HR: 15:00h
AN: PP52B-06 INVITED     [PDF]
TI: Coccolith Chemistry as a Paleoceanographic Indicator in Paleogene and Neogene Sediments
AU: * Stoll, H M
EM: hstoll@williams.edu
AF: Geoscience Dept. Williams College, 947 Main St, Williamstown, MA 01267 United States
AB: Coccoliths are the dominant form of carbonate in many Neogene and Paleogene marine sediments. Recent culture and sediment core top studies suggest that coccolith Sr/Ca ratios increase with nutrient-stimulated growth rates, potentially offering a new indicator of the productivity of the coccolithophorid algae. Unlike many other common productivity indicators, the coccolith Sr/Ca indicator does not depend on knowledge of the sediment accumulation rate which can be difficult to determine with precision in pre-Quaternary sediments. Separation of near-monospecific coccolith fractions from sediments can yield species-specific Sr/Ca records. This method was applied to sediments from the Weddell Sea (ODP site 690) to test whether marine productivity increased during the Paleocene-Eocene Thermal Maximum. In the dominant coccolithophorid genus Toweius, a large (40%) Sr/Ca increase immediately after the carbon isotope excursion suggests an important increase in nutrient availability and coccolithophorid productivity. Productivity levels remain high for 60,000 years but decrease to pre-event levels within 120,000 years. Elevated productivity corresponds with locally and globally increased silicate weathering intensity indicated by published clay mineral assemblages and Os isotope records; increased weathering intensity may have accelerated nutrient fluxes to near-continent regions. If this type of productivity response occurred globally, it would also be consistent with the timing of C drawdown that may have returned temperatures to near pre-event levels. Unfortunately, at other PETM sites like Blake-Bahama Plateau (ODP 1051) and Shatsky Rise (ODP 1209), application of the coccolith Sr/Ca technique is limited by abundant non-coccolith carbonate in the coccolith size fraction. Analysis of stable isotopes in near-monospecific coccolith fractions from Paleocene sediments illustrates a small range of vital effects among different species and reaffirms the fidelity of coccolith-dominated bulk carbonate records for this event.
DE: 1615 Biogeochemical processes (4805)
DE: 3030 Micropaleontology
DE: 4267 Paleoceanography
DE: 4875 Trace elements
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting