HR: 1340h
AN: PP13A-0582    [Abstracts]
TI: Using high-resolution radiocarbon and trace-element variation in speleothems to investigate the climate-system during the last deglaciation
AU: * Richards, D A
EM: david.richards@bristol.ac.uk
AF: School of Geographical Sciences, University of Bristol , Bristol, BS8 1SS United Kingdom
AU: Hoffmann, D L
AF: School of Geographical Sciences, University of Bristol , Bristol, BS8 1SS United Kingdom
AU: Beck, W
AF: NSF Accelerator Mass Spectrometry Facility, Department of Physics, University of Arizona, Tucson, AZ 85721 United States
AU: Smart, P L
AF: School of Geographical Sciences, University of Bristol , Bristol, BS8 1SS United Kingdom
AU: Hopley, P J
AF: School of Geographical Sciences, University of Bristol , Bristol, BS8 1SS United Kingdom
AU: Paterson, B A
AF: Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ United Kingdom
AU: Hawkesworth, C J
AF: Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ United Kingdom
AU: Mattey, D P
AF: Department of Geology, Royal Holloway, University of London, Surrey, TW20 0EX United Kingdom
AB: Significant fluctuations in the atmospheric concentration of radiocarbon ($\Delta$$^{14}$C) have been observed at decadal to millennial timescales and attributed to changes in terrestrial or solar magnetic fields, and/or changes in the carbon cycle, particularly ocean circulation. Previously, we presented a continuous record of atmospheric radiocarbon ($^{14}$C) from 45 to 11 ka based on TIMS U, Th and Pa measurements and AMS $^{14}$C ages of a stalagmite (GB-89-24-1) from a cave on Grand Bahama (Beck {\it et al}, 2001). This record revealed elevated $\Delta$$^{14}$C for the duration of growth and a general decline in $\Delta$$^{14}$C between 26 and 11 ka, from $\sim$ 700 to $\sim$ 100 $\permil$, which was considered too large to be solely a result of reduced production via increased shielding by the Earth's magnetic field and was probably related to redistribution of $^{14}$ during a mode of ocean circulation much different to the present day. Here, we focus on efforts to reproduce and explain the millennial and sub-millennial variations that are superimposed on the general decreasing trend from 26 to 11 ka. We present $>$200 new AMS $^{14}$C ages from additional Bahamas samples that confirm the millennial-scale fluctuations of $\Delta$$^{14}$C $>$ 100 $\permil$ during the last deglaciation recorded in the stalagmite GB-89-24-1. Robust chronologies for the additional stalagmites have been obtained using MC-ICPMS U and Th isotope measurements with precisions comparable to AMS 14C measurements for similar sample sizes. Comparison of high-resolution laser-ablation trace-element profiles between different samples has significantly improved our ability to constrain age models and, at the same time, provide climate information. The profiles of $\delta$$^{18}$O, $\delta$$^{13}$C, Sr, Mg, Ba and U variations are likely to be indicative of the changing climate and/or recharge. Changes in $^{14}$C coincide with abrupt shifts in climate as recorded in the Greenland ice cores ($\delta$$^{18}$O) for the last glacial period and deglaciation. We explore the implications of the speleothem $^{14}$C record by comparison with records of $^{231}$Pa/$^{230}$Th, Cd/Ca, $\delta$$^{13}$C and SST from various high-resolution cores from the North Atlantic for last deglaciation. During the last deglaciation, rapid reduction in $\Delta$$^{14}$C occurred at times of inferred warming in Greenland, increases in North Atlantic Deep Water (NADW) formation and abrupt shifts in sea surface temperatures in the Atlantic. One of the most dramatic shifts occurs at $\sim$ 14.5 ka and is correlated with the Bolling transition. We also suggest that atmospheric $\Delta$$^{14}$C levels were enhanced during periods of reduced thermohaline circulation related to Heinrich events 1, 2 and the Younger Dryas.
UR: http://www.ggy.bris.ac.uk/research/karst/radiocarbon.htm
DE: 4267 Paleoceanography
DE: 3309 Climatology (1620)
DE: 1035 Geochronology
DE: 1040 Isotopic composition/chemistry
DE: 0330 Geochemical cycles
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting