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Towards radiocarbon calibration beyond 28 ka using speleothems from the Bahamas
Authors:Dirk L Hoffmann  J Warren Beck  David A Richards  Peter L Smart  Joy S Singarayer  Tricia Ketchmark  Chris J Hawkesworth
Institution:1. BioArCh, Department of Archaeology, University of York, Environment Building, Wentworth Way, York, YO10 5DD, UK.;2. Marine Science Laboratory, Universidade do Sul de Santa Catarina (UNISUL), Av J. Acácio Moreira, 787, Dehon, Tubarão 88704-900, Brazil.;3. Museu de Arqueologia e Etnologia, Universidade de São Paulo (USP), Av. Prof. Almeida Prado, 1466, Butantã, São Paulo 05508-070, Brazil.;4. Department of Physics, University of York, Heslington, York YO10 5DD, UK.;5. York Centre for Complex Systems Analysis, University of York, York YO10 5GE, UK.;6. Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, P.O. Box 1527, GR-711 10 Heraklion, Greece.;7. Grupep, Universidade do Sul de Santa Catarina (UNISUL), Av J. Acácio Moreira, 787, Dehon, Tubarão 88704-900, Brazil.;8. Institute of Geosciences, University of Mainz, J.-J.-Becher-Weg 21, 55128 Mainz, Germany.;9. Instituto de Geociências, Universidade de São Paulo (USP), R. do Lago, 562, Cidade Universitária, São Paulo 05508-080, Brazil.;1. Ruhr University Bochum, Institute for Geology, Mineralogy and Geophysics, Universitätsstrasse 150, 44801 Bochum, Germany;2. Johannes Gutenberg University Mainz, Institute for Geosciences, Johann Joachim Becher-Weg 21, 55128 Mainz, Germany
Abstract:We present a new speleothem record of atmospheric Δ14C 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 14C ages, using new low-blank protocols, and U–Th ages using high precision MC-ICPMS procedures. Atmospheric Δ14C was calculated by correcting 14C ages with a constant dead carbon fraction (DCF) of 22.7 ± 5.9%, based on a comparison of stalagmite 14C ages with the IntCal04 (Reimer et al., 2004) calibration curve between 15 and 11 ka. The new Δ14C 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 14C data set for a stalagmite record from the Bahamas — GB-89-24-1 (Beck et al., 2001), which likely suffered from 14C analytical blank subtraction issues in the older part of the record. The new Bahamas speleothem ?14C 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 Δ14C 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 ?14C 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.
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