J Warren Beck
- Research Scientist, Physics
- Research Scientist, Geosciences
- Ph.D. Geochemistry
- University of Minnesota, Minneapolis, Minnesota, United States
- Implications for early Proterozoic tectonics and the origin of continental flood basalts, based on combined trace element and Neodymium/Strontium isotopic studies of mafic igneous rocks of the Penokean Lake Superior belt, Minnesota, Wisconsin and Michigan.
- B.S. Geology/geophysics
- University of Minnesota, Minneapolis, Minnesota, United States
- University of Arizona, Tucson, Arizona (1993 - Ongoing)
No activities entered.
Independent StudyPHYS 499 (Spring 2016)
- Beck, J. W., Zhou, W., Li, C., Wu, Z., White, L., Xian, F., Kong, X., & An, Z. (2018). A 550,000-year record of East Asian monsoon rainfall from 10Be in loess. Science, 360, 877-881.More infoThis work shows how changes in the shape of the Earth's orbit have influenced Asian Monsoon dynamics via modulation of the low latitude interhemispheric solar insolation gradient. Our work reveals that this gradient likely controls Asian Monsoon strength by modulating the pattern of upper tropospheric outflow from the Asian Monsoons to the North Pacific vs. Southern Indian Ocean subtropical highs. In so doing it also regulates the relative strength of Hadley and Walker circulations in the Indo-Pacific sectors. This in turn influences the relative strength of the Indian and Western North Pacific summer monsoons by influencing Trade Wind velocity in these two sectors through angular momentum export. We also show how Asian Monsoon coupling to Trade and Westerly Winds can influences export of heat and ocean salinity to the high northern Atlantic region, affecting the Atlantic Meridional Overturning Circulation (AMOC), which strongly influences the buildup or decay of northern Hemisphere ice sheets. Based on these findings we propose that the conventional Milankovitich model of high northern latitude orbital forcing of glacial/interglacial climate may by incomplete. Instead, we suggest that the Asian Monsoon intensity and dynamics--controlled by low latitude interhemispheric insolation gradient, not high northern latitude insolation-- may be the dominant mechanism for control of planetary scale glacial/interglacial cycles in climate. .
- Burr, G. S., Haynes, V., Shen, C., Taylor, F., Chang, Y., Beck, J. W., Nguyen, V., & Zhou, W. (2015). Temporal variations of radiocarbon reservoir age in the South PAcific ocean during the Holocene. Radiocarbon, 57(4), 507-515. doi:10.2458/azu_rc.57.18460More infoThis article discusses the magnitude and rate of change of radiocarbon reservoir ages from the surface ocean in the South Pacific during the Holocene. C-14 reservoir ages are calculated from paired U/Th and C-14 measurements. Seventeen pairs of coral dates were determined from samples collected on Rendova and Tetepare Islands, in the Solomon Islands, and from Espiritu Santo Island, Vanuatu. The samples are all Holocene in age, with Th-230 ages ranging from about 400 to 9400 BP. Samples were collected as drill cores or surface outcrops. About half of the surface samples appear to have incorporated modern carbon through postdepositional recrystallization. Two of the core samples were also affected by carbon exchange. The Holocene C-14 reservoir ages observed in this data set show stable values for the last 3000 yr, and substantial variability from 5000-6000 BP (similar to 100 to similar to 950 C-14 yr). Persistent low values (
- Feng, T., Zhou, W., Beck, J. W., Du, Y., & Sha, L. (2015). Spatiotemporal relationship between temperature and precipitation in inland China from meteorological data and paleoclimatic implications for lacustrine oxygen records.. Quaternary International, 349, 291-299.More infodiscussion of factors controlling climate in China's western interior using oxygen isotope record patterns and principal components analysis.
- Feng, T., Zhou, W., Beck, W., Du, Y., & Sha, L. (2015). Spatiotemporal relationship between temperature and precipitation in inland China from meteorological data and paleoclimatic implications for lacustrine oxygen records. QUATERNARY INTERNATIONAL, 349, 291-299.More infoThe factors controlling climate in China's western interior are numerous and quite complex. These vary on seasonal to multi-millennial time scales as a result of changing dominance of influence from the Westerlies and the Asian and Indian Monsoon systems. These in turn respond to additional factors such as the dynamics of the Walker and Hadley circulation in the Pacific and Indian Ocean basins, the strength of the Siberian and Northwest Pacific Highs, and on long timescales to changes in the distribution of solar insolation resulting from orbital forcing. Here, we use the Empirical Orthogonal Function (EOF) analysis to investigate the spatiotemporal patterns of climate in China's western interior during the last 15 ka as revealed from a suite of 17 lacustrine carbonate delta O-18 records. Based on similarities to the EOF analysis of the modern data, we interpret the first two leading eigenmodes of the paleodata sets as P and T, respectively. Other climatic proxy data from this region appear to agree well with this interpretation. Our analysis reveals a discrete change in the spatial EOF patterns occurring at circa 7.5-6 ka BP with respect to the patterns observed prior to this. These patterns suggest that the arid NW region of the study area became significantly wetter following this juncture, but that the Asian Monsoon influenced (SE) region of the study area along the eastern flank of the Tibetan Plateau became drier. A more complex pattern of change is revealed by the second rank EOF, interpreted as temperature. This shows a discrete change at similar to 7.5-6 ka BP from cooler to hotter temperatures on the central Tibetan Plateau, but slightly cooler temperatures in the lowland Monsoon affected area (SE) after 6 ka BP. We interpret both these sets of changes to result from more persistent high pressure over the Tibetan Plateau during Boreal summer, with a resultant enhancement of moisture transport by the westerlies and diminished monsoonal flow following similar to 6 ka BP. (C) 2014 Elsevier Ltd and INQUA. All rights reserved.
- Gnanaprakasa, T., Gu, Y., Eddy, S., Han, Z., Beck, J. W., Muralidharan, K., & Raghavan, S. (2015). The role of copper pretreatment on the morphology of graphene grown by chemical vapor deposition. Microelectronics Engineering, 131, 1-7.
- Gnanaprakasa, T., Sridhar, D., Beck, J. W., Runge, K., Potter, B., Zega, T., Deymier, P., Raghavan, S., & Muralidharan, K. (2015). Graphene mediated self-assembly of fullerene nanorods.. Chemical Communications, 51, 1858-1861. doi:10.1039/C4CC09362C
- Trzaskowski, B., Adamowicz, L., Beck, W., Muralidharan, K., & Deymier, P. A. (2015). Impact of Local Curvature and Structural Defects on Graphene-C-60 Fullerene Fusion Reaction Barriers. JOURNAL OF PHYSICAL CHEMISTRY C, 117(38), 19664-19671.More infoSelf-consistent charge density functional tight-binding and density functional theory calculations have been employed to study the energetics of the graphene-C-60 fullerene fusion. We show that there is an optimal value of the bond-puckering angle of single-layer graphene-like systems, which facilitates fusion with other low-dimension carbon systems. Specifically, chemical attachment of a C-60 fullerene to a single-layer graphene sheet is not feasible from the energetic point of view due to lack of puckering of the pristine graphene surface, but may occur for systems with some surface curvature. The presence of various defects in the graphene surface, including formation of four- and five-membered rings, Stone-Wales defects, or single and double vacancies may create some surface strain leading to formation of reactive sites in graphene, which are susceptive to binding with a fullerene. As an example, we show that a single vacancy in the graphene surface can lead to formation of a stable chemical bond with a fullerene.
- Zhou, W., Xie, X., Beck, W., Kong, X., Xian, F., Du, Y., & Wu, Z. (2015). Recent progress of Be-10 tracer studies in Chinese loess. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 361, 548-553.
- Beck, J. W., Trzaskowski, B., Adamowicz, L., Beck, W., Muralidharan, K., & Deymier, P. (2014). Exploring structures and properties of new geodesic polyarenes. Chemical Physics Letters, 595-596, 6-12.
- Beck, J. W., Weijian, Z., Beck, W., Xianghui, K., Zhisheng, A., Xiaoke, Q., Zhenkin, W., Feng, X., & Ho, A. (2014). Timing of the Brunhes/Matuyama magnetic polarity reversal in Chinese Loess using 10Be. Geology, 42, 467-470.More infodoi:10.1130/G35443.1
- Gnanaprakasa, T. J., Sridhar, D., Beck, W. J., Runge, K., Potter, B. G., Zega, T. J., Deymier, P. A., Raghavan, S., & Muralidharan, K. (2015). Graphene mediated self-assembly of fullerene nanorods. CHEMICAL COMMUNICATIONS, 51(10), 1858-1861.More infoA simple procedure for solution-based self-assembly of C-60 fullerene nanorods on graphene substrates is presented. Using a combination of electron microscopy, X-ray diffraction and Raman spectroscopy, it is shown that the size, shape and morphology of the nanorods can be suitably modified by controlling the kinetics of self-assembly.
- Kong, X., Zhou, W., Beck, J., Xian, F., & Wu, Z. (2014). Asynchronous records of Brunhes/Matuyama reversal in marine sediments and Chinese loess: Review and discussion. Quaternary International, 319, 137-142.
- Beck, J. W., Laref, S., Asaduzzaman, A., Beck, W., Deymier, P., Runge, K., Adamowicz, L., & Muralidharan, K. (2013). Characterization of graphene-fullerene interactions: Insights from density functional theory. Chemical Physics Letters, 582, 115-118.
- Beck, J. W., Trzaskowski, B., Adamowicz, L., Beck, W., Muralidharan, K., & Deymier, P. (2013). Impact of Local Curvature and Structural Defects on Graphene-C60 Fullerene Fusion Reaction Barriers. The Journal of Physical Chemistry, Part C, 117(38), 19664-19671.
- Burr, G. S., Donahue, D. J., Tang, Y., Beck, J. W., McHargue, L., Biddulph, D., Cruz, R., & Jull, A. J. (2013). Error analysis at the NSF-Arizona AMS facility. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 259(1), 149-153.More infoThis article presents a detailed explanation of the analytical method used to monitor and quantify measurement uncertainties at the NSF-Arizona Accelerator Mass Spectrometry (AMS) Laboratory. The method is applicable to all of the isotopes measured at the facility, including C-14, Be-10, I-129 and Al-26. It is used for a variety of analytical purposes, including: calculation of random machine error (rme), calculation of radiocarbon dates, and as an indicator of daily and long-term machine performance. An algorithm for a diagnostic program used to monitor rme is described in detail. The performance of the AMS machine as measured by rme calculations is given for the most recent six month period. The long-term accuracy of the machine is discussed in terms of blind sample analyses made under the Third (TIRI), Fourth (FIRI) and Fifth (VIRI) International Radiocarbon Intercomparisons. (c) 2007 Elsevier B.V. All rights reserved.
- EDWARDS, R., BECK, J., BURR, G., DONAHUE, D., CHAPPELL, J., BLOOM, A., DRUFFEL, E., & TAYLOR, F. (1993). A LARGE DROP IN ATMOSPHERIC C-14/C-12 AND REDUCED MELTING IN THE YOUNGER DRYAS, DOCUMENTED WITH TH-230 AGES OF CORALS. SCIENCE, 260(5110), 962-968.More infoPaired carbon-14 (C-14) and thorium-230(Th-230) ages were determined on fossil corals from the Huon Peninsula, PaPua New Guinea. The ages were used to calibrate part of the C-14 time scale and to estimate rates of sea-level rise during the last deglaciation. An abrupt offset between the C-14 and Th-230 ages suggests that the atmospheric C-14/C-12 ratio dropped by 15 percent during the latter part of and after the Younger Dryas (YD). This prominent drop coincides with greatly reduced rates of sea-level rise. Reduction of melting because of cooler conditions during the YD may have caused an increase in the rate of ocean ventilation, which caused the atmospheric C-14/C-12 ratio to fall. The record of sea-level rise also shows that globally averaged rates of melting were relatively high at the beginning of the YD. Thus, these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the Mississippi to the St. Lawrence River triggered the YD event.
- Reimer, P., Bard, E., Bayliss, A., Beck, J., Blackwell, P., Ramsey, C., Brown, D., Buck, C., Edwards, R., Friedrich, M., Grootes, P., Guilderson, T., Hafildason, H., Hajdas, I., Hatté, C., Heaton, T., Hogg, A., Hughen, K., Kaiser, K., , Kromer, B., et al. (2013). IntCal13 and Marine13 Radiocarbon Age Calibration curves 0-50,000 Years cal BP. Radiocarbon, 55(4), 1869-1887.
- Reimer, P., Bard, E., Bayliss, A., Beck, J., Blackwell, P., Ramsey, C., Brown, D., Buck, C., Edwards, R., Friedrich, M., Grootes, P., Guilderson, T., Hafildason, H., Hajdas, I., Hatté, C., Heaton, T., Hogg, A., Hughen, K., Kaiser, K., , Kromer, B., et al. (2013). Selection and treatment of data for radiocarbon calibration: An update to the international calibration (IntCal) criteria. Radiocarbon, 55(4), 1-23.
- Trzaskowski, B., Adamowicz, L., Beck, W., Muralidharan, K., & Deymier, P. A. (2013). Exploring structures and properties of new geodesic polyarenes. CHEMICAL PHYSICS LETTERS, 595, 6-12.More infoWe have employed the self-consistent charge density-functional tight-binding, the density functional theory and the classical molecular dynamics methods to study new geodesic polyarenes, which can be synthesized via the regiospecific cove-region closure and HF elimination. We show that the shape of new polyarenes may be altered and controlled by the presence of C-60 fullerenes. The high intrinsic curvature of the geodesic arenes facilitates fusion with C-60 fullerenes. This propensity to fuse is consistent with the hypothesis of an optimal value of the bond-puckering angle at which graphene-like structures show maximum reactivity. (C) 2014 Elsevier B.V. All rights reserved.
- Xian Feng, ., An ZhiSheng, ., Wu ZhenKun, ., Beck, J. W., Yu HuaGui, ., Kang ZhiHai, ., & Cheng Peng, . (2013). A simple model for reconstructing geomagnetic field intensity with (10)Be production rate and its application in Loess studies. SCIENCE IN CHINA SERIES D-EARTH SCIENCES, 51(6), 855-861.More infoA simple model for reconstructing the paleomagnetic field intensity with (10)Be production rate was used for the first time in Loess (10)Be studies of Luochuan profile. Using the LGM (Last Glacial Maxmium) method, the climatic effects and geomagnetic modulation effects on loess (10)Be was separated and in turn the 80 ka geomagnetic excursion sequence reconstructed, of which the globally remarkable geomagnetic excursion events such as the Laschamp (42 ka), Mono Lake (32 ka) during the Last Glacial period were revealed and the paleo-geomagnetic intensity curve from Loess (10)Be over the past 80 ka was quantitatively reconstructed. The reconstructed paleo-intensity fits well with the paleo-intensity curves (SINT200 and NAPIS75), which indicates the significance of global criterion of the (10)Be paleo-intensity curve and the future direction of loess (10)Be tracing studies. Results show the irregular variability of the East Asian monsoon precipitation in Loess Plateau is the main cause that has resulted in the ambiguity of the geomagnetic modulation of the (10)Be record in the loess, and the intrinsic source component of the loess (10)Be and inherited fraction of magnetic susceptibility (SUS) are characterized by the "quasi-homogeneous distribution" manner.
- Shanahan, T., Beck, J., Overpeck, J., McKay, N., Pigati, J., Peck, J., Scholz, C., & King, J. (2012). Late Quaternary sedimentological and climate changes at Lake Bosumtwi Ghana: new constraints from laminae analysis and radiocarbon age modeling. Paleogeography, Paleoclimatology, Paleoecology, 361-362, 49-60.
- Reimer, P. J., Bard, E., Bayliss, A., Beck, J. W., Blackwell, P. G., Ramsey, C. B., Buck, C. E., Cheng, H., Edwards, R. L., Friedrich, M., Grootes, P. M., Guilderson, T. P., Haflidason, H., Hajdas, I., Hatte, C., Heaton, T. J., Hoffmann, D. L., Hogg, A. G., Hughen, K. A., , Kaiser, K. F., et al. (2011). INTCAL13 AND MARINE13 RADIOCARBON AGE CALIBRATION CURVES 0-50,000 YEARS CAL BP. RADIOCARBON, 55(4), 1869-1887.More infoThe IntCal09 and Marine09 radiocarbon calibration curves have been revised utilizing newly available and updated data sets from C-14 measurements on tree rings, plant macrofossils, speleothems, corals, and foraminifera. The calibration curves were derived from the data using the random walk model (RWM) used to generate IntCal09 and Marine09, which has been revised to account for additional uncertainties and error structures. The new curves were ratified at the 21st International Radiocarbon conference in July 2012 and are available as Supplemental Material at www.radiocarbon.org. The database can be accessed at http://intcal.qub.ac.uk/intcal13/.
- Robillard, J., Muralidharan, K., Deymier, P., Beck, J., & Barker, D. (2011). Phononic metamaterials for thermal management: an atomistic computational study. Chinese J. Physics, 49(1), 448-461.
- BECK, J., JASZCZAK, R., COLEMAN, R., STARMER, C., & NOLTE, L. (2010). ANALYSIS OF SPECT INCLUDING SCATTER AND ATTENUATION USING SOPHISTICATED MONTE-CARLO MODELING METHODS. IEEE TRANSACTIONS ON NUCLEAR SCIENCE, 29(1), 506-511.
- BREIMAN, R., BECK, J., KOROBKIN, M., GLENNY, R., AKWARI, O., HEASTON, D., MOORE, A., & RAM, P. (2010). VOLUME DETERMINATIONS USING COMPUTED-TOMOGRAPHY. AMERICAN JOURNAL OF ROENTGENOLOGY, 138(2), 329-333.
- MIN, G., EDWARDS, R., TAYLOR, F., RECY, J., GALLUP, C., & BECK, J. (2010). ANNUAL CYCLES OF U/CA IN CORAL SKELETONS AND U/CA THERMOMETRY. GEOCHIMICA ET COSMOCHIMICA ACTA, 59(10), 2025-2042.More infoWe have discovered annual variations in the U-238/Ca-40 ratio of Porites coral skeletons. Measurements were made using thermal ionization mass spectrometric techniques, yielding precisions of +/-2 parts per thousand (2 sigma) for U-238/Ca-40 and +/-1 parts per thousand (2 sigma) for Sr-88/Ca-40. Coralline aragonite subsamples weighed similar to 2 mg, enabling submillimeter sampling resolution corresponding to similar to monthly temporal resolution. The annual nature of the cycles was confirmed by comparison with annual banding observable in X-radiographs. For two modern and one fossil sample, the amplitude of the U/Ca variation ranges from 6 to 23%, well outside of analytical error. As annual U/Ca cycles appear to be a general feature of primary coralline aragonite, the preservation of such features will be important in identifying unaltered coral for U-series dating studies. U/Ca variations mimic and are in phase with annual variations in Sr-88/Ca-40. For given fractional shift in Sr/Ca, the fractional shift in U/Ca is about 6 times larger. For the two modem corals, U-238/Ca-40 is strongly anticorrelated with measured temperature, suggesting that U-238/Ca-40 has potential as a paleothermometer. If temperature is the only significant control on coralline U-238/Ca-40, We reach the following conclusions from analyses of fossil samples: a Vanuatu sample, which grew halfway through the last deglaciation, gives U/Ca temperatures 4 to 5 degrees C below modern values. U/Ca thermometry applied to published data for Barbados corals indicates that (1) temperature generally correlates with sea level, (2) glacial temperatures (stages 2 and 4) were 4 to 6 degrees C lower than interglacial temperatures (stages 7a, 5e, and 1), and (3) temperatures rose from glacial to interglacial values early in the last deglaciation. Thermometry applied to Papua New Guinea corals indicates that (1) temperatures were 5 to 6 degrees C lower than interglacial temperatures from similar to 13 to similar to 10 Ky BP, then rose to present values similar to 9 Ky BP, (2) the temperature depression between similar to 13 and similar to 10 Ky BP is consistent with low temperatures observed in Vanuatu during the same time interval, and (3) the Papua New Guinea deglacial temperature history differs from that of Barbados. The results generally support estimates of tropical temperatures obtained from Sr/Ca thermometry and snow line elevation data, but disagree with those based on foram transfer functions. A thermodynamic model suggests that coralline U-238/Ca-40 may also be sensitive to marine carbonate ion concentration, raising the possibility that some of the observed glacial-interglacial U-238/Ca-40 variation may result from glacial-interglacial carbonate ion changes. However, the key experiments that might establish a coralline U-238/Ca-40-carbonate ion relationship have yet to be performed.
- Reimer, P. J., Bard, E., Bayliss, A., Beck, J. W., Blackwell, P. G., Ramsey, C. B., Brown, D. M., Buck, C. E., Edwards, R. L., Friedrich, M., Grootes, P. M., Guilderson, T. P., Haflidason, H., Hajdas, I., Hatte, C., Heaton, T. J., Hogg, A. G., Hughen, K. A., Kaiser, K. F., , Kromer, B., et al. (2010). SELECTION AND TREATMENT OF DATA FOR RADIOCARBON CALIBRATION: AN UPDATE TO THE INTERNATIONAL CALIBRATION (INTCAL) CRITERIA. RADIOCARBON, 55(4), 1923-1945.More infoHigh-quality data from appropriate archives are needed for the continuing improvement of radiocarbon calibration curves. We discuss here the basic assumptions behind C-14 dating that necessitate calibration and the relative strengths and weaknesses of archives from which calibration data are obtained. We also highlight the procedures, problems, and uncertainties involved in determining atmospheric and surface ocean C-14/C-12 in these archives, including a discussion of the various methods used to derive an independent absolute timescale and uncertainty. The types of data required for the current IntCal database and calibration curve model are tabulated with examples.
- BECK, J., EDWARDS, R., ITO, E., TAYLOR, F., RECY, J., ROUGERIE, F., JOANNOT, P., & HENIN, C. (2009). SEA-SURFACE TEMPERATURE FROM CORAL SKELETAL STRONTIUM CALCIUM RATIOS. SCIENCE, 257(5070), 644-647.More infoSeasonal records of tropical sea-surface temperature (SST) over the past 10(5) years can be recovered from high-precision measurements of coral strontium/calcium ratios with the use of thermal ionization mass spectrometry. The temperature dependence of these ratios was calibrated with corals collected at SST recording stations and by O-18/O-16 thermometry. The results suggest that mean monthly SST may be determined with an apparent accuracy of better than 0.5-degrees-C. Measurements on a fossil coral indicate that 10,200 years ago mean annual SSTs near Vanuatu in the southwestern Pacific Ocean were about 5-degrees-C colder than today and that seasonal variations in SST were larger. These data suggest that tropical climate zones were compressed toward the equator during deglaciation.
- Jull, A., Burr, G., Beck, J., Donahue, D., Biddulph, D., Hatheway, A., Lange, T., & McHargue, L. (2009). Accelerator mass spectrometry at Arizona: geochronology of the climate record and connections with the ocean. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY, 69(1-2), 3-19.More infoThere are many diverse uses of accelerator mass spectrometry (AMS). Carbon-14 studies at our laboratory include much research related to paleoclimate, both with C-14 as a tracer of past changes in environmental conditions as observed in corals, marine sediments and many terrestrial records. Terrestrial records such as forest fires can also show the influence of oceanic oscillations, whether they are short-term such as ENSO, or on the millennial time scale. In tracer applications, we have developed the use of I-129 as well as C-14 as tracers for nuclear pollution studies around radioactive waste dump sites, in collaboration with IAEA. We discuss some applications carried out in Tucson for several of these fields and hope to give some idea of the breadth of these studies. (C) 2003 Elsevier Science Ltd. All rights reserved.
- Shanahan, T. M., Beck, J. W., Overpeck, J. T., Mckay, N. P., Pigati, J. S., Peck, J. A., Scholz, C. A., Heil, C. W., & King, J. (2009). Late Quaternary sedimentological and climate changes at Lake Bosumtwi Ghana: New constraints from laminae analysis and radiocarbon age modeling. PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY, 361, 49-60.More infoThe Lake Bosumtwi sediment record represents one of the longest and highest-resolution terrestrial records of paleoclimate change available from sub-Saharan Africa. Here we report a new sediment age model framework for the last similar to 45 cal kyr of sedimentation using a combination of high-resolution radiocarbon dating, Bayesian age-depth modeling and lamination counting. Our results highlight the practical limits of these methods for reducing age model uncertainties and suggest that even with very high sampling densities, radiocarbon uncertainties of at least a few hundred years are unavoidable. Age model uncertainties are smallest during the Holocene (205 yr) and the glacial (360 yr) but are large at the base of the record (1660 yr), due to a combination of decreasing sample density, larger calibration uncertainties and increases in radiocarbon age scatter. For portions of the chronology older than similar to 35 cal kyr, additional considerations, such as the use of a low-blank graphitization system and more rigorous sample pretreatment were necessary to generate a reliable age depth model because of the incorporation of small amounts of younger carbon. A comparison of radiocarbon age model results and lamination counts over the time interval similar to 15-30 cal kyr agree with an overall discrepancy of similar to 10% and display similar changes in sedimentation rate, supporting the annual nature of sediment laminations in the early part of the record. Changes in sedimentation rates reconstructed from the age-depth model indicate that intervals of enhanced sediment delivery occurred at 16-19,24 and 29-31 cal kyr, broadly synchronous with reconstructed drought episodes elsewhere in northern West Africa and potentially, with changes in Atlantic meridional heat transport during North Atlantic Heinrich events. These data suggest that millennial-scale drought events in the West African monsoon region were latitudinally extensive, reaching within several hundred kilometers of the Guinea coast. This is inconsistent with a simple southward shift in the mean position of the monsoon rainbelt, and requires changes in moisture convergence as a result of either a reduction in the moisture content of the tropical rainbelt, decreased convection, or both. (C) 2012 Elsevier BM. All rights reserved.
- BERNDT, M., SEYFRIED, W., & BECK, J. (1988). HYDROTHERMAL ALTERATION PROCESSES AT MIDOCEAN RIDGES - EXPERIMENTAL AND THEORETICAL CONSTRAINTS FROM CA AND SR EXCHANGE-REACTIONS AND SR ISOTOPIC-RATIOS. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH AND PLANETS, 93(B5), 4573-4583.
- Beck, J., Recy, J., Taylor, F., Edwards, R., & Cabioch, G. (2008). Abrupt changes in early Holocene tropical sea surface temperature derived from coral records. NATURE, 385(6618), 705-707.More infoFor many high-latitude regions of the globe, it is now clear that the transition to modern climate following the Last Glacial Maximum was punctuated by a number of rapid and substantial climate oscillations(1,2). In contrast, relatively little is known about how the tropics responded to the deglaciation, because few high-resolution records are available from lower latitudes. Corals have recently been shown to provide an important source of tropical climate records because they can be easily and accurately dated, using either C-14 or Th-230, and because past sea surface temperatures can be recovered from the Sr/Ca ratios in coral skeletons. Here we use this technique to derive several early Holocene sea surface temperature records from a coral drill core recovered from Espiritu Santo, Vanuatu in the tropical southwest Pacific Ocean. These records indicate that sea surface temperatures in this region were depressed by as much as 6.5 degrees C below modern values at similar to 10,350 calendar years BP, but rose very abruptly during the following 1,500 years. This temperature increase lags the post-Younger Dryas increase observed in a coral record from the tropical Atlantic Ocean(3) by about 3,000 years, an unexpected phase-shift that may ultimately shed light on the mechanisms of deglacial climate change.
- Biddulph, D., Beck, J., Burr, G., Donahue, D., Hatheway, A., & Jull, A. (2008). Measurement of the radioisotope I-129 at the NSF-Arizona AMS laboratory. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 172, 693-698.More infoWith the recent addition of a high-energy analysis beam line, the capability to measure I-129 has been developed at the NSF-Arizona AMS Laboratory. Preliminary measurements have been made using the +4 and +5 charge states at 2.1 MV with a gas stripper. The current system employs a 90 degrees injection magnet (r = 0.36 m) following the ion source. Analysis components following the accelerator include an electrostatic quadrupole doublet lens, a 15 degrees electrostatic deflector (r = 1.25 m), a 90 degrees analysis magnet (r = 1.27 m) and a 77 degrees spherical electrostatic analyzer (r = 2.0 m). Detection of I-129 is accomplished with a silicon surface barrier detector. Operation of this system with Various iodine samples will be discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
- Gnanaprakasa, T. J., Gu, Y., Eddy, S. K., Han, Z., Beck, W. J., Muralidharan, K., & Raghavan, S. (2008). The role of copper pretreatment on the morphology of graphene grown by chemical vapor deposition. MICROELECTRONIC ENGINEERING, 131, 1-7.More infoThe effect of pretreatment of copper on the ensuing morphology and surface coverage of graphene grown using chemical vapor deposition (CVD) has been investigated. Specifically, graphene grown on electropolished copper (EP-Cu) was analyzed with respect to its surface morphology, surface roughness and thickness, and compared with graphene grown on as cold-rolled acetic acid cleaned copper (AA-Cu). Results show an improvement in the quality of graphene obtained using EP-Cu over AA-Cu. Additionally, electrochemical polarization studies were performed on annealed and graphene coated EP-Cu in acidic solutions. The results indicate that corrosion inhibition of EP-Cu is possible through the use of graphene films. (C) 2014 Elsevier B.V. All rights reserved.
- Grumet, N., Abram, N., Beck, J., Dunbar, R., Gagan, M., Guilderson, T., Hantoro, W., & Suwargadi, B. (2008). Coral radiocarbon records of Indian Ocean water mass mixing and wind-induced upwelling along the coast of Sumatra, Indonesia. JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 109(C5).More info Radiocarbon (C-14) in the skeletal aragonite of annually banded corals track radiocarbon concentrations in dissolved inorganic carbon (DIC) in surface seawater. As a result of nuclear weapons testing in the 1950s, oceanic uptake of excess C-14 in the atmosphere has increased the contrast between surface and deep ocean C-14 concentrations. We present accelerator mass spectrometric (AMS) measurements of C-14/C-12 ratios (Delta(14)C) in Porites corals from the Mentawai Islands, Sumatra (0degreesS, 98degreesE) and Watamu, Kenya (3degreesS, 39degreesE) to document the temporal and spatial evolution of the C-14 zonal gradient in the tropical Indian Ocean. The rise in Delta(14)C in the Sumatra coral, in response to the maximum in nuclear weapons testing, is delayed by 2-3 years relative to the rise in coral Delta(14)C from the coast of Kenya. Kenya coral Delta(14)C values rise quickly because surface waters are in prolonged contact with the atmosphere. In contrast, wind-induced upwelling and rapid mixing along the coast of Sumatra entrains C-14-depleted water from the subsurface, which dilutes the effect of the uptake of bomb-produced C-14 by the surface ocean. Bimonthly AMS Delta(14)C measurements on the Mentawai coral reveal mainly interannual variability with minor seasonal variability. Singular spectrum analysis of the Sumatra coral Delta(14)C record reveals a significant 3-year periodicity. These results lend support to the concept that interannual variability in Indian Ocean upwelling and sea surface temperatures is related to ENSO-like teleconnections over the Indo-Pacific basin.
- Jull, A. J., Burr, G. S., Beck, J. W., Hodgins, G. W., Biddulph, D. L., McHargue, L. R., Lange, T. E., & Povinec, P. (2008). Accelerator mass spectrometry of long-lived light radionuclides. ANALYSIS OF ENVIRONMENTAL RADIONUCLIDES, 11, 241-262.More infoMany different kinds of paleoclimatic, geological and archaeological records can be characterized by measuring their radionuclide concentrations using accelerator mass spectrometry (AMS). The purpose of this paper is to highlight some applications of AMS, using studies conducted at the Arizona AMS Facility as examples. These include studies of C-14, Be-10, Al-26, and I-129. The work can be generally divided into two types: (1) methodological studies designed to refine and improve the capabilities of AMS, and (2) studies which utilize radiogenic isotopes as geochronometers or as geochemical tracers. Studies of the first type include the development of our Al-26 measurement capabilities, the construction on an automated sample preparation line and the construction of a plasma oxidation line. Studies of the latter type include C-14 dating of corals, speleothems and bones; new records of Be-10 from marine sediments and extraterrestrial materials; and I-129 studies of the pathways of this isotope in the surface ocean.
- Mann, D., Edwards, J., Chase, J., Beck, W., Reanier, R., Mass, M., Finney, B., & Loret, J. (2008). Drought, vegetation change, and human history on Rapa Nui (Isla de Pascua, Easter Island). QUATERNARY RESEARCH, 69(1), 16-28.More infoStratigraphic records from lake sediment cores and slope deposits on Rapa Nui document prehistoric human impacts and natural environmental changes. A hiatus in sedimentation in Rano Raraku suggests that this lake basin dried out sometime after 4090-4410 cal yr BP and refilled only decades to centuries before AD 1180-1290. Widespread ecosystem changes caused by forest clearance by Polynesian farmers began shortly after the end of this drought. Terrestrial sections show a chronology of burning and soil erosion similar to the lake cores. Although changing sediment types and shifts in the pollen rain suggest that droughts occurred earlier in the Holocene, as yet there is no evidence for droughts occurring after AD 1180-1290. The timing of the agricultural colonization of Rapa Nui now seems well established at ca. AD 1200 and it was accompanied by rapid deforestation that was probably exacerbated by the island's small size, its droughty climate, and the rarity of primeval fires. Detailed records of a large interval of Rapa Nui's ecological history remain elusive due to the drought hiatus in the Rano Raraku sediment record. We find no evidence for a "rat outbreak impact" on Rapa Nui's vegetation preceding anthropogenic forest clearance. (C) 2007 University of Washington. All rights reserved.
- Taylor, F., Mann, P., Bevis, M., Edwards, R., Cheng, H., Cutler, K., Gray, S., Burr, G., Beck, J., Phillips, D., Cabioch, G., & Recy, J. (2008). Rapid forearc uplift and subsidence caused by impinging bathymetric features: Examples from the New Hebrides and Solomon arcs. TECTONICS, 24(6).More infoIsotopically dated corals from the central New Hebrides and New Georgia Island Group, Solomon Islands, indicate that both forearcs underwent rapid late Quaternary subsidence that was abruptly replaced by hundreds of meters of uplift at rates up to similar to 8 mm/yr, while total plate convergence was only a few kilometers. Two mechanisms that might account for these rapid reversals in vertical motion include (1) a "displacement'' mechanism in which the forearc is displaced upward by the volume of an object passing beneath on the subducting plate (as the object moves deeper and vacates the base of the forearc, the forearc subsides to near its original position) and (2) a "crustal shortening'' mechanism in which the forearc thickens and uplifts because of horizontal shortening when a large object impinges on the forearc and abruptly increases interplate coupling on the shallow end of the main thrust zone. Rapid subsidence follows when the impinging object is broken or otherwise decoupled, shallow interplate coupling becomes weak, and the uplifted forearc extends and subsides. The displacement mechanism surely plays a role on timescales over which plates converge tens of kilometers, but it fails to explain the geographic pattern, short time frame, and abruptness of the change from subsidence to uplift that we observe. The crustal shortening mechanism is preferred because it allows the observed abrupt uplift when an object impinges on a forearc and causes locking of a shallow segment of the interplate thrust zone.
- Zhou, W., Beck, J. W., Kong, X., An, Z., Qiang, X., Wu, Z., Xian, F., & Ao, H. (2007). Timing of the Brunhes-Matuyama magnetic polarity reversal in Chinese loess using Be-10. GEOLOGY, 42(6), 467-470.More infoIn Chinese loess, the Brunhes-Matuyama (B-M) geomagnetic reversal occurs similar to 25 k.y. prior to the age found in marine sediments. This offset has been attributed by some to post-depositional magnetic overprinting of loess, while others have argued it is due to errors in the loess time scale. Here we solve this long-standing debate by exploiting a new method to extract reproducible records of geomagnetic field intensity from loess with Be-10-a proxy for global average geomagnetic field intensity-and using it to show that a pronounced minimum in field intensity (a requirement for dipole field reversal) is recorded in two separate loess records at ca. 780 +/- 3 kyr B. P. This timing is synchronous with the B-M reversal timing seen in marine records, verifying the standard loess time scale as correct, but it is similar to 25 k.y. younger than the age (depth) of the magnetic polarity reversal recorded in these same Chinese loess sediments, demonstrating that loess magnetic overprinting has occurred.
- Jull, A., Lal, D., Burr, G., Bland, P., Bevan, A., & Beck, J. (2006). Radiocarbon beyond this world. RADIOCARBON, 42(1), 151-+.More infoIn this paper we review the production of radiocarbon and other radionuclides in extraterrestrial materials. This radioactivity can be produced by the effects of solar and galactic cosmic rays on solid material in space. In addition, direct implantation at the lunar surface of C-14 and other radionuclides can occur. The level of C-14 and other radionuclides in a meteorite can be used to determine its residence time on the Earth's surface, or "terrestrial age". C-14 provides the best tool for estimating terrestrial ages of meteorites collected in desert environments. Age control allows us to understand the time constraints on processes by which meteorites are weathered, as well as mean storage times. Third, we discuss the use of the difference in C-14/C-12 ratio of organic material and carbonates produced on other planetary objects and terrestrial material. These differences can be used to assess the importance of distinguishing primary material formed on the parent body from secondary alteration of meteoritic material after it lands on the earth.
- Burr, G., Beck, J., Taylor, F., Recy, J., Edwards, R., Cabioch, G., Correge, T., Donahue, D., & O'Malley, J. (2005). A high-resolution radiocarbon calibration between 11,700 and 12,400 calendar years BP derived from Th-230 ages of corals from Espiritu Santo Island, Vanuatu. RADIOCARBON, 40(3), 1093-1105.More infoThis paper presents radiocarbon results from a single Diploastrea heliopora coral from Vanuatu that lived during the Younger Dryas climatic episode, between ca. 11,700 and 12,400 calendar yr sp. The specimen has been independently dated with multiple Th-230 measurements to permit calibration of the C-14 time scale. Growth bands in the coral were used to identify individual years of growth. C-14 measurements were made on each year. These values were averaged to achieve decadal resolution for the C-14 calibration. The relative uncertainty of the decadal C-14 data was below 1% (2 sigma). The data are in good agreement with the existing dendrochronology and allow for hi,oh-resolution calibration for most years. Variations in the fine structure of the C-14 time series preserved in this specimen demonstrate sporadic rapid increases in the Delta(14)C content of the surface ocean and atmosphere. Certain sharp rises in Delta(14)C are coincident with gaps in coral growth evidenced by several hiatuses. These may be related to rapid climatic changes that occurred during the Younger Dryas. This is the first coral calibration with decadal resolution and the only such data set to extend beyond the dendrochronology-based C-14 calibration.
- Singarayer, J. S., Richards, D. A., Ridgwell, A., Valdes, P. J., Austin, W. E., & Beck, J. W. (2005). An oceanic origin for the increase of atmospheric radiocarbon during the Younger Dryas. GEOPHYSICAL RESEARCH LETTERS, 35(14).More infoVariations in carbon-14 to carbon-12 ratio in the atmosphere (Delta C-14(atm)) provide a powerful diagnostic for elucidating the timing and nature of geophysical and anthropological change. The ( Atlantic) marine archive suggests a rapid Delta C-14(atm) increase of 50% at the onset of the Younger Dryas (YD) cold reversal (12.9-11.7 kyr BP), which has not yet been satisfactorily explained in terms of magnitude or causal mechanism, as either a change in ocean ventilation or production rate. Using Earth-system model simulations and comparison of marine-based radiocarbon records from different ocean basins, we demonstrate that the YD Delta C-14(atm) increase is smaller than suggested by the marine archive. This is due to changes in reservoir age, predominantly caused by reduced ocean ventilation.
- Zhou, W., Xian, F., Beck, J. W., Jull, A. J., An, Z., Wu, Z., Liu, M., Chen, M., Priller, A., Kutschera, W., Burr, G. S., Yu, H., Song, S., Cheng, P., & Kong, X. (2005). RECONSTRUCTION OF 130-KYR RELATIVE GEOMAGNETIC INTENSITIES FROM Be-10 IN TWO CHINESE LOESS SECTIONS. RADIOCARBON, 52(1), 129-147.More infoEfforts to extract weak geomagnetic excursion signals from Chinese loess-paleosol Be-10 have generally been unsuccessful due to the complexities of its accumulation, because the geomagnetic and climate (precipitation and dust) signals contained in loess-paleosol sequence are tightly overprinted. Here, we present a reconstruction of geomagnetic relative paleointensities for the past 130 kyr from Be-10 records in 2 Chinese loess-paleosol sections using a correction based on the correlation of Be-10 with magnetic susceptibility (SUS) to remove the climatic contamination. Both these records reveal the Laschamp and Blake events, which lie in the loess and paleosol (L1SS1 and S1SS3) horizons corresponding to mid-MIS 3 and 5e, respectively. The good agreement between our results and other geomagnetic intensities reconstructions from Atlantic and Pacific sediments indicates that our method is robust. Our study suggests the potential application of loess-paleosol Be-10 for reconstructing geomagnetic intensity variations spanning the whole Quaternary.
- BECK, J., BERNDT, M., & SEYFRIED, W. (2004). APPLICATION OF ISOTOPIC DOPING TECHNIQUES TO EVALUATION OF REACTION-KINETICS AND FLUID MINERAL DISTRIBUTION COEFFICIENTS - AN EXPERIMENTAL-STUDY OF CALCITE AT ELEVATED-TEMPERATURES AND PRESSURES. CHEMICAL GEOLOGY, 97(1-2), 125-144.More infoIsotopic doping techniques have been combined with flexible cell hydrothermal equipment to evaluate the kinetics of calcite recrystallization at elevated temperatures and pressures. Two "free-drift" experiments were performed with a fluid/calcite mass ratio of 15, using Iceland spar calcite as the starting solid and a 0.5 m NaCl fluid of variable pH and total dissolved carbon. The first experiment was conducted at 250-degrees-C and 500 bar with a starting fluid near calcite saturation, while a second experiment was conducted at a series of temperature steps of 300-degrees, 350-degrees and 400-degrees-C and 500 bar, with a fluid chemistry initially adjusted to be far from calcite saturation.
- Beck, J., Richards, D., Edwards, R., Silverman, B., Smart, P., Donahue, D., Hererra-Osterheld, S., Burr, G., Calsoyas, L., Jull, A., & Biddulph, D. (2004). Extremely large variations of atmospheric C-14 concentration during the last glacial period. SCIENCE, 292(5526), 2453-2458.More infoA long record of atmospheric C-14 concentration, from 45 to 11 thousand years ago (ka), was obtained from a stalagmite with thermal-ionization mass-spectrometric Th-230 and accelerator mass-spectrometric C-14 measurements. This record reveals highly elevated Delta C-14 between 45 and 33 ka, portions of which may correlate with peaks in cosmogenic Cl-36 and Be-10 isotopes observed in polar ice cores. Superimposed on this broad peak of Delta C-14 are several rapid excursions, the Largest of which occurs between 44.3 and 43.3 ka. Between 26 and 11 ka, atmospheric Delta C-14 decreased from similar to 700 to similar to 100 per mil, modulated by numerous minor excursions. Carbon cycle models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone but also require substantial fluctuations in the carbon cycle.
- Jull, A., Beck, J., & Burr, G. (2004). Isotopic evidence for extraterrestrial organic material in the Martian meteorite, Nakhla. GEOCHIMICA ET COSMOCHIMICA ACTA, 64(21), 3763-3772.More infoIn this paper, we report on new C-14 and C-13 isotopic analyses of organic and carbonate phases in pristine samples of the martian meteorite, Nakhla (fell 1911AD). We undertook water and acid extractions of soluble phases as well as a study of insoluble material. We used 14C to differentiate between extraterrestrial organic material and recent terrestrial contamination. Results indicate that most of the organic matter in Nakhla is released by 6N HCl and there appear to be two isotopically distinct sources of extraterrestrial organics with delta C-13 Of -33 parts per thousand and -15 parts per thousand and low C-14. We estimate that at least 75% of the organic material released by 6N HCl acid etching is extraterrestrial. We conclude that this acid-labile component is likely similar to polymeric organics observed in CM2 chondrites (Gilmour and Pillinger, 1994) and could have accumulated on the Martian surface from the accumulation of meteoritic material and cometary debris and cosmic dust. We also determined that the terrestrial organic contamination is characterized by approximately modem C-14 values and delta C-13 of -25 parts per thousand. Copyright (C) 2000 Elsevier Science Ltd.
- Stuiver, M., Reimer, P., Bard, E., Beck, J., Burr, G., Hughen, K., Kromer, B., McCormac, G., Van der Plicht, J., & Spurk, M. (2004). INTCAL98 radiocarbon age calibration, 24,000-0 cal BP. RADIOCARBON, 40(3), 1041-1083.More infoThe focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the interval 24,000-0 cal BP (Before Present, 0 cal BP = AD 1950), based upon a sample set of dendrochronologically dated tree rings, uranium-thorium dated corals, and varve-counted marine sediment. The (14)C age-cal age information, produced by many laboratories, is converted to Delta(14)C profiles and calibration curves, for the atmosphere as well as the oceans. We discuss offsets in measured (14)C ages and the errors therein, regional (14)C age differences, tree-coral (14)C age comparisons and the time dependence of marine reservoir ages, and evaluate decadal vs. single-year (14)C results. Changes in oceanic deepwater circulation, especially for the 16,000-11,000 cal sp interval, are reflected in the Delta(14)C values of INTCAL98.
- Zhou, W., Priller, A., Beck, J. W., Wu Zhengkun, ., Chen Maobai, ., An Zhisheng, ., Kutschera, W., Feng, X., Yu Huagui, ., & Lin, L. (2004). Disentangling geomagnetic and precipitation signals in an 80-Kyr Chinese loess record of Be-10. RADIOCARBON, 49(1), 139-160.More infoThe cosmogenic radionuclide Be-10 is produced by cosmic-ray spallation in Earth's atmosphere. Its production rate is regulated by the geomagnetic field intensity, so that its accumulation rate in aeolian sediments can, in principle, be used to derive high-resolution records of geomagnetic field changes. However, Be-10 atmospheric fallout rate also varies locally depending on rainfall rate. The accumulation rate of I Be in sediments is further complicated by overprinting of the geomagnetic and precipitation signals by Be-10 attached to remobilized dust, which fell from the atmosphere at some time in the past. Here, we demonstrate that these signals can be deconvoluted to derive both geomagnetic field intensity and paleoprecipitation records of Asian Monsoon intensity in an 80,000-yr-long Be-10 record from Chinese loess. The strong similarity between our derived paleomagnetic intensity record and the SINT 200 (Guyodo and Valet 1996) and NAPIS 75 (Laj et al. 2002) stacked-marine records suggests that this method might be used to produce multimillion-yr-long records of paleomagnetic intensity from loess. This technique also reveals a new method for extracting quantitative paleoprecipitation records from continental interior regions. Our derived precipitation record is broadly similar to the speleothem delta O-18-based records of paleo-Asian Monsoon intensity from Dongge (Yuan et al. 2004) and Hulu (Wang et al. 2001) caves, and suggests that the paleo-Asian Monsoon intensity may be responding to a combination of both Northern and Southern Hemisphere insulation forcing.
- Hoffmann, D. L., Beck, J. W., Richards, D. A., Smart, P. L., Singarayer, J. S., Ketchmark, T., & Hawkesworth, C. J. (2003). Towards radiocarbon calibration beyond 28 ka using speleothems from the Bahamas. EARTH AND PLANETARY SCIENCE LETTERS, 289(1-2), 1-10.More infoWe present a new speleothem record of atmospheric Delta(14)C between 28 and 44 ka that offers considerable promise for resolving some of the uncertainty associated with existing radiocarbon calibration curves for this time period. The record is based on a comprehensive suite of AMS (14)C ages, using new low-blank protocols, and U-Th ages using high precision MC-ICPMS procedures. Atmospheric Delta(14)C was calculated by correcting (14)C ages with a constant dead carbon fraction (DCF) of 22.7 +/- 5.9%, based on a comparison of stalagmite (14)C ages with the lntCal04 (Reimer et al., 2004) calibration curve between 15 and 11 ka. The new Delta(14)C speleothem record shows similar structure and amplitude to that derived from Cariaco Basin foraminifera (Hughen et al., 2004, 2006), and the match is further improved if the latter is tied to the most recent Greenland ice core chronology (Svensson et al., 2008). These data are however in conflict with a previously published (14)C data set for a stalagmite record from the Bahamas - CB-89-24-1 (Beck et al., 2001), which likely suffered from (14)C analytical blank subtraction issues in the older part of the record. The new Bahamas speleothem. Delta(14)C data do not show the extreme shifts between 44 and 40 ka reported in the previous study (Beck et al., 2001). Causes for the observed structure in derived atmospheric Delta(14)C variation based on the new speleothem data are investigated with a suite of simulations using an earth system model of intermediate complexity. Data-model comparison indicates that major fluctuations in atmospheric Delta(14)C during marine isotope stage 3 is primarily a function of changes in geomagnetic field intensity, although ocean-atmosphere system reorganisation also played a supporting role. (C) 2009 Elsevier B.V. All rights reserved.
- Zaunbrecher, L. K., Cobb, K. M., Beck, J. W., Charles, C. D., Druffel, E. R., Fairbanks, R. G., Griffin, S., & Sayani, H. R. (2002). Coral records of central tropical Pacific radiocarbon variability during the last millennium. PALEOCEANOGRAPHY, 25.More infoThe relationship between decadal to centennial changes in ocean circulation and climate is difficult to discern using the sparse and discontinuous instrumental record of climate and, as such, represents a large uncertainty in coupled ocean-atmosphere general circulation models. We present new modern and fossil coral radiocarbon (Delta(14)C) records from Palmyra (6 degrees N, 162 degrees W) and Christmas (2 degrees N, 157 degrees W) islands to constrain central tropical Pacific ocean circulation changes during the last millennium. Seasonally to annually resolved coral Delta(14)C measurements from the 10th, 12th-17th, and 20th centuries do not contain significant interannual to decadal-scale variations, despite large changes in coral delta(18)O on these timescales. A centennial-scale increase in coral radiocarbon from the Medieval Climate Anomaly (similar to 900-1200 AD) to the Little Ice Age (similar to 1500-1800) can be largely explained by changes in the atmospheric Delta(14)C, as determined with a box model of Palmyra mixed layer Delta(14)C. However, large 12th century depletions in Palmyra coral Delta(14)C may reflect as much as a 100% increase in upwelling rates and/or a significant decrease in the Delta(14)C of higher-latitude source waters reaching the equatorial Pacific during this time. SEM photos reveal evidence for minor dissolution and addition of secondary aragonite in the fossil corals, but our results suggest that coral Delta(14)C is only compromised after moderate to severe diagenesis for these relatively young fossil corals.
- Jull, A., Burr, G., McHargue, L., Lange, T., Lifton, N., Beck, J., Donahue, D., & Lal, D. (2001). New frontiers in dating of geological, paleoclimatic and anthropological applications using accelerator mass spectrometric measurements of C-14 and Be-10 in diverse samples. GLOBAL AND PLANETARY CHANGE, 41(3-4), 309-323.More infoA wide range of climatic, geologic and archeological records can be characterized by measuring their C-14 and Be-10 concentrations, using the accelerator mass spectrometry (AMS). These records are found not only in the traditional sampling sites such as lake sediments and ice cores, but also in diverse natural accumulates and biogeochemical products such as: loess/ paleosol deposits, corals, speleothems, forest-fire horizons and weathered meteorites. The in-situ production of cosmogenic radionuclides in terrestrial materials provides several possibilities of determining their chronology. The purpose of this review is to highlight selected applications of AMS, which have bearing to our understanding of both chronology of archival materials, and learning about climatic changes in the past. (C) 2004 Elsevier B.V. All rights reserved.
- Jull, A., Courtney, C., Jeffrey, D., & Beck, J. (2001). Isotopic evidence for a terrestrial source of organic compounds found in martian meteorites Allan Hills 84001 and Elephant Moraine 79001. SCIENCE, 279(5349), 366-369.More infoStepped-heating experiments on martian meteorites Allan Hills 84001 (ALH84001) and Elephant Moraine 79001 (EETA79001) revealed low-temperature (200 to 430 degrees Celsius) fractions with a carbon isotopic composition delta(13)C between -22 and -33 per mil and a carbon-14 content that is 40 to 60 percent of that of modern terrestrial carbon, consistent with a terrestrial origin for most of the organic material. Intermediate-temperature (400 to 600 degrees Celsius) carbonate-rich fractions of ALH84001 have delta(13)C of +32 to 140 per mil with a low carbon-14 content, consistent with an extraterrestrial origin, whereas some of the carbonate fraction of EETA79001 is terrestrial, In addition, ALH84001 contains a small preterrestrial carbon component of unknown origin that combusts at intermediate temperatures. This component is likely a residual acid-insoluble carbonate or a more refractory organic phase.
- Shanahan, T. M., Overpeck, J. T., Beck, J. W., Wheeler, C. W., Peck, J. A., King, J. W., & Scholz, C. A. (2001). The formation of biogeochemical laminations in Lake Bosumtwi, Ghana, and their usefulness as indicators of past environmental changes. JOURNAL OF PALEOLIMNOLOGY, 40(1), 339-355.More infoThe sediments from Lake Bosumtwi, Ghana contain a unique record of fine-scale (mm to sub-mm) laminations, which will provide a valuable annual chronometer for reconstructing paleoenvironmental changes in West Africa covering much of the last 1 Ma. Comparisons of laminae counts to independent (210)Pb dates and the rise in anthropogenic "bomb" radiocarbon support the interpretation of the laminations in the uppermost sediments as registering annual events. Radiocarbon dates on in-situ fish-bone collagen are in agreement with varve counts, further supporting the annual nature of our varve chronology. Over the instrumental period (1925-1999), dark-varve thickness measurements are correlated with local rainfall (r = 0.54) and appear able to resolve decadal-scale changes in precipitation. The relationship between varve thickness and rainfall provides support for our interpretation that dark-colored varve thickness records catchment runoff during the rainy season rather than dust flux during the dry season. Dark laminae alternate with organic and carbonate-rich light laminae formed during the fall period of enhanced productivity. Downcore, varves undergo significant microstratigraphic and geochemical variations, but retain the same pattern of alternating clastic and organic-rich laminae, providing support that the laminae may represent annual time markers for reconstructions of the deeper part of the record.
- Burr, G. S., Beck, J. W., Correge, T., Cabioch, G., Taylor, F. W., & Donahue, D. J. (2000). MODERN AND PLEISTOCENE RESERVOIR AGES INFERRED FROM SOUTH PACIFIC CORALS. RADIOCARBON, 51(1), 319-335.More infoThis paper presents radiocarbon results from modern South Pacific corals from the Marquesas Islands, Vanuatu. Papua New Guinea (PNG), and Easter Island. All of the measurements are from pre-bomb Porites corals that lived during the 1940s and 1950s. The data reflect subannual to multiannual surface ocean (14)C variability and allow for precise. unambiguous reservoir age determinations. The results are compared with published values from other coral records throughout the South Pacific, with striking consistency. By comparisons with other published values, we identify 3 South Pacific regions with uniform pre-bomb reservoir ages (1945 to 1955). These are I) the Central Equatorial South Pacific (361.6 +/- 8.2 (14)C yr. 2 sigma); 2) the Western Equatorial South Pacific (322.1 +/- 8.6 (14)C yr, 2 sigma): and 3) the subtropical Pacific (266.8 +/- 13.8 (14)C yr, 2 sigma).
- Correge, T., Gagan, M., Beck, J., Burr, G., Cabioch, G., & Le Cornec, F. (2000). Interdecadal variation in the extent of South Pacific tropical waters during the Younger Dryas event. NATURE, 428(6986), 927-929.More infoDuring the Younger Dryas event, about 12,000 years ago, the Northern Hemisphere cooled by between 2 and 10 degreesC (refs 1, 2) whereas East Antarctica experienced warming(3). But the spatial signature of the event in the southern mid-latitudes and tropics is less well known, as records are sparse and inconclusive(4-16). Here we present high-resolution analyses of skeletal Sr/Ca and O-18/O-16 ratios for a giant fossil Diploastrea heliopora coral that was preserved in growth position on the raised reef terraces of Espiritu Santo Island, Vanuatu, in the southwestern tropical Pacific Ocean(17). Our data indicate that sea surface temperatures in Vanuatu were on average 4.5 +/- 1.3 degreesC cooler during the Younger Dryas event than today, with a significant interdecadal modulation. The amplified annual cycle of sea surface temperatures, relative to today, indicates that cooling was caused by the compression of tropical waters towards the Equator. The positive correlation in our record between the oxygen isotope ratios of sea water and sea surface temperatures suggests that the South Pacific convergence zone, which brings O-18-depleted precipitation to the area today, was not active during the Younger Dryas period.
- Shanahan, T. M., Overpeck, J. T., Anchukaitis, K. J., Beck, J. W., Cole, J. E., Dettman, D. L., Peck, J. A., Scholz, C. A., & King, J. W. (2000). Atlantic Forcing of Persistent Drought in West Africa. SCIENCE, 324(5925), 377-380.More infoAlthough persistent drought in West Africa is well documented from the instrumental record and has been primarily attributed to changing Atlantic sea surface temperatures, little is known about the length, severity, and origin of drought before the 20th century. We combined geomorphic, isotopic, and geochemical evidence from the sediments of Lake Bosumtwi, Ghana, to reconstruct natural variability in the African monsoon over the past three millennia. We find that intervals of severe drought lasting for periods ranging from decades to centuries are characteristic of the monsoon and are linked to natural variations in Atlantic temperatures. Thus the severe drought of recent decades is not anomalous in the context of the past three millennia, indicating that the monsoon is capable of longer and more severe future droughts.
- Short, M., Baygents, J., Beck, J., Stone, D., Toomey, R., & Goldstein, R. (2000). Stalactite growth as a free-boundary problem: A geometric law and its platonic ideal. PHYSICAL REVIEW LETTERS, 94(1).More infoThe chemical mechanisms underlying the growth of cave formations such as stalactites are well known, yet no theory has yet been proposed which successfully accounts for the dynamic evolution of their shapes. Here we consider the interplay of thin-film fluid dynamics, calcium carbonate chemistry, and CO2 transport in the cave to show that stalactites evolve according to a novel local geometric growth law which exhibits extreme amplification at the tip as a consequence of the locally-varying fluid layer thickness. Studies of this model show that a broad class of initial conditions is attracted to an ideal shape which is strikingly close to a statistical average of natural stalactites.
- Cutler, K., Gray, S., Burr, G., Edwards, R., Taylor, F., Cabioch, G., Beck, J., Cheng, H., & Moore, J. (1999). Radiocarbon calibration and comparison to 50 kyr BP with paired C-14 and Th-230 dating of corals from Vanuatu and Papua New Guinea. RADIOCARBON, 46(3), 1127-1160.More infoWe calibrated portions of the radiocarbon time scale with combined Th-230, Pa-231, C-14 measurements of corals collected from Espiritu Santo, Vanuatu and the Huon Peninsula, Papua New Guinea. The new data map C-14 variations ranging from the current limit of the tree-ring calibration (11,900 calendar years before present [cal BP], Kromer and Spark 1998, now updated to 12,400 cal BP, see Kromer et al., this issue), to the C-14-dating limit of 50,000 cal BP, with detailed structure between 14 to 16 cal kyr BP and 19 to 24 cal kyr BP. Samples older than 25,000 cal BP were analyzed with high-precision Pa-231 dating methods (Pickett et al. 1994; Edwards et al. 1997) as a rigorous second check on the accuracy of the Th-230 ages. These are the first coral calibration data to receive this additional check, adding confidence to the age data forming the older portion of the calibration. Our results, in general, show that the offset between calibrated and C-14 ages generally increases with age until about 28,000 cal BP, when the recorded C-14 age is nearly 6800 yr too young. The gap between ages before this time is less; at 50,000 cal BP, the recorded C-14 age is 4600 yr too young. Two major C-14-age plateaus result from a 130 parts per thousand drop in Delta(14)C between 14-15 cal kyr BP and a 700 parts per thousand drop in Delta(14)C between 22-25 cal kyr FIR In addition, a large atmospheric Delta(14)C excursion to values over 1000 parts per thousand occurs at 28 cal kyr BP. Between 20 and 10 cal kyr BP, a component of atmospheric Delta(14)C anti-correlates with Greenland ice 8180, indicating that some portion of the variability in atmospheric Delta(14)C is related to climate change, most likely through climate-related changes in the carbon cycle. Furthermore, the 28-kyr excursion occurs at about the time of significant climate shifts. Taken as a whole, our data indicate that in addition to a terrestrial magnetic field, factors related to climate change have affected the history of atmospheric C-14.
- Balch, D., Cohen, A., Schnurrenberger, D., Haskell, B., Garces, B., Beck, J., Cheng, H., & Edwards, R. (1998). Ecosystem and paleohydrological response to Quaternary climate change in the Bonneville Basin, Utah. PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY, 221(1-2), 99-122.More infoWe report the results of a detailed paleoecological study of the Bonneville basin covering the last similar to 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 similar to 1 in 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 C-14, 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. (c) 2005 Elsevier B.V. All rights reserved.
- Reimer, P., Baillie, M., Bard, E., Bayliss, A., Beck, J., Bertrand, C., Blackwell, P., Buck, C., Burr, G., Cutler, K., Damon, P., Edwards, R., Fairbanks, R., Friedrich, M., Guilderson, T., Hogg, A., Hughen, K., Kromer, B., McCormac, G., , Manning, S., et al. (1998). IntCal04 terrestrial radiocarbon age calibration, 0-26 cal kyr BP. RADIOCARBON, 46(3), 1029-1058.More infoA new calibration curve for the conversion of radiocarbon ages to calibrated (cal) ages has been constructed and internationally ratified to replace ImCal98, which extended from 0-24 cal kyr BP (Before Present, 0 cal BP = AD 1950). The new calibration data set for terrestrial samples extends from 0-26 cal kyr BP, but with much higher resolution beyond 11.4 cal kyr BP than ImCal98. Dendrochronologically-dated tree-ring samples cover the period from 0-12.4 cal kyr BP. Beyond the end of the tree rings, data from marine records (corals and foraminifera) are converted to the atmospheric equivalent with a site-specific marine reservoir correction to provide terrestrial calibration from 12.4-26.0 cal kyr BP. A substantial enhancement relative to ImCal98 is the introduction of a coherent statistical approach based on a random walk model, which takes into account the uncertainty in both the calendar age and the C-14 age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The tree-ring data sets, sources of uncertainty, and regional offsets are discussed here. The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine 04) are discussed in brief, but details are presented in Hughen et al. (this issue a). We do not make a recommendation for calibration beyond 26 cal kyr BP at this time; however, potential calibration data sets are compared in another paper (van der Plicht et al., this issue).
- Reimer, P., Hughen, K., Guilderson, T., McCormac, G., Baillie, M., Bard, E., Barratt, P., Beck, J., Buck, C., Damon, P., Friedrich, M., Kromer, B., Ramsey, C., Reimer, R., Remmele, S., Southon, ., Stuiver, M., & van der Plicht, J. (1998). Preliminary report of the first workshop of the IntCal04 radiocarbon calibration/comparison working group. RADIOCARBON, 44(3), 653-661.More infoThe first meeting of the IntCal04 working group took place at Queen's University Belfast from April 15 to 17, 2002. The participants are listed as co-authors of this report. The meeting considered criteria for the acceptance of data into the next official calibration dataset, the importance of including reliable estimates of uncertainty in both the radiocarbon ages and the cal ages, and potential methods for combining datasets. This preliminary report summarizes the criteria that were discussed, but does not yet give specific recommendations for inclusion or exclusion of individual datasets.
- van der Plicht, J., Beck, J., Bard, E., Baillie, M., Blackwell, P., Buck, C., Friedrich, M., Guilderson, T., Hughen, K., Kromer, B., McCormac, F., Ramsey, C., Reimer, P., Reimer, R., Remmele, S., Richards, D., Southon, ., Stuiver, M., & Weyhenmeyer, C. (1997). NotCal04 - Comparison/calibration C-14 records 26-50 cal kyr BP. RADIOCARBON, 46(3), 1225-1238.More infoThe radiocarbon calibration curve ImCal04 extends back to 26 cal kyr BP. While several high-resolution records exist beyond this limit, these data sets exhibit discrepancies of up, to several millennia. As a result, no calibration curve for the time range 26-50 cal kyr BP can be recommended as yet, but in this paper the IntCal04 working group compares the available data sets and offers a discussion of the information that they hold.
- Wagner, J. D., Cole, J. E., Beck, J. W., Patchett, P. J., Henderson, G. M., & Barnett, H. R. (1995). Moisture variability in the southwestern United States linked to abrupt glacial climate change. NATURE GEOSCIENCE, 3(2), 110-113.More infoMany regions of the world experienced abrupt climate variability during the last glacial period (75-15 thousand years ago(1,2)). These changes probably arose from interactions between Northern Hemisphere ice sheets and circulation in the North Atlantic Ocean(3), but the rapid and widespread propagation of these changes requires a large-scale atmospheric response whose details remain unclear(4-7). Here we use an oxygen isotope record from a speleothem collected from the Cave of the Bells, Arizona, USA, to reconstruct aridity in the southwestern United States during the last glacial period and deglaciation. We find that, during this period, aridity in the southwestern United States and climate in the North Atlantic region show similar patterns of variability. Periods of warmth in the North Atlantic Ocean, such as interstadials and the Bolling-Allerod warming, correspond to drier conditions in the southwestern United States. Conversely, cooler temperatures in the high latitudes are associated with increased regional moisture. We propose that interstadial warming of the North Atlantic Ocean diverted the westerly storm track northward, perhaps through weakening of the Aleutian Low, and thereby reduced moisture delivery to southwestern North America. A similar response to future warming would exacerbate aridity in this already very dry region.
- Zhou, W., Head, M., An, Z., De Deckker, P., Liu, Z., Liu, X., Lu, X., Donahue, D., Jull, A., & Beck, J. (1994). Terrestrial evidence for a spatial structure of tropical-polar interconnections during the Younger Dryas episode. EARTH AND PLANETARY SCIENCE LETTERS, 191(3-4), 231-239.More infoThe Younger Dryas chronozone, recognised in northern high-latitude areas as a cold event between 11 000 and 10 000 C-14 yr BP (12 900-11 600 cal. yr BP), seems to manifest itself globally in different ways. Here, we examine well-dated stratigraphic sequences together with high-resolution proxy data plots from sites across our study area, the arid-semi-arid transition zone in northern China. This climatically sensitive area of China records a cold, dry Younger Dryas climate which was punctuated by a brief period of summer monsoon precipitation. We have since found that similar climatic sequences have been reported from the Sahel and the equatorial region of Africa. Based on evidence from these sites, together with other published data, we postulate that precipitation during the Younger Dryas chronozone was indicative of a low-latitude driving force superimposed on the high-latitude cold background. This rain belt rearrangement was most probably caused by an interaction between cold air advection and summer moisture transport across the tropical Pacific Ocean. Examination of high-resolution proxies suggests short-term climate fluctuations indicative of a global teleconnection involving moist air transportation patterns from the tropics to higher latitudes, varying with ENSO and other tropical factors. (C) 2001 Elsevier Science B.V. All rights reserved.
- Donahue, D., Beck, J., Biddulph, D., Burr, G., Courtney, C., Damon, P., Hatheway, A., Hewitt, L., Jull, A., Lange, T., Lifton, N., Maddock, R., McHargue, L., OMalley, J., & Toolin, L. (1992). Status of the NSF-Arizona AMS Laboratory. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 123(1-4), 51-56.More infoThe operation of the NSF-Arizona Laboratory is summarized. The methods used to determine accuracy and precision of radiocarbon measurements, and to make corrections for background contaminations are presented. An insulating support which has been installed, and a new heavy-ion beam line which is under construction, are described.
- Hughen, K., Baillie, M., Bard, E., Beck, J., Bertrand, C., Blackwell, P., Buck, C., Burr, G., Cutler, K., Damon, P., Edwards, R., Fairbanks, R., Friedrich, M., Guilderson, T., Kromer, B., McCormac, G., Manning, S., Ramsey, C., Reimer, P., , Reimer, R., et al. (1992). Marine04 marine radiocarbon age calibration, 0-26 cal kyr BP. RADIOCARBON, 46(3), 1059-1086.More infoNew radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally ratified to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0-26 cal kyr BP (Before Present, 0 cal. BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0-10.5 call kyr BR Beyond 10.5 cal kyr BP, high-resolution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific C-14 reservoir age information to provide a single global marine mixed-layer calibration from 10.5-26.0 cal kyr BR A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the C-14 age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue).
- Gagan, M., Ayliffe, L., Beck, J., Cole, J., Druffel, E., Dunbar, R., & Schrag, D. (1988). New views of tropical paleoclimates from corals. QUATERNARY SCIENCE REVIEWS, 19(1-5), 45-64.More infoCorals offer a rich archive of past climate variability in tropical ocean regions where instrumental data are limited and where our knowledge of multi-decadal climate sensitivity is incomplete. In the eastern equatorial Pacific, coral isotopic records track variations in ENSO-related changes in sea-surface temperature; further west, corals record variability in sea-surface temperature and rainfall that accompanies zonal displacement of the Indonesian Low during ENSO events. These multi-century records reveal previously unrecognised ENSO variability on time scales of decades to centuries. Outside the ENSO-sensitive equatorial Pacific, long-term trends towards recent warmer/wetter conditions suggest the tropics respond to global forcings. New coral paleothermometers indicate that surface-ocean temperatures in the tropical southwestern Pacific were depressed by 4-6 degrees C during the Younger Dryas climatic event and rose episodically during the next 4000 yr. High temporal-resolution measurements of Sr/Ca and delta(18)O in corals provide information about the surface-ocean hydrologic balance and can resolve the seasonal balance between precipitation and evaporation. Radiocarbon measurements in corals, coupled with ocean circulation models, may be used to reconstruct near-surface ocean circulation, past mixing rates, and the distribution of fossil fuel CO2 in the upper ocean. Most recently, seasonal to interannual variations in the radiocarbon of corals from the equatorial Pacific have been linked to the redistribution of surface waters associated with the ENSO. (C) 1999 Elsevier Science Ltd. All rights reserved.
- Richards, D., & Beck, J. (1982). Dramatic shifts in atmospheric radiocarbon during the last glacial period. ANTIQUITY, 75(289), 482-485.
- Schmidt, A., Burr, G., Taylor, F., O'Malley, J., & Beck, J. (1982). A semiannual radiocarbon record of a modern coral from the Solomon Islands. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 223, 420-427.More infoRadiocarbon records from modern corals have long been recognized for their usefulness as a geochemical tracer of surface ocean waters and oceanic upwelling. Pacific corals are especially interesting because of their potential relevance to El Nino - Southern Oscillation (ENSO) events. At present, the Pacific Ocean is undersampled with respect to radiocarbon time series. This study establishes a C-14 time series for a coral from the Solomon Islands, located near the center of the Western Pacific Warm Pool (WPWP). We present radiocarbon results from a Porites colony which grew in Marau Sound, on the east coast of Guadalcanal. A semiannual record of C-14 was constructed from measurements of alternating bands which grew continuously from 1944 to 1994. The record reflects the uptake of atmospheric bomb-produced C-14 since the late 1950s with superimposed subannual radiocarbon variations, presumably related to changes in ocean circulation. Although the coral radiocarbon is influenced by ENSO events, the record is not closely correlated with the Southern Oscillation Index (Sol) for the same period. (C) 2004 Elsevier B.V. All rights reserved.
- Beck, J. W. (2013, December). Orbital forcing of Asian monsoon rainfall based on 10Be in Chinese loess. American Geophysical Union meeting. San Francisco, CA.
- Beck, J. W. (2012, June). Extracting quantitative rainfall and geomagnetic intensity records from Chinese Loess using 10Be and magnetic susceptibility. 21th International Radiocarbon Conference. Paris, France.
- Reimer, P. J., Baillie, M. G., Bard, E., Bayliss, A., Beck, J. W., Blackwell, P. G., Ramsey, C. B., Buck, C. E., Burr, G. S., Edwards, R. L., Friedrich, M., Grootes, P. M., Guilderson, T. P., Hajdas, I., Heaton, T. J., Hogg, A. G., Hughen, K. A., Kaiser, K. F., Kromer, B., , McCormac, F. G., et al. (2004. INTCAL09 AND MARINE09 RADIOCARBON AGE CALIBRATION CURVES, 0-50,000 YEARS CAL BP(pp 1111-1150).More infoThe IntCal04 and Marine04 radiocarbon calibration curves have been updated from 12 cal kBP (cal kBP is here defined as thousands of calibrated years before AD 1950), and extended to 50 cal kBP, utilizing newly available data sets that meet the IntCal Working Group criteria for pristine corals and other carbonates and for quantification of uncertainty in both the (14)C and calendar timescales as established in 2002. No change was made to the curves from 0-12 cal kBP. The curves were constructed using a Markov chain Monte Carlo (MCMC) implementation of the random walk model used for IntCal04 and Marine04. The new curves were ratified at the 20th International Radiocarbon Conference in June 2009 and; ire available in the Supplemental Material at www.radiocarbon.org.
- Shanahan, T. M., Overpeck, J. T., Scholz, C. A., Beck, J. W., Peck, J., & King, J. W. (1997. Abrupt changes in the water balance of tropical West Africa during the late Quaternary.More info Understanding the causes of tropical climate variability requires an understanding of not only the temporal patterns of these changes, but their spatial extent and magnitude. In this study, we employ a water balance modeling approach to simulate the magnitude of hydrologic changes associated with the geologic record of past lake stands at Lake Bosumtwi, West Africa. Our results indicate that lake level lowering during the late glacial (16 ka) was likely the result of a similar to 20% decrease in precipitation, consistent with general circulation modeling (GCM) results and existing paleohydrological estimates in Africa. In contrast, our observation-based estimate of hydrologic change during the early Holocene (similar to 5-10 ka) is at odds with the magnitude and direction of hydrologic changes predicted by GCM results, suggesting that the models may not adequately reproduce the processes associated with large-scale changes in the West African monsoon. Our results for drought events at 12 and 8.7 ka are also inconsistent with GCM predictions of a precipitation dipole over West Africa, but depend strongly on assumptions about other hydrologic parameters such as relative humidity and temperature. Our water balance model also indicates that significant hydrologic changes occurred in response to changes in orbital forcing at similar to 70-80 ka, possibly associated with an eccentricity-driven shift in precession. Drought conditions also occurred during the same time as the European "Little Ice Age,'' indicating a connection between relatively minor Northern Hemisphere cooling and drought conditions in Africa. These results suggest that the West African monsoon has the potential to respond in a highly nonlinear way to forcing involving changes in the solar radiation over Africa.
- Reimer, P., Baillie, M., McCormac, G., Reimer, R., Bard, E., Beck, J., Blackwell, P., Buck, C., Burr, G., Edwards, R., Friedrich, M., Guilderson, T., Manning, S., Guilderson, T., Southon, ., Hogg, A., Stuiver, M., Hughen, K., van der Plicht, J., , Kromer, B., et al. (2012, APR). Comment on "Radiocarbon calibration curve spanning 0 to 50,000 years BP based on paired Th-230/U-234/U-238 and C-14 dates on pristine corals" by R.G. Fairbanks et al. (Quaternary Science Reviews 24 (2005) 1781-1796) and "Extending the radiocarbon calibration beyond 26,000 years before present using fossil corals" by T.-C. Chin et al. (Quaternary Science Reviews 24 (2005) 1797-1808). QUATERNARY SCIENCE REVIEWS.
- Burr, G. S., Donahue, D. J., Tang, Y., Beck, J. W., McHargue, L., Biddulph, D., Cruz, R., & Jull, A. J. (2007, SEP 1). Error analysis at the NSF-Arizona AMS Facility (vol 259, pg 149, 2007). NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS.
- BECK, J. (2004, MAY 13). SEA-SURFACE TEMPERATURE FROM CORAL SKELETAL STRONTIUM CALCIUM RATIOS (VOL 257, PG 644, 1992). SCIENCE.
- Jull, A., Beck, J., Burr, G., Gilmour, I., Sephton, M., & Pillinger, C. (2004, JUL). Isotopic evidence for abiotic organic compounds in the martian meteorite nakhla.. METEORITICS & PLANETARY SCIENCE.