Paleoclimate archives indicate that Marine Isotope Stage (MIS 3) was characterized by a highly variable climate, expressed in the Greenland ice cores as large temperature fluctuations associated with Dansgaard-Oeschger (D-O) cycles(Johnsen et al., 2001). However, an important 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 (Birchfield and Broecker, 1990; Broecker et al., 1990; Zaucker and Broecker, 1992).

In order to investigate the relationship between Gulf Stream salinity variation and D-O cyles, we combine Mg/Ca measurements (a proxy for the temperature of calcification) with d18O analyses of shells from the surface-dwelling foraminifera Globigerinoides ruber from ODP site 1060 located beneath the Gulf Stream on the Blake Outer Ridge (36.77&Mac251;N, 74.47&Mac251;W; 3480 m; 20-53 cm/kyr sed. rate) to produce a high-resolution record of d¹⁸O_SEAWATER (d¹⁸O_SW) during MIS 3 (49.5 – 59.2 kyr).

The Mg/Ca-temperature (SST) record from 1060 shows minimal variability (±3&Mac251;C) between stadials and interstadials. Average interstadial Mg/Ca-SSTs (25.2&Mac251;C) agree with faunal August SST reconstructions(Vautravers and Shackleton, 2004), but stadial Mg/Ca-SST reconstructions are several degrees warmer than faunal estimates. The calculated d¹⁸O_SW record covaries with Greenland ice core d¹⁸O values (Johnsen et al., 2001), and indicate high salinities similar to coeval Caribbean salinity reconstructions(Schmidt et al., 2004) during stadials followed by abrupt decreases up to 0.9‰ occurring in less than 250 years on the transition to interstadials.

We hypothesize that the input of isotopically light melt water from the southeast coast of North America due to continental ice sheet retreat during interstadials accounts for the rapid and large decrease in Gulf Stream salinity. Covariation between our d¹⁸O_SW record and the Greenland ice core d¹⁸O record suggests that glacial Gulf Stream salinity is sensitive to D-O cycles, increasing during stadials and rapidly decreasing in response to Northern Hemisphere warming.

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