HR: 14:45h
AN: PP53D-05    [Abstracts]
TI: Effects of Organic Carbon/Carbonate Burial Ratios and Biological Carbon Fixation on the Global Carbon Cycle Over the Past ~200 myr
AU: * Katz, M E
EM: mimikatz@rci.rutgers.edu
AF: Dept. of Geological Sci., 610 Taylor Rd. Rutgers Univ., Piscataway, NJ 08854 United States
AU: Milligan, A J
EM: allenm@imcs.rutgers.edu
AF: Inst. of Marine & Coastal Sci., 71 Dudley Road Rutgers Univ., New Brunswick, NJ 08901 United States
AU: Cramer, B S
EM: benjamin@dges.tohoku.ac.jp
AF: Inst. of Geology and Paleontology, Tohoku University Aoba, Aramaki, Sendai, 980-8578 Japan
AU: Fennel, K
EM: kfennel@imcs.rutgers.edu
AF: Inst. of Marine & Coastal Sci., 71 Dudley Road Rutgers Univ., New Brunswick, NJ 08901 United States
AU: Miller, K G
EM: kgm@rci.rutgers.edu
AF: Dept. of Geological Sci., 610 Taylor Rd. Rutgers Univ., Piscataway, NJ 08854 United States
AU: Wright, J D
EM: jdwright@rci.rutgers.edu
AF: Dept. of Geological Sci., 610 Taylor Rd. Rutgers Univ., Piscataway, NJ 08854 United States
AU: Falkowski, P G
EM: falko@imcs.rutgers.edu
AF: Dept. of Geological Sci., 610 Taylor Rd. Rutgers Univ., Piscataway, NJ 08854 United States
AU: Falkowski, P G
EM: falko@imcs.rutgers.edu
AF: Inst. of Marine & Coastal Sci., 71 Dudley Road Rutgers Univ., New Brunswick, NJ 08901 United States
AB: The isotopic composition of the global carbon reservoir integrates large kinetic fractionations from photosynthesis with small thermodynamic fractionations from carbonate precipitation. We present concordant $\delta$$^{13}$C records of carbonates ($\delta$$^{13}$C$_{carb}$) and organic matter ($\delta$$^{13}$C$_{org}$), along with new carbonate (C$_{carb}$) and organic carbonate (C$_{org}$) fluxes for the past $\sim$205 myrs (Jurassic-Cenozoic) generated from bulk sediment samples from the Atlantic. The new $\delta$$^{13}$C$_{org}$ record greatly refines previous compilations (Hayes et al., 1999) by providing a sample resolution of $\sim$100-300 kyrs. Model simulations using these $\delta$$^{13}$C$_{carb}$ and $\delta$$^{13}$C$_{org}$ data provide constraints on carbon sources (mantle and weathering) and sinks (carbonate and organic carbon sedimentation); comparisons with the flux records provide insight on the components of the geological carbon cycle. Stable isotope records indicate that long-term net depletion of $^{12}$C from mobile carbon reservoirs was a consequence of an organic carbon burial fraction increase of $\sim$0.05-0.1 that began in the Jurassic ($\sim$200 Ma). Superimposed on the long-term trend are higher-order variations (5-10s of myrs) in $\delta$$^{13}$C$_{carb}$ and $\delta$$^{13}$C$_{org}$ that show episodic intervals of elevated values. In contrast to paleoceanographic convention, organic carbon burial is often decoupled from global $\delta$13C variations on the 5-10s of myrs scale. Brief episodes of elevated C$_{org}$ flux tend to occur near the onset and cessation of these intervals of elevated $\delta$$^{13}$C$_{carb}$ and $\delta$$^{13}$C$_{org}$ values; prolonged episodes of elevated C$_{carb}$ flux tend to correspond to the cessation of extended intervals of elevated $\delta$$^{13}$C values. In the latter part of the Cenozoic, the development of $\beta$ carboxylation and C$_{4}$ photosynthetic pathways in phytoplankton and terrestrial plants increasingly influenced $\delta$$^{13}$C$_{org}$, ultimately contributing to the reversal of the long-term trend in $\delta$$^{13}$C$_{carb}$. Thus, the geologic record of the global carbon cycle over the past 205 myr has been influenced by a combination of changes in carbonate burial, organic carbon burial, and biological fixation.
DE: 4835 Inorganic marine chemistry
DE: 4850 Organic marine chemistry
DE: 4870 Stable isotopes
DE: 4267 Paleoceanography
DE: 0400 Biogeosciences
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting