HR: 16:00h
AN: OS34A-01 INVITED     [Abstracts]
TI: Biogenic Opal Deposition in the Eastern Equatorial Pacific Over the Last 300 Kyrs: Silica Leakage Revisited
AU: * Kienast, S S
EM: skienast@whoi.edu
AF: Oceanography, Dalhousie University, 1355 Oxford Street, Halifax, NS B3H 4J1 Canada
AU: Kienast, M
EM: makurs.kienast@dal.ca
AF: Oceanography, Dalhousie University, 1355 Oxford Street, Halifax, NS B3H 4J1 Canada
AU: Francois, R
EM: rfrancoi@eos.ubc.ca
AF: Eart and Ocean Sciences, University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4 Canada
AU: Calvert, S E
EM: scalvert @eos.ubc.ca
AF: Eart and Ocean Sciences, University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4 Canada
AU: Brzezinski, M
EM: brzezins@lifesci.ucsb.edu
AF: Ecology Evolution and Marine Biology, University of California, Marine Biottechnology Lab, Room 3149, Santa Barbara, CA 93106 United States
AB: The Eastern Equatorial Pacific (EEP) plays an important role in the present day carbon cycle and there is increasing evidence that primary productivity in this region is linked to Southern Ocean processes via the circulation of Subantarctic Mode Waters and their preformed nutrient content. In order to examine these links and their possible contribution to ecosystem and climate change in the past, we determined biogenic opal along with the constant flux tracer ²³⁰Th and the Pa/Th{(xs,0)} ratio in several sediment cores from the EEP (80°W to 110°W). At 110°W, ²³⁰Th normalized opal fluxes and Pa/Th{(xs,0)} ratios increase from lower levels during the last glacial period (OIS 2) to higher levels during the Holocene, suggesting that opal export to the sea floor was lower under glacial conditions. Between 80° and 90°W, on the other hand, ²³⁰Th normalized opal fluxes and Pa/Th ratios show elevated values during the last glacial termination compared to the Holocene and OIS 2. These findings are counter to the predication that excess silicic acid generated during OIS2 in the Antarctic sector of the Southern Ocean leaked into the lower latitudes (the silica leakage hypothesis), leading to an ecosystem shift towards opal producing phytoplankton there, which could have contributed to the drawdown of atmospheric CO₂ during cold periods. However, very distinct opal flux maxima occur between 40-60 kyrs and 250-300 kyrs B.P. in the EEP with amplitudes far exceeding those observed in the younger parts of the records. Comparison with opal records from the Southern Ocean suggests that the opal maxima in the EEP correspond to relative minima in opal deposition in the Subantarctic zone of the Southern Ocean. This suggests that in order for silica leakage into the EEP to occur, excess silicic acid generated in the Antarctic zone during cold periods must escape biological uptake in the Subantarctic region, and we propose that this only occurred between 40-60 kyrs (OIS 3) and 250-300 kyrs (OIS 8) when atmospheric dust deposition was reduced and coincided with extensive ice cover in the Southern Ocean.
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4924 Geochemical tracers
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005