DETAILED RECORDS OF THE ICE-RAFTED DETRITUS IN SEDIMENTS FROM THE ORPHAN KNOLL, NORTHWEST ATLANTIC OCEAN

The detrital layers found in sediments from Orphan Knoll, Northwest Atlantic Ocean, are analogous to Heinrich layers found in central Atlantic Ocean deep-sea sediments that were deposited during the recent glacial cycle. Two 5-meter cores (DVY081-GVY001 and DVY081-GVY002 found at water depths of 3,721 meters and 1,170 meters respectively) were recovered from Orphan Knoll during cruise RRS Discovery Cruise ICY-LAB (2017). Detailed Ca/Sr XRF count ratios have been generated for both cores. Cores GVY002 and GVY001 have been sampled at 2 centimeter intervals in order to generate two proxies for the input of ice-rafted detritus (IRD): 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 (forams), >150 μm)) X 100.

The top 110 centimeters of IRD records for GVY002 reveal 5 distinct peaks in IRD input, each between 4000-6500 lithics/gram. Three of these peaks coincide with three peaks in the Ca/Sr ratios in the upper meter indicative of dolomite rich IRD from the Canadian margin.

The IRD record and Ca/Sr ratio record generated in this study, when compared to the previously generated similar records in GVY001, reveals a similar pattern but over a much longer downcore sediment interval (over the upper 4.5 meters in GVY001 versus the upper 1.8 meters in GVY002). This is due to the higher sedimentation rate in GVY001. Hendry, et al. (2019) tentatively correlated the shallowest peaks in Ca/Sr ratios with Heinrich Events H0 - H4 by correlating the Ca/Sr ratio records in GVY001 to the δ¹⁸O record of N. pachyderma (s.). An IRD peak in GVY001 corresponds to each of the Heinrich Events identified in Hendry, et al. (2019). Subsequent comparison of GVY002 IRD records with those of GVY001 suggest that Heinrich Events H0, H1, and H2 can be identified over the first meter. Both GVY002 and GVY001 display two additional IRD peaks of at least 4000 lithics/gram between H1 and H2 during intervals of very low Ca/Sr ratios.