Guilderson
Thomas P.
Guilderson
Thomas P.
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ArticleMarine04 marine radiocarbon age calibration, 0-26 cal kyr BP(Dept. of Geosciences, University of Arizona, 2004) Hughen, Konrad A. ; Baillie, Mike G. L. ; Bard, Edouard ; Beck, J. Warren ; Bertrand, Chanda J. H. ; Blackwell, Paul G. ; Buck, Caitlin E. ; Burr, George S. ; Cutler, Kirsten B. ; Damon, Paul E. ; Edwards, R. Lawrence ; Fairbanks, Richard G. ; Friedrich, Michael ; Guilderson, Thomas P. ; Kromer, Bernd ; McCormac, Gerry ; Manning, Sturt ; Bronk Ramsey, Christopher ; Reimer, Paula J. ; Reimer, Ron W. ; Remmele, Sabine ; Southon, John R. ; Stuiver, Minze ; Talamo, Sahra ; Taylor, F. W. ; van der Plicht, Johannes ; Weyhenmeyer, Constanze E.New 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 cal kyr BP. 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 14C reservoir age information to provide a single global marine mixed-layer calibration from 10.5–26.0 cal kyr BP. 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 14C 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).
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ArticleBioturbation artifacts in zero-age sediments(American Geophysical Union, 2009-12-15) Keigwin, Lloyd D. ; Guilderson, Thomas P.Most seafloor sediments are dated with radiocarbon, and the sediment is assumed to be zero-age (modern) when the signal of atmospheric testing of nuclear weapons is present (Fraction modern (Fm) > 1). Using a simple mass balance, we show that even with Fm > 1, half of the planktonic foraminifera at the seafloor can be centuries old, because of bioturbation. This calculation, and data from four core sites in the western North Atlantic indicate that, first, during some part of the Little Ice Age (LIA) there may have been more Antarctic Bottom Water than today in the deep western North Atlantic. Alternatively, bioturbation may have introduced much older benthic foraminifera into surface sediments. Second, paleo-based warming of Sargasso Sea surface waters since the LIA must lag the actual warming because of bioturbation of older and colder foraminifera.
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ArticleReproducibility of Ba/Ca variations recorded by northeast Pacific bamboo corals(John Wiley & Sons, 2017-09-13) Serrato Marks, Gabriela ; LaVigne, Michèle ; Hill, Tessa M. ; Sauthoff, Wilson ; Guilderson, Thomas P. ; Roark, E. Brendan ; Dunbar, Robert B. ; Horner, Tristan J.Trace elemental ratios preserved in the calcitic skeleton of bamboo corals have been shown to serve as archives of past ocean conditions. The concentration of dissolved barium (BaSW), a bioactive nutrientlike element, is linked to biogeochemical processes such as the cycling and export of nutrients. Recent work has calibrated bamboo coral Ba/Ca, a new BaSW proxy, using corals spanning the oxygen minimum zone beneath the California Current System. However, it was previously unclear whether Ba/Cacoral records were internally reproducible. Here we investigate the accuracy of using laser ablation inductively coupled plasma mass spectrometry for Ba/Cacoral analyses and test the internal reproducibility of Ba/Ca among replicate radial transects in the calcite of nine bamboo corals collected from the Gulf of Alaska (643–720 m) and the California margin (870–2054 m). Data from replicate Ba/Ca transects were aligned using visible growth bands to account for nonconcentric growth; smoothed data were reproducible within ~4% for eight corals (n = 3 radii/coral). This intracoral reproducibility further validates using bamboo coral Ba/Ca for BaSW reconstructions. Sections of the Ba/Ca records that were potentially influenced by noncarbonate bound Ba phases occurred in regions where elevated Mg/Ca or Pb/Ca and coincided with anomalous regions on photomicrographs. After removing these regions of the records, increased Ba/Cacoral variability was evident in corals between ~800 and 1500 m. These findings support additional proxy validation to understand BaSW variability on interannual timescales, which could lead to new insights into deep sea biogeochemistry over the past several centuries.
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ArticleThe 129-iodine content of subtropical Pacific waters : impact of Fukushima and other anthropogenic 129-iodine sources(Copernicus Publications on behalf of the European Geosciences Union, 2014-09-11) Guilderson, Thomas P. ; Tumey, S. J. ; Brown, T. A. ; Buesseler, Ken O.Results obtained from a dedicated radiochemistry cruise approximately 100 days after the 11 March 2011 Tohoku earthquake and subsequent disaster at the Fukushima Daiichi Nuclear Power Plant show that Fukushima derived radionuclides in the nearby ocean environment had penetrated, on average, to ≤250 m depth (1026.5 kg m3 potential density surface). The excess inventory of Fukushima-derived 129I in the region (∼150 000 km2) sampled during the cruise is estimated to have been between 0.89 and 1.173 billion Bq (∼136 to ∼179 grams) of 129I. Based on a tight tracer–tracer relation with 134Cs (or 137Cs) and estimates that most of the excess cesium is due to direct discharge, we infer that much of the excess 129I is from direct (non-atmospheric deposition) discharge. After taking into account oceanic transport, we estimate the direct discharge, i.e., that directly released into the ocean, off Fukushima to have been ∼1 kg 129I. Although this small pulse is dwarfed by the ~90 kg of weapons-testing-derived 129I that was released into the environment in the late 1950s and early 1960s, it should be possible to use Fukushima-derived 129I and other radionuclides (e.g., 134, 137Cs) to study transport and entrainment processes along and across the Kuroshio Current.
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ArticleIntCal09 and Marine09 radiocarbon age calibration curves, 0–50,000 years cal BP(Dept. of Geosciences, University of Arizona, 2009-12) Reimer, Paula J. ; Bard, Edouard ; Bayliss, Alex ; Beck, J. Warren ; Blackwell, Paul G. ; Bronk Ramsey, Christopher ; Buck, Caitlin E. ; Cheng, Hai ; Edwards, R. Lawrence ; Friedrich, Michael ; Grootes, Pieter M. ; Guilderson, Thomas P. ; Haflidason, Haflidi ; Hajdas, Irka ; Hatte, Christine ; Heaton, Timothy J. ; Hoffmann, Dirk L. ; Hogg, Alan G. ; Hughen, Konrad A. ; Kaiser, K. Felix ; Kromer, Bernd ; Manning, Sturt W. ; Niu, Mu ; Reimer, Ron W. ; Richards, David A. ; Scott, E. Marian ; Southon, John R. ; Staff, Richard A. ; Turney, Christian S. M. ; van der Plicht, JohannesThe 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 14C 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 are available in the Supplemental Material at www.radiocarbon.org.
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ArticleThe Intcal20 Northern Hemisphere radiocarbon age calibration curve (0-55 cal kBP)(Cambridge University Press, 2020-08-12) Reimer, Paula J. ; Austin, William E. N. ; Bard, Edouard ; Bayliss, Alex ; Blackwell, Paul G. ; Bronk Ramsey, Christopher ; Butzin, Martin ; Cheng, Hai ; Edwards, R. Lawrence ; Friedrich, Michael ; Grootes, Pieter M. ; Guilderson, Thomas P. ; Hajdas, Irka ; Heaton, Timothy J. ; Hogg, Alan G. ; Hughen, Konrad A. ; Kromer, Bernd ; Manning, Sturt W. ; Muscheler, Raimund ; Palmer, Jonathan G. ; Pearson, Charlotte ; van der Plicht, Johannes ; Reimer, Ron W. ; Richards, David A. ; Scott, E. Marian ; Southon, John R. ; Turney, Christian S. M. ; Wacker, Lukas ; Adolphi, Florian ; Büntgen, Ulf ; Capano, Manuela ; Fahrni, Simon M. ; Fogtmann-Schulz, Alexandra ; Friedrich, Ronny ; Köhler, Peter ; Kudsk, Sabrina ; Miyake, Fusa ; Olsen, Jesper ; Reinig, Frederick ; Sakamoto, Minoru ; Sookdeo, Adam ; Talamo, SahraRadiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.
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ArticleNotCal04; comparison/ calibration 14C records 26-50 cal kyr BP(Dept. of Geosciences, University of Arizona, 2004) van der Plicht, Johannes ; Beck, J. Warren ; Bard, Edouard ; Baillie, Mike G. L. ; Blackwell, Paul G. ; Buck, Caitlin E. ; Friedrich, Michael ; Guilderson, Thomas P. ; Hughen, Konrad A. ; Kromer, Bernd ; McCormac, F. G. ; Bronk Ramsey, Christopher ; Reimer, Paul J. ; Reimer, Ron W. ; Remmele, Sabine ; Richards, D. A. ; Southon, John R. ; Stuiver, Minze ; Weyhenmeyer, Constanze E.The radiocarbon calibration curve IntCal04 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.
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ArticleGlobal ocean radiocarbon programs(Cambridge University Press, 2022-04-21) McNichol, Ann P. ; Key, Robert M. ; Guilderson, Thomas P.The importance of studying the radiocarbon content of dissolved inorganic carbon (DI14C) in the oceans has been recognized for decades. Starting with the GEOSECS program in the 1970s, 14C sampling has been a part of most global survey programs. Early results were used to study air-sea gas exchange while the more recent results are critical for helping calibrate ocean general circulation models used to study the effects of climate change. Here we summarize the major programs and discuss some of the important insights the results are starting to provide.
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ArticleIntCal04 terrestrial radiocarbon age calibration, 0-26 cal kyr BP(Dept. of Geosciences, University of Arizona, 2004) Reimer, Paula J. ; Baillie, Mike G. L. ; Bard, Edouard ; Bayliss, Alex ; Beck, J. Warren ; Bertrand, Chanda J. H. ; Blackwell, Paul G. ; Buck, Caitlin E. ; Burr, George S. ; Cutler, Kirsten B. ; Damon, Paul E. ; Edwards, R. Lawrence ; Fairbanks, Richard G. ; Friedrich, Michael ; Guilderson, Thomas P. ; Hogg, Alan G. ; Hughen, Konrad A. ; Kromer, Bernd ; McCormac, Gerry ; Manning, Sturt ; Bronk Ramsey, Christopher ; Reimer, Ron W. ; Remmele, Sabine ; Southon, John R. ; Stuiver, Minze ; Talamo, Sahra ; Taylor, F. W. ; van der Plicht, Johannes ; Weyhenmeyer, Constanze E.A new calibration curve for the conversion of radiocarbon ages to calibrated (cal) ages has been constructed and internationally ratified to replace IntCal98, 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 IntCal98. 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 IntCal98 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 14C 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 (Marine04) 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).