HR: 0800h
AN: PP31A-0182    [Abstracts]
TI: Anthropogenic CO₂ in the North Atlantic Subtropical Gyre: Estimates based on benthic foraminiferal δ¹³C
AU: * Lund, D C
EM: dlund@gps.caltech.edu
AF: California Institute of Technology, MS 100-23, Pasadena, CA 91125, United States
AB: The fate of anthropogenic CO₂ in the ocean-atmosphere system is of critical importance to predictions of future climate change. Modern dissolved inorganic carbon data have been used to quantify anthropogenic inputs of CO₂ into the ocean, but this approach is based on a set of complex assumptions and it lacks the time perspective provided by the marine geologic record. We will present evidence for the ¹³C Suess effect in the North Atlantic subtropical gyre based on benthic foraminiferal ( Cibicidoides floridanus) carbon stable isotope data from the Great Bahama Bank. Four separate time series from water depths 260, 440, 530, and 700 meters show depletions in ¹³C over the past 200 years. In each case, the depletion is anomalous in the context of the last millennium. The δ¹³C anomaly decreases as water depth increases, consistent with an atmospheric source. Comparison with a foraminiferal δ¹³C record from 46°N suggests the δ¹³C anomaly enters the upper ocean in the isopycnal outcropping region of the North Atlantic and is transported southward to the Great Bahama Bank. Using simple mass balance calculations, we estimate there is approximately 20 to 40 μmol/kg of anthropogenic CO₂ at intermediate depths of the subtropical gyre, consistent with estimates based on modern oceanographic data. These results imply that high-resolution, well- dated benthic foraminiferal stable isotope records have the potential to be used as an independent means for constraining the oceanic sink of anthropogenic carbon dioxide.
DE: 1635 Oceans (1616, 3305, 4215, 4513)
DE: 4806 Carbon cycling (0428)
DE: 4902 Anthropogenic effects (1803, 4802)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting