HR: 1340h
AN: PP23B-1407    [Abstracts]
TI: A ~100 Kyr SST record based on the Mg/Ca of Neogloboquadrina pachyderma (s) from the Labrador Sea.
AU: * Rashid, H
EM: hrashid@seas.marine.usf.edu
AF: University of South Florida, 140 7th Avenue South, St. Petersburg, FL 33701 United States
AU: * Rashid, H
EM: hrashid@seas.marine.usf.edu
AF: Massachusetts Institute of Technology, 77 Mass. Avenue, Cambridge, MA 02139 United States
AU: Boyle, E
EM: eaboyle@mit.edu
AF: Massachusetts Institute of Technology, 77 Mass. Avenue, Cambridge, MA 02139 United States
AB: Core Hu90013-29[58\deg23.61N; 56\deg45.76E] was retrieved at 2918m water depth from the Labrador Rise of the Eastern Canadian continental margin in front of the mouth of the Hudson Strait. We measured the Mg/Ca ratio and $\delta$ $^{18}$ O in the polar species planktonic foraminifera {\it Neogloboquadrina pachyderma} (sinistral) to reconstruct a sea surface temperature (SST) of the past 100kyr. A modified version of the Boyle and Keigwin (1985/6) cleaning method comprising mechanical, oxidative and reductive cleaning was employed to clean the foraminiferal shell fragments. Mg/Ca ratios range from 0.35 to 1.55mmole/mole corresponding to -3 to 11\deg C temperature using the calibration curve of N\"{u}rnberg {\it et al}.(1996) were obtained. Core top Mg/Ca ratio of 1.4mmole/mole corresponds to summer (August) SST of ~10\deg C at the site. The reconstructed SST-curve is not as high resolution as the oxygen isotope curve due to the dearth of foraminifera; however, we observe high frequency SST variability during Marine Isotope Stage 3. Calculated SST has rise from -3 to 8\deg C at the end of Heinrich events except during Heinrich event 2. The cooler temperature values (below the freezing point of seawater) are suspected to be an artifact of the exponential function of the N\"{u}rnberg {\it et al}. (1996) calibration equation, because under very cold conditions {\it N. pachyderma} (s) would live under stress and its calcification temperature may deeper than their normal depth of habitation (Kohfeld {\it et al}.1996). An SST of ~-1\deg C was reconstructed for the Last Glacial Maximum (LGM) suggesting an ice-free condition during the summer (August) as required for the {\it N. pachyderma} (s) bloom. Our results contrast with the suggestion of a permanent sea-ice cover during the LGM by deVernal {\it et al}.(2000) and Levac {\it et al}.(2001). Moreover these authors reported a SST of ~16\deg C compared to this study (~12\deg C) during the early to mid Holocene, which seems too warm for such Northern latitudes.
DE: 4825 Geochemistry
DE: 4870 Stable isotopes
DE: 4267 Paleoceanography
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1065 Trace elements (3670)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting