HR: 0800h
AN: PP11A-0551    [Abstracts]
TI: The Carbon and Sulfur Cycles through the Cenozoic: Insight from Oxygen Isotopes in Marine Sulfate
AU: * Turchyn, A V
EM: avan@fas.harvard.edu
AF: Harvard University, Department of Earth and Planetary Sciences 20 Oxford St, Cambridge, MA 02138 United States
AU: Schrag, D P
EM: schrag@eps.harvard.edu
AF: Harvard University, Department of Earth and Planetary Sciences 20 Oxford St, Cambridge, MA 02138 United States
AB: Marine sulfate plays an important role in the cycling of biochemicals in organic rich sediments, serving as the terminal electron acceptor in the remineralization of organic matter and responsible for nearly all anaerobic methane oxidation. Because sulfur isotopes are largely conserved during sulfur cycling in organic rich sediments, they reflect mostly changes in net sulfur burial, and have been used to study fluctuations in sulfur mineral burial over Earth history. Recently, we have shown that temporal variability in oxygen isotopes measured in marine sulfate (d18O-SO4) highlight changes the pathways of sulfur cycling on continental margins because the d18O-SO4 is reset during sulfate reduction and sulfide reoxidation. The fluxes associated with sulfur cycling, predominantly in shallow sediments, are nearly three times larger than riverine input. We present a continuous record of d18O-SO4 in marine barite over the Cenozoic. There is considerable variability in the d18OSO4, with major peaks 55, 15, and 3 million years ago. There is little correlation between sulfur isotopes in marine sulfate and d18O-SO4, illustrating the fact that different processes control the sulfur and oxygen isotopic composition of sulfate. The peaks in the d18O-SO4 at 55 and 15 Ma coincide with peaks in the d13C of benthic foraminifera, highlighting the connection between the carbon and sulfur cycles in organic rich sediments. In addition, the increase in the d18O of the ocean (measured in benthic foraminifera) between 34 and 28 Ma coincides with a slight increase in the d18O-SO4. We have modeled the sulfur cycle for both sulfur and oxygen isotopes and will show model results and interpretation over several key intervals over the Cenozoic, including the Mid-Miocene Climate Optimum, the Eocene-Oligocene boundary, and the Paleocene productivity high.
DE: 4805 Biogeochemical cycles (1615)
DE: 4870 Stable isotopes
DE: 4267 Paleoceanography
DE: 1045 Low-temperature geochemistry
DE: 1050 Marine geochemistry (4835, 4850)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting