HR: 11:35h
AN: PP32A-06    [Abstracts]
TI: Testing the Silicic Acid Leakage Hypothesis: A Paleoproductivity Reconstruction in the Eastern Equatorial Pacific From the Last Glacial Maximum to the Present
AU: * Bradtmiller, L I
EM: louisab@ldeo.columbia.edu
AF: The Lamont-Doherty Earth Observatory of Columbia University, 61 Rte. 9W, Palisades, NY 10964 United States
AU: * Bradtmiller, L I
EM: louisab@ldeo.columbia.edu
AF: Department of Earth and Environmental Science, Columbia University, 2960 Broadway, New York, NY 10027 United States
AU: Anderson, R F
EM: boba@ldeo.columbia.edu
AF: The Lamont-Doherty Earth Observatory of Columbia University, 61 Rte. 9W, Palisades, NY 10964 United States
AU: Anderson, R F
EM: boba@ldeo.columbia.edu
AF: Department of Earth and Environmental Science, Columbia University, 2960 Broadway, New York, NY 10027 United States
AU: Fleisher, M Q
EM: martyq@ldeo.columbia.edu
AF: The Lamont-Doherty Earth Observatory of Columbia University, 61 Rte. 9W, Palisades, NY 10964 United States
AU: Koutavas, A
EM: koutavas@mit.edu
AF: Department of Earth and Planetary Sciences, Massachusetts Insitute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AB: Records of Biogenic opal, Uranium, Thorium and Protactinium were measured in four cores in the Eastern Equatorial Pacific in order to reconstruct paleoproductivity through the Last Glacial Maximum (LGM) and to test the Silicic Acid Leakage Hypothesis (SALH). The SALH suggests that during the LGM unused silicic acid escaped the Southern Ocean through intermediate and mode waters, and was transported to the equatorial ocean. Previous work indicates that in the presence of excess silicic acid, diatoms are better able to utilize nitrate and other nutrients than cocolithophorids, therefore giving diatoms an ecological advantage. The implications of this include an ecological shift from cocolithophorids to diatoms, and more importantly a drawdown of CO2 from the atmosphere due to calcium carbonate compensation. Furthermore, the SALH predicts a rise in opal burial during the LGM in the equatorial oceans as a result of increased diatom productivity. Preserved biogenic opal was measured in four cores near the Peru margin to test this hypothesis. Additionally, 230Th was used to correct for the effects of sediment focusing, authigenic Uranium was used to indicate periods of reducing conditions characteristic of high-productivity areas, and 231Pa/230Th ratios were used as an indicator of opal and total particle flux. Alkenone data from previous studies were also included. These data do not support the SALH, as there is no evidence for greater opal burial during the LGM in any of the four cores. Furthermore, glacial alkenone fluxes remained high and 231Pa/230Th ratios and Uauth concentrations do not show significant shifts. This suggests that the SALH may not be a sufficient explanation for any drop in atmospheric CO2 levels during the LGM.
DE: 4845 Nutrients and nutrient cycling
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting