HR: 16:00h
AN: PP14A-01    [Abstracts]
TI: Model Simulations of the Global Carbon and Sulfur Cycles: Implications for the Paleocene-Eocene Thermal Maximum
AU: * Higgins, J A
EM: jhiggins@fas.harvard.edu
AF: Harvard University, 20 Oxford St., Cambridge, MA 02138 United States
AU: Schrag, D P
EM: schrag@eps.harvard.edu
AF: Harvard University, 20 Oxford St., Cambridge, MA 02138 United States
AB: Extreme global warmth and an abrupt negative carbon isotope excursion during the Paleocene-Eocene Thermal Maximum (PETM) have been attributed to a rapid addition of isotopically depleted carbon to the ocean-atmosphere system. Potential carbon sources include the abrupt release of 1000-2000 Gt C as methane hydrate (\delta$^{13}$C ~-60\permil) from sediments on the continental slope (Dickens et al., 1995) and the oxidation of 8000-9000 Gt of organic carbon (\delta$^{13}$C ~-25\permil) in rampant global wildfires (Kurtz et al., 2003). Using a simple geochemical model of the global carbon and sulfur cycles, we investigate whether these hypotheses are consistent with estimates of climate warming during the PETM by considering the effects of atmospheric composition and climate in the Paleocene and feedbacks driven by changes in sulfur cycling and seawater chemistry. Modest increases in atmospheric CO$_{2}$ (70-150 ppm) associated with methane hydrate release cannot, without additional feedbacks in the climate system, account for a $5-6\deg$ C increase in global sea surface temperature during the PETM. In contrast, a significant increase in atmospheric CO$_{2}$ (600-700 ppm) is observed following the oxidation of 8000-9000 Gt of organic carbon. However, constraints on the size and extent of the Paleocene terrestrial carbon pool and the absence of geologic evidence indicative of vast wildfires argue against a global conflagration as an important source of depleted carbon. Instead, we interpret the PETM and its associated negative carbon isotope excursion as representing the oxidation of 8000-9000 Gt C as organic matter in shallow marine and near shore terrestrial sediments following the retreat of major epicontinental seaways in the Paleocene. This hypothesis is also consistent with large changes in the sulfur cycle in the early Eocene inferred from the \delta$^{34}$S of seawater sulfate. References: Dickens G.R., et al., (1995) Paleoceanography, 10, 965-971. Kurtz, A.C., et al., (2003) Paleoceanography, 18, 1090-1104.
DE: 4835 Inorganic marine chemistry
DE: 3344 Paleoclimatology
DE: 1615 Biogeochemical processes (4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting