"CANADIAN" RADIOGENIC ISOTOPE SIGNATURE OF YOUNGER DRYAS AGE ICE-RAFTED SEDIMENTS IN SEDIMENTARY SEQUENCES FROM LOMONOSOV RIDGE AND FRAM STRAIT

The Younger Dryas (YD) cooling event and the related slowing of the Atlantic Meridional Overturning Circulation (AMOC) have been linked to a large array of processes. Thee most widely supported causal mechanism involves an influx of freshwater into the North Atlantic Ocean linked to a partial drainage of glacial Lake Agassiz. Recently, a northward drainage route, through the Mackenzie River outlet into the Arctic Ocean, has been suggested from land-based studies [Murton et al., Nature 464, 740-743]. Sedimentological and geochemical analysis of cores raised from Lomonosov Ridge and the Fram Strait area, yield relatively robust evidence for enhanced ice-rafting deposition -IRD- (with a 5-fold increase -) during the critical interval. At Lomonosov, the corresponding sedimentary layer (from ca. 13 to 12 ka) is marked by a pulse of detrital carbonates in the silt to sand fractions, with approximately equal amounts of calcite and dolomite, pointing towards an Arctic Canadian sediment source area. The layer also depicts a 5 fold increase 230Th-excess, which we link to an enhanced flux of scavenging particles. Here, we examine further the geochemical signatures of the YD-layer based on elemental (Zr/Al) and isotopic (Sr, Nd and Pb) data on bulk sediments and residues ensuing from the removal of exchangeable fractions (Zr/Al, Nd, Pb, Sr), thought to label detrital sediment source areas. Based on a survey of literature we broadly identify three major source areas variably contributing to IRD during the MIS 3-Present interval: the Russian, Canadian and Greenland margins. The YD interval is particularly highlighted by strong elemental and isotopic excursions, notably a peak in radiogenic Sr, indicating prominent supplies from the Canadian end-member. This suggests enhanced sea-ice production and drifting along the Beauford Gyre. A major drainage event along the Mackenzie outlet area, as proposed in the above reference, would be a suitable trigger for enhanced sea-ice production, leading to the nearly 5-fold export of Arctic sea-ice suggested by our data. As already proposed by Tarasov and Peltier [Nature 435, 662-665], such a routing of freshwater would have been very efficient in reducing the AMOC in the Greenland, Iceland and Norwegian seas, and/or in the North Atlantic area south of the Denmark, Iceland-Faroe-Scotland, sills.