Records of The Last Glacial Influx of Ice-rafted Detritus at Site DY081-GVY002, On the Orphan Knoll, Northwest Atlantic Ocean.

Abstract

Records of The Last Glacial Influx of Ice-rafted Detritus at Site DY081-GVY002, On the Orphan Knoll, Northwest Atlantic Ocean. Hannah E. Gonsalves*, James L. Cullen, Department of Geological Sciences, Salem State University, 352 Lafayette Street, Salem, MA, 01970. *H_gonsalves@salemstate.edu Detrital layers attributed to increases in influx of ice rafted detritus (IRD) found in sediments from the Orphan Knoll, Northwest Atlantic Ocean, are very similar to Heinrich layers (Heinrich, 1988) found in glacial sediments from the central Atlantic Ocean. A five meter core at 1,170 meters water depth on the Orphan Knoll was recovered during cruise RRS Discovery Cruise ICY-LAB (2017). We have used 30 samples at 5 cm intervals to extend our previously presented IRD records (Alisha Guglielmi, 2020) into the earlier part of the last glacial (Marine Isotope Stage 3) by generating two proxies of IRD input: number of lithic fragments >150 μm per gram sediment (lithics/gram) and % IRD (number of lithic grains, >150 μm / (number of lithic grains, >150 μm + number of whole planktic foraminifers, >150 μm)) X 100). Our additional one meter (130-230 centimeters) reveals 2 additional peaks of greater than 5,000 lithic grains per gram at 155 cm and 195 cm. The additional meter also records three intervals of high % IRD at 130-140 cm, 160-180 cm, and 205-220 cm. The % IRD intervals correlate with intervals of high Ca/Sr ratios in the core, a proxy that has been previously used to indicate the input of detrital carbonate grains composed of dolomite and/or inorganic calcite. We have preliminarily correlated these three intervals with Heinrich events H3, H4, and H5. The peaks in IRD/gram recorded in our extended record seem to be completely decoupled from the other two proxies, occurring at depths recording low values of %IRD and low Ca/Sr ratios for reasons we have not yet been able to explain.