HR: 0800h
AN: PP11B-0558    [Abstracts]
TI: Decoupled Shelf-Ocean Phytoplankton Productivity Responses Across the Paleocene-Eocene Thermal Maximum
AU: * Gibbs, S J
EM: sgibbs@geosc.psu.edu
AF: Department of Geosciences, Pennsylvania State University, University Park, PA 16802 United States
AU: Bralower, T J
EM: bralower@geosc.psu.edu
AF: Department of Geosciences, Pennsylvania State University, University Park, PA 16802 United States
AU: Boharty, S
EM: sbohaty@es.ucsc.edu
AF: Earth Science Department, University of California, Santa Cruz, CA 95064 United States
AU: Zachos, J
EM: jzachos@es.ucsc.edu
AF: Earth Science Department, University of California, Santa Cruz, CA 95064 United States
AU: Bybell, L M
EM: lbybell@usgs.gov
AF: U.S. Geological Survey, 926 National Center, Reston, VA 20192 United States
AU: Quattlebaum, T
EM: thomasqtl@yahoo.com
AF: Earth Science Department, University of California, Santa Cruz, CA 95064 United States
AB: Significant transformations in the global biosphere accompanied dramatic global warming and profound perturbation of the carbon cycle during the Paleocene Eocene Thermal Maximum (PETM, $\sim$55 Ma). These abrupt changes have been linked to a massive release of light carbon into the ocean-atmosphere system. Increased phytoplankton productivity has been cited as a mechanism responsible for subsequent CO$_{2}$ draw-down. However, interpretations of geochemical and biotic data differ on where this increased productivity occurred. Here we constrain the loci of increased productivity using highly detailed nannofossil assemblage data. Calcareous nannofossils provide an excellent basis to monitor changes in primary production during the PETM given their sensitivity to surface water conditions, especially availability of nutrients. We present nannofossil assemblage records from productivity end-member environments: a central gyre setting (ODP Site 1209, Shatsky Rise, paleo-equatorial Pacific), a high-latitude, open-ocean setting (ODP Site 738, Indian Ocean sector of the Southern Ocean) and a neritic setting (USGS Wilson Lake drill hole, New Jersey). Nannofossil assemblages at all three sites display a pattern of continuous reorganization during the PETM. In particular, assemblage shifts at Shatsky Rise demonstrate a short-lived interval of extremely low productivity coincident with the carbon isotope excursion. In contrast, assemblages at Wilson Lake suggest a transient shift to more mesotrophic conditions. Combined with published planktonic assemblage records, these data produce a global picture of productivity change across the PETM with shelf areas and the open ocean clearly decoupled regardless of latitude. Open ocean sites demonstrate a global but transient increase in oligotrophy which may have resulted from a widespread deepening of the thermocline. Shelf productivity increase is localized with mesotrophic communities spatially restricted to areas close to nutrient sources via increased precipitation and runoff.
DE: 9604 Cenozoic
DE: 4805 Biogeochemical cycles (1615)
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 3030 Micropaleontology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting