Hays, Burckle, & Isley 9615060 This award supports research to better define the chronology of iceberg calving from Antarctic ice sheets back to oxygen isotope stage 11 (364-423 thousand-years before present (ka)). Re- assessment of published data for sediments deposited during the last 100 ka suggests deposition of ice-rafted debris (IRD) increased dramatically at 17, 22, 63 and 84 ka in the Atlantic and possibly the Indian sectors of the Southern Ocean. The regional extent of these IRD events will be tested, and others will be identified for the last 500 ka by examining the sediment record recovered in curated cores. Age constraints will be provided by biostratigraphy, chemostratigraphy (opal and carbonate records) and oxygen isotope stratigraphy. However, carbon-14 dates (using accelerator mass-spectrometry) will also be acquired in critical cores. The accumulation rate of abiogenic sediment (63 m - 1 mm) will be assessed and its lithology determined to derive IRD accumulation rates. Preliminary mineralogical and geochemical analyses will attempt to trace IRD to their source areas. Findings will yield a high resolution assessment of iceberg calving from Antarctic ice sheets and allow insights to understanding such things as the late Quaternary history of the West Antarctic Ice Sheet. This study will also assess whether Southern Hemisphere ice caps experienced melting episodes at timescales of 2-3 ka, as might be inferred from records of atmospheric temperatures in Antarctic Ice cores. Furthermore, the timing of these Southern Ocean IRD events will be compared with Heinrich Events in the Northern Hemisphere. Preliminary results suggest near-temporal correlations between IRD deposition in the Southern Ocean and Northern Hemisphere Heinrich Events 1, 2, 6 and an un-numbered event at 84 ka. For the two most recent events, Southern Ocean IRD events appear to precede those of the Northern Hemisphere by <3 ka. A finding of strong temporal correlation bet ween iceberg calving in the Northern and Southern Hemispheres would suggest that external forcing rather than internal ice sheet dynamics drove at least some of the Heinrich events. On the other hand, if Southern ocean IRD events preceded those of the Northern Hemisphere, factors other than the North Atlantic salinity oscillator must have impacted global climate at sub-Milankovich timescales.
