HR: 1340h
AN: PP13B-1263    [Abstracts]
TI: Opal burial in the Pacific Southern Ocean since the LGM: Implications for ocean circulation and nutrient cycles
AU: * Bradtmiller, L I
EM: louisab@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Rte. 9W, Palisades, NY 10964, United States
AU: * Bradtmiller, L I
EM: louisab@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences, Columbia University, 2960 Broadway, New York, NY 10027, United States
AU: Anderson, R F
EM: boba@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Rte. 9W, Palisades, NY 10964, United States
AU: Anderson, R F
EM: boba@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences, Columbia University, 2960 Broadway, New York, NY 10027, United States
AU: Fleisher, M Q
EM: martyq@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Rte. 9W, Palisades, NY 10964, United States
AU: Burckle, L H
EM: burckle@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Rte. 9W, Palisades, NY 10964, United States
AB: ²³⁰Th-normalized opal fluxes and ²³¹Pa/²³⁰Th ratios were measured in over fifty cores in the Southern Pacific Ocean (100°W-160°W, 56°S-64°S) to reconstruct diatom 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 oceans. The implications of this include an ecological shift in tropical regions from cocolithophorids to diatoms (and therefore increased LGM opal burial relative to the Holocene), and a drawdown of atmospheric CO2 due to calcium carbonate compensation. Conversely, the SALH predicts decreased total opal burial during the LGM in the Southern Ocean, as a result of silicic acid export to the tropics. Data from previous studies of the equatorial Pacific are not consistent with the SALH, in that they shows decreased LGM opal burial relative to the Holocene in most cores studied. Most Atlantic data, however, show increased LGM opal burial. Considering areas of equal size, the magnitudes of increased Atlantic and decreased Pacific LGM opal burial are equal (within error), implying some large-scale redistribution of silicic acid. Any mechanism to explain these opposite patterns is likely to be found in the Southern Ocean, as it is the direct connection between the two basins. A few distinct trends emerge in the South Pacific data. First, opal burial generally decreases from west to east. Second, the pattern of opal burial across the Antarctic Polar Front (APF) during the LGM is the opposite of that during the Holocene. Holocene opal burial is greatest south of the modern APF, while LGM opal burial was greatest north of the APF. However, while opal burial shifted north during the LGM, total opal burial in the Pacific Southern Ocean appears to have been less than today, consistent with the predictions of the SALH. Further implications for the SALH will be discussed, including the relationship of the Southern Ocean to the tropics, and what this relationship implies about ocean circulation over the last glacial-interglacial transition.
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 4825 Geochemistry
DE: 4845 Nutrients and nutrient cycling (0470, 1050)
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4926 Glacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting