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

Abstract

Instabilities in ice-stream flow within the North American Laurentide Ice Sheet, leading to the periodic release of armadas of icebergs into the North Atlantic Ocean over the past 60,000 years, have produced extensive layers of coarse-grained iceberg-rafted debris (Heinrich layers) in North Atlantic sediments1,2. Correlation of these layers with iceberg-discharge events from the ice sheets on Greenland, Iceland and Scandinavia, suggested in previous studies for some Heinrich layers and in some areas3,4,5, would imply that ice-sheet instability had been synchronous across the North Atlantic, presumably in response to a common environmental cause. Here we show a lack of widespread systematic correlations, both between ice-rafted debris layers 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 with iceberg discharge from the vast Hudson Bay drainage basin of the Laurentide Ice Sheet6,7. Off the Hudson Strait, significant ice-sheet discharge of melt water is indicated by size-sorted sandy and muddy turbidite sediments, different from the poorly sorted debris flows which dominate sedimentation on the margins of the Nordic seas8,9,10. Together, these results suggest that the dynamics of Quaternary ice sheets surrounding the Nordic seas were 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.