Carbon Cycle Variations during the Last Glacial Period Based on Atmospheric Delta 14C

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AbstractWe have recently generated a long record of atmospheric between 11-45 ka BP using coupled AMS 14C and TIMS U/Th and U/Pa dating of a stalagmite recovered from a cave in the Bahamas (Beck et al.,2001;Richards et al., in Press).This record reveals highly elevated 14 C during the last glacial period, especially between 45 and 33 ka BP.Superimposed on this broad peak of 14 C are numerous rapid excursions, the largest of which occurs between 44.3 and 43.3 ka. While some of the structure revealed in this record is clearly linked to variations in the terrestrial magnetic field, other structures appear to be correlated with Dansgaard/Oeschger variations revealed in the GISP2 18O record, or linked to Heinrich events H1-H5.Carbon cycle box models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone, but also require significant fluctuations in the global carbon cycle as well. In this proposal, we plan to validate this existing atmospheric 14 C record by generating additional speleothem D14C records, and to further explore the causes of the observed fluctuations using carbon cycle box models using appropriate inputs from sedimentary Cd/Ca,Ba/Ca,, C, 15N and ice core 18 O to constrain ocean ventilation rates and biological pump variability. Existing ice core records of 36Cl and 10Be will be used in conjunction with the SINT-200 and NAPIS-75 paleomagnetic records, and with new stalagmite 10 Be and 129 I records to constrain 14 C fluctuations stemming from solar and magnetic forcing. A particular focus of these efforts will be evaluation of climate induced changes in the carbon cycle that may have accompanied Heinrich events H1,H2,H3, H4 and H5 and Dansgaard/Oeschger cycles 1-12. Among the broader impacts of this proposed work is a better understanding of the potential linkages between climate and the carbon cycle for conditions of enhanced freshwater flux to the polar oceans.This work will be conducted in collaboration with researchers at the University of Bristol, England, and Royal Holloway, University of London, England. This collaborative effort will utilize stalagmites already in the Bristol collection and identified as good candidates in the appropriate age range for this exercise. Separate funding for the UK portion of this research for generation of TIMS U/Th chronology, stable isotope records, and part of the modeling effort has already been procured through grants from NERC and the Leverhulme Trust foundation (see letter of support). Stalagmite 18O records will also be generated as part of the UK effort, to be used for correlating 14 C fluctuations with GISP2 climate records (Wang et al.,2001; Dorale et al.,1998). Funds are requested in this proposal to only support the AMS 14 C measurement component of this effort, and to support the University of Arizona component of the coupled carbon cycle modeling effort.