HR: 17:15h
AN: OS24B-02    [Abstracts]
TI: Estimates of glacial Si and N dynamics in the Glacial Southern Ocean using Isotopic Mass balance
AU: * Beucher, C P
EM: beucher@lifesci.ucsb.edu
AF: The Marine Science Institute, University of California Santa Barbara, Santa Barbara, CA 93106,
AU: Brzezinski, M A
EM: brzezins@lifesci.ucsb.edu
AF: The Marine Science Institute, University of California Santa Barbara, Santa Barbara, CA 93106,
AU: Crosta, X
EM: x.crosta@epoc.u-bordeaux1.fr
AF: UMR-CNRS 5805 EPOC, University of Bordeaux I, Talence, 33405, France
AU: Matsumoto, K
EM: katsumi@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455,
AU: Sarmiento, J
EM: jls@Princeton.EDU
AF: Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, NJ 08544,
AB: Evaluating the role of the Southern Ocean in regulating glacial-interglacial atmospheric CO2 cycles remains a major issue in paleoceanography. The Silicic Acid Leakage Hypothesis purports that increases in the export of silicic acid from the Southern Ocean to low latitudes via Subantarctic Mode Water (SAMW) during glacial times enhanced diatom productivity over that of calcifying forms thus contributing to lower atmospheric pCO2 through changes in ocean alkalinity. Recent analyses indicate that the influence of Southern Ocean nutrients on low- latitude alkalinity changes is driven more by changes in the silicic acid : nitrate ratio in SAMW than by the absolute amount of silicic acid exported in this water mass. We present an analysis of the nitrate and silicic acid content of SAMW during the Holocene and the last glacial maximum (LGM) in the Indian sector of the Southern Ocean using records of Si isotopes and diatom-bound N isotopes from the Antarctic and Subantarctic zones. For the LGM diatom-bound N isotopic values combined with Th-corrected opal fluxes suggest a reduction in upwelling in the Antarctic zone to the South of the Polar Front. Si and N isotopes suggest the Subantarctic received considerable silicic acid from the Antarctic, but no nitrate requiring an increase in nutrients supplied by vertical mixing in the Subantarctic to produce the known opal deposit. Depending on the magnitude of the reduction in Antarctic upwelling and the magnitude of the Subantarctic vertical source the ratio of silicic acid:nitrate in SAMW ranged from 0.5 to 6.7 during the LGM. The influence of such changes on atmospheric pCO2 is estimated using numerical modeling .
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 4845 Nutrients and nutrient cycling (0470, 1050)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting