HR: 0800h
AN: PP51B-0479    [Abstracts]
TI: Oxygen isotopes of Pacific seawater, 0-40 kyr, based on d18O and Mg/Ca of benthic and planktic foraminifera: relation to deglacial sealevel rise.
AU: * Mix, A C
EM: mix@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic & Atmos. Sciences COAS Admin. Building 104, Corvallis, OR 97331-5503, United States
AU: Klinkhammer, G P
EM: gklinkhammer@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic & Atmos. Sciences COAS Admin. Building 104, Corvallis, OR 97331-5503, United States
AB: Combining high resolution (~200 year sample resolution) oxygen and carbon isotope measurements and Mg/Ca analyses in planktic (G. ruber and N. dutertrei) and benthic foraminifera (Uvigerina sp.; use of infaunal benthics minimizes likely CO3= effects) from the mid-depth eastern Pacific provides for detailed estimates of changing d18O of seawater over the past 40 kyr at ODP Site 1242. The key to this analysis is improved precision of the Mg/Ca analyses based on a new generation of high precision flow-through time-resolved analysis (FT-TRA) (e.g., average internal precision for Mg/Ca is now +/-0.005 benthic, and +/-0.015 planktic). This method is relatively insensitive to mild dissolution of heterogeneous shells, and thus requires no corrections for preservation. The change in seawater d18O (at 1364 m depth) between the Holocene and Last Glacial Maximum is 1.2 +/- 0.04 permil when averaged over the stages, consistent with pore-water diffusion estimates; however, millennial scale events (which the pore-water data cannot detect) bring the total range up to about 1.6 permil. Are such short-term events related to sealevel change, or do they reflect changing watermasses? Measurements of d13C data (C. wuellerstorfi), sensitive to modern subsurface watermass gradients, are not highly correlated to short- term changes in d18Oseawater suggesting a transient response to ice volume changes. Glacial weakening of AAIW (salty, high d18O, high d13C) relative to north Pacific watermasses (fresher, lower d18O, low d13C) suggest that the benthic d18Oseawater may underestimate total local changes related to ice volume (with a caveat regarding proper scaling of benthic Mg/Ca to temperature). Benthic d18Oseawater falls through the deglaciation in steps, starting at 18 cal ka, with maximum rates of change at 14-15 ka, and with secondary rapid steps at 16-17 ka and 10-11 kar. Planktic foraminifera yield smaller glacial-interglacial d18Oseawater values, with Holocene-to-LGM stage- average changes of 1.04 +/- .06 for surface-dwelling G. ruber (with significant temperature changes recorded by Mg/Ca) and 1.12 +/-0.03 for thermocline-dwelling N. dutertrei (with essentially no temperature changes recorded by Mg/Ca). Changes lower than the benthic seawater estimates suggest slight glacial freshening of the Eastern Pacific Warm Pool. Millennial scale changes are also superimposed on the planktic data, with variations on the scale of 4-5 kyr in both Holocene and LGM time.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 3036 Ocean drilling
DE: 4926 Glacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting