A Late Glacial to Holocene Sediment Record of Ice-Rafted Detritus from Orphan Knoll, Northwest Atlantic Ocean

Abstract

High-resolution sediment records from North Atlantic deep-sea sediments have been used to document millennial-scale abrupt climate oscillations during the last glacial cycle. A five-meter core (DY081-GVY002) was recovered from the Orphan Knoll, Northwest Atlantic Ocean during the RRS Discovery Cruise ICY LAB in 2017. Forty-closely spaced samples from the top 65cm (1-2 cm spacing) have been used to generate two proxies that record changes in the input of ice-rafted detritus (IRD): IRD/g, lithic grains >150µm per gram of sediment, %IRD ((number of lithic grains >150µm) / (number of lithic grains >150µm + number of planktic foraminifers >150µm)) x 100). Our record, which significantly improves the resolution previously presented by Gugliemli et al. (2020), reveals a series of abrupt increases in IRD input ranging from 4,000-7,200 lithic grains/g within a background of 3,000 or less lithic grains/g, at 5cm, 10cm, 25cm, 38cm and 44cm. The %IRD record reveals high values over the interval of 34cm-55cm that correspond to high IRD/g input which can be correlated to an interval of high Ca/Sr ratios, a proxy that has been previously used to indicate the input of detrital carbonates composed of dolomite and/or inorganic calcite (Hodell et al. 2008). We have preliminarily correlated this interval to Heinrich event 1 (H1), one of a series of abrupt increases in IRD input that occurred throughout the North Atlantic during the last glacial (MIS 4-2); (Heinrich 1988). Another high interval in the Ca/Sr ratio occurs at 12-15cm this corresponds to a peak in %IRD, we have preliminarily correlated this interval as Heinrich event 0 (H0). Our data suggests a closer relationship between %IRD and Ca/Sr proxies, whereas IRD/g is more easily influenced by other factors. The other peaks in IRD/g that also record low %IRD occur when Ca/Sr ratios are at lower background levels, suggesting the decoupling of these proxies for reasons we have not been able to explain yet.