CORRELATION OF ICE-RAFTED DETRITUS IN SOUTH ATLANTIC SEDIMENTS WITH POLAR ICE: IMPLICATIONS FOR INTERHEMISPHERIC MILLENNIAL CLIMATE CHANGE DURING THE LAST GLACIAL PERIOD

Previous study of ice-rafted detritus (IRD) in high-sedimentation-rate cores from the South Atlantic identified six to seven discrete episodes of IRD deposition, recurring on millennial time scales during the last glacial period (Kanfoush et al., 2000). Many questions remain, however, regarding the origin of these South Atlantic IRD (SA-IRD) events, their significance for Antarctic ice-sheet dynamics, and their exact relationship to millennial-scale climate events recorded in polar ice cores. Here we correlated a marine sediment core (TTN057-21) containing the SA-IRD events to polar ice core records from Greenland and Antarctica using two independent methods: benthic and planktic stable isotopes (Charles et al., 1996 and Mortyn et al., in press, respectively) and geomagnetic paleointensity (Channell et al., 2000; Stoner et al., 2002). The paleointensity-assisted correlation supports the isotopic correlations between TTN057-21 and polar ice cores, permitting us to place SA-IRD events in the context of polar climate change in both hemispheres.

During marine isotopic stage (MIS) 3, SA-IRD events generally coincided with warm interstadials in Greenland and with cooling following prominent warm events (A1-A4) in Antarctica. This anti-phase behavior is best illustrated for the last deglaciation when a prominent SA-IRD event (SA-0) occurred during the Antarctic Cold Reversal at the same time as a prominent warming (Bolling-Allerod) in Greenland. Moreover, SA-IRD events appear to coincide with sea-level highstands recorded on the Huon Peninsula during the last deglaciation (MWP-1A) and MIS 3 (U-Th dated at 30.4, 38.3, 43.7, 51.5 ka) (Yokoyama et al., 2001). The latter observation implies that rising sea level may have triggered SA-IRD events by unpinning grounded ice masses in the Weddell Sea region that had previously expanded onto the continental shelf during stadial periods. The rapid disintegration of these ice masses led to massive discharges of debris-laden bergs to the South Atlantic that, in turn, had a chilling effect on Southern Ocean surface temperatures.