Asynchronous deposition of ice-rafted layers in the Nordic seas and North Atlantic Ocean

Instabilities in ice-stream now within the North American Laurentide Ice Sh eet, leading to the periodic release of armadas of icebergs into the North Atlantic Ocean over the past 60,000 years, have produced extensive layers o f coarse-grained iceberg-rafted debris (Heinrich layers) in North Atlantic sediments(1,2). Correlation of these layers with iceberg-discharge events f rom the ice sheets on Greenland, Iceland and Scandinavia, suggested in prev ious studies for some Heinrich layers and in some areas(3-5), would imply t hat ice-sheet instability had been synchronous across the North Atlantic, p resumably in response to a common environmental cause. Here we show a lack of widespread systematic correlations, both between ice-rafted debris layer s in different sediment cores from the Nordic seas, and between the Nordic layers and the North Atlantic Heinrich layers. This suggests that the full- glacial Nordic ice sheets did not exhibit unstable behaviour coincident wit h iceberg discharge from the vast Hudson Bay drainage basin of the Laurenti de Ice Sheet(6,7). Off the Hudson Strait, significant ice-sheet discharge o f melt water is indicated by size-sorted sandy and muddy turbidite sediment s, different from the poorly sorted debris flows which dominate sedimentati on on the margins of the Nordic seas(8-10). Together, these results suggest that the dynamics of Quaternary ice sheets surrounding the Nordic seas wer e different from the outlet glacier draining the Hudson Bay basin, and they provide evidence against a common circum-North-Atlantic mechanism driving the discharge of icebergs.