DETAILED RECORDS OF IRD INPUT INTO THE CENTRAL NORTH ATLANTIC DURING THE LAST GLACIAL CYCLE (MARINE ISOTOPE STAGES 4-1)

High resolution records from North Atlantic deep-sea sediment have been instrumental in documenting millennial-scale climate variations during the last glacial cycle (Marine Isotope Stages (MIS) 4 to 1) including variations of Ice-Rafted Detritus (IRD) concentrations related to massive iceberg discharges from glacial continental ice sheets. We have sampled core VM28-89, located within the Ruddiman IRD Belt in the central North Atlantic at 1 cm intervals and produced detailed records of %IRD ((number of lithic grains >150µm / (number of lithic grains >150µm + number of Planktic foraminifers >150µm)) x 100); lithic grains, >150µm per gram of sediment (lithics/gram); planktic foraminifers, >150µm per gram of sediment (forams/gram), and % coarse fraction for the top 1.20 m.

The %IRD reveals two relatively long intervals of >90% IRD and very low forams/gram between 42-71 cm and 91-113 cm separated by intervals of very low (10-25%) IRD and higher forams/gram. Lithics/gram exhibits much higher frequency fluctuations during these same intervals reaching upwards of 6,000 lithics/gram in the upper long interval and and up to 12,000 lithics/gram in the deeper long interval. Unlike IRD records from farther to the northeast (ODP Site 980 for example), %IRD and lithics/gram show a distinct lack of correlation at higher values. This decoupling is likely due to the effects of significant changes in the input foraminifer shells in the high %IRD intervals.

Our records bear a remarkable resemblance to those from a well-dated core to the west, V23-14 (Hemming & Hajdas, 2003), particularly in %IRD. Tentative correlations of our results to the V23-14 chronostratigraphic framework suggests that our two intervals of very high %IRD correspond to Heinrich Events H2 and H4. The two peaks in %IRD in V23-14 identified as Heinrich Events H1 and H3 are more difficult to identify using our IRD results from VM28-89.