HR: 14:40h
AN: PP43E-05 INVITED    [Abstracts]
TI: First observational evidence for long-term CO2-driven weathering feedback
AU: * Zeebe, R E
EM: zeebe@hawaii.edu
AF: School of Ocean and Earth Science and Technology, Department of Oceanography, University of Hawaii at Manoa, 1000 Pope Road, MSB 504, Honolulu, HI 96822, United States
AU: Caldeira, K
EM: kcaldeira@globalecology.stanford.edu
AF: Department of Global Ecology, Carnegie Institution, 260 Panama Street, Stanford, CA 94305, United States
AB: Feedbacks controlling long-term carbon cycle fluxes and atmospheric CO₂ are critical in stabilizing Earth's long-term climate. CO₂ levels over millions of years are controlled by a CO₂-driven weathering feedback that maintains a mass balance between CO₂ input to the atmosphere from volcanism/metamorphism and net organic carbon oxidation, and CO₂ removal from the atmosphere by silicate-rock weathering and subsequent burial of carbonate minerals. This view is frequently challenged by hypotheses avoiding the need for a mass balance and invoking other processes that affect CO₂, including continental uplift and organic carbon burial. Hitherto, the prevailing conjectural argument in support of the mass balance theory was that flux imbalances would lead to untenable variations in atmospheric CO₂ within a few million years. Here we provide the first observational evidence for a close mass balance of long-term carbon cycle fluxes, based on ice core CO₂ data over the late Pleistocene and indicators of carbonate dissolution in the ocean. Our analysis shows that mean global atmospheric CO₂ and Antarctic temperature have changed during the past 610~ky by at most ~\!22~ppmv and 1.5 to 2~K, respectively. Forcing of carbon cycle models with these data allows for a maximum imbalance of ca.\ 1-2% between CO₂ supply and CO₂ uptake by silicate weathering over 610~ky. This presupposes that only changes in long-term processes caused the average CO₂ change - otherwise, even finer balances are possible. This shows that a tight balance exists between CO₂ inputs to the atmosphere and continental weathering uptake on the time scale of several hundred thousand years, despite climate variations on shorter timescales. Our results provide strong support for a CO₂-driven weathering feedback.
DE: 1039 Alteration and weathering processes (3617)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4806 Carbon cycling (0428)
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4932 Ice cores (0724)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting