver, CO.More infoPages: 97-96
- Ivory, S., McGlue, M., Ellis, G., Lézine, A., Cohen, A., & Vincens, A. (2013, Fall). Vegetation controls on weathering intensity in southeast Africa. AGU Ann. Mtg. San Francisco, CA.
- Joordens, J., Feibel, C., Dupont-Nivet, G., Cohen, A., Beck, C., van, d., Sier, M., Langereis, C., & Vonhof, H. (2013, Fall). Combining the HSPDP West Turkana core with outcrop samples to provide a climate framework for hominin evolution between ca. 2.1 - 1.4 Ma. International Continental Drilling Program Science Conference 2013. Potsdam, Germany.
- McGlue, M., Ellis, G., Cohen, A., & Kowler, A. (2013, Fall). Integrated stratigraphic analysis and petroleum source-rock potential of an underfilled lake basin in the Puna Plateau (Northwestern Argentina). GSA Ann. Mtg. Denver, CO.More infoPages: 137-139
- McGlue, M., Ivory, S., Ellis, G., Boehlke, A., Blome, M., Cohen, A., Lyons, R., & Scholz, C. (2013, Fall). On climate, weathering, and siliciclastic sedimentation in tropical lacustrine rift basins. AAPG Ann. Meeting.
- Smith, P., McGlue, M., Zani, H., Carrapa, B., & Cohen, A. (2013, Fall). The modern Rio Bermejo Megafan, Chaco Foreland Basin (Argentina). GSA Ann. Mtg. Denver, CO.More infoPages: 247-263
- Cohen, A., & Blome, M. (2012, Fall). A ~1.25Ma continuous record of ostracode paleoecology from the African tropics at Lake Malawi. GSA Ann Mtg. Charlotte, NC.
- Cohen, A. S. (2017, April). The Fate of Africa’s Lake Tanganyika Hangs in the Balance.. The Conversation. https://theconversation.com/the-fate-of-africas-lake-tanganyika-lies-in-the-balance-75467More infoOn line news magazine op-ed