HR: 0800h
AN: PP11B-1461    [Abstracts]
TI: Intermediate Water Changes Across the Oxygen Minimum Zone During the Last 50,000 Years, Southern California Margin
AU: * Murphy, D P
EM: dmurphy@umail.ucsb.edu
AF: University of California, Santa Barbara, Department of Geological Sciences, Santa Barbara, CA 93106-9630 United States
AU: Kennett, J P
EM: kennett@geol.ucsb.edu
AF: University of California, Santa Barbara, Department of Geological Sciences, Santa Barbara, CA 93106-9630 United States
AU: Southon, J R
EM: jsouthon@uci.edu
AF: University of California, Irvine, Earth System Science Dept B321 Croul Hall, Irvine, CA 92697-3100 United States
AB: The Oxygen Minimum Zone (OMZ) off S. California, currently at water depths of 500 - 1000m, has been shown to fluctuate on orbital and millennial time scales. Knowledge of the changing strength of the OMZ is limited to two cores from ~600m and ~950m (ODP Holes 893 and 1017). During interglacials, the OMZ is present in both cores; during glacial it is absent in both. Previous workers have interpreted this in part to a switching of source waters from young, O2-rich North Pacific Intermediate Water, to the older O2-poor Southern Component Water (SCW). Benthic foraminifera are sensitive recorders of the oxygenation state of bottom waters. We employ stable oxygen isotopes to determine if temperature shifts occurred along with benthic faunal changes to test the hypothesis that intermediate water ventilation shifts with changes in oxygenation. We sampled four cores, from the open continental slope near Point Conception from water depths between 585 - 755m, currently bathed by SCW. Chronologies were established by stable isotope stratigraphy tied with 22 14C dates. Sampling resolution is between 270 - 1,140 yrs/sample. Planktonic and Benthic d18O records have been constructed, and benthic foraminiferal faunal changes documented. Benthic faunal changes fluctuated on orbital time scales within the OMZ. Planktonic d18O oscillations, provide climatic records on orbital and millennial time scales. On orbital time scales, the benthic records show a decrease of 1.6‰ across the last glacial termination, implying an increase of 1-2 deg C beyond the ice volume effect. On millennial scales, the two deepest benthic d18O records demonstrate oscillations across Marine Isotope Stage 3 of ~0.25‰ that coincide with interstadials seen in the planktonics. Their presence indicates that intermediate water sources oscillate on millennial as on orbital time scales within the OMZ. The absence of the OMZ during glacial periods followed by its strengthening and an increase in bottom water temperatures implies that ventilation changes effected intermediate water oxygenation.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4926 Glacial
DE: 4936 Interglacial
DE: 4940 Isotopic stage
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005