HR: 17:15h
AN: PP44A-06    [Abstracts]
TI: Gulf Stream Salinity Variation During MIS 3 and its Link to D-O Cycles
AU: * Schmidt, M W
EM: schmidt@geology.ucdavis.edu
AF: University of California Davis, Department of Geology, Davis, CA 95616 United States
AU: Vautravers, M J
EM: mv217@pop.hermes.cam.ac.uk
AF: Godwin Laboratory, University of Cambridge, Department of Earth Sciences, Cambridge, CB3 2SA United Kingdom
AU: Spero, H J
EM: spero@geology.ucdavis.edu
AF: University of California Davis, Department of Geology, Davis, CA 95616 United States
AB: Paleoclimate archives indicate that Marine Isotope Stage 3 (MIS 3) was characterized by a highly variable climate, expressed in the Greenland ice cores by the Dansgaard-Oeschger (D-O) fluctuations associated with large temperature changes (Johnsen et al., 2001). However, the question remains as to the trigger for these abrupt Northern Hemisphere climate swings. A popular theory implicates thermohaline circulation instability as a driver for D-O cycles, suggesting that salinity variability in surface waters delivered to the sub-polar North Atlantic via the Gulf Stream may have played a role in driving millennial-scale oscillations in glacial thermohaline circulation (Broecker et al., 1990; Zaucker and Broecker, 1992). In order to investigate the relationship between Gulf Stream salinity variation and D-O cycles, we combine Mg/Ca measurements (a proxy for the temperature of calcification) with ($\delta$$^{18}$O) analyses of shells from the surface-dwelling foraminifera {\it Globigerinoides ruber} (white var.) from ODP site 1060 located beneath the Gulf Stream on the Blake Outer Ridge (36.77$\deg$N, 74.47$\deg$W; 3480 m; 20-53 cm/kyr sed. rate) to produce a high-resolution record of $\delta$$^{18}$O$_{SEAWATER}$ ($\delta$$^{18}$O$_{SW}$) during MIS 3 (49.5- 59.2 kyr, corresponding to Interstadial 13 to 16 on the SSO9sea time scale). The Mg/Ca-temperature (SST) record from 1060 shows minimal variability ($\pm$3$\deg$C) between stadials and interstadials. Average interstadial Mg/Ca-SSTs (25.2$\deg$C) agree with faunal August SST reconstructions (Vautravers et al., 2004), but stadial Mg/Ca-SST reconstructions are warmer than faunal estimates. The calculated $\delta$$^{18}$O$_{SW}$ record co-varies with the Greenland ice core $\delta$$^{18}$O record (Johnsen et al., 2001), and indicates high stadial salinities, similar to MIS 3 Caribbean salinity reconstructions (Schmidt et al., 2004), followed by abrupt decreases in $\delta$$^{18}$O$_{SW}$ up to 0.9$\permil$ occurring in less than 250 years on the transition to interstadials. We hypothesize that the input of isotopically light freshwater from melting North American ice sheets during interstadials accounts for the rapid, large decrease in Gulf Stream $\delta$$^{18}$O$_{SW}$. Our $\delta$$^{18}$O$_{SW}$ reconstruction from ODP 1060 therefore suggests that D-O cycles directly impact Gulf Stream salinity during MIS 3, with elevated salinities occurring during stadials followed by a rapid decrease of salinity into interstadials in response to Northern Hemisphere warming.
DE: 4215 Climate and interannual variability (3309)
DE: 4267 Paleoceanography
DE: 1620 Climate dynamics (3309)
DE: 1655 Water cycles (1836)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting