Holocene climate and fjord glaciations in Northeast Greenland: implications for IRD deposition in the North Atlantic

摘要

The present distribution in Greenland of iceberg-producing outlet glaciers in the south and floating glaciers with bottom melting in the north is most likely controlled by the large contrast in climate. The Holocene glacial geological record in East Greenland shows that the boundary between the two types of outlet glaciers has moved up and down the coast in response to climate change. The difference in outlet glacier extent and dominant ablation mechanism is determinate for where ice rafted debris (IRD) contained in the bottom layers of the glaciers will be released by bottom melting. The icebergs (ice islands), presently detached from the northern floating glaciers are during long periods retained by semi-permanent sea ice, and will only occasionally escape to the sea. When eventually released, the ice islands contain little―if any―debris, as the debris contained in the bottom layer has already been released by intensive sub-glacial melting during the long stay of the ice-islands in coastal waters. The Holocene glacial geological record from Northeast Greenland is compared to the record of ice rafted debris (IRD) from North Atlantic deep-sea sediment cores. The comparison shows that transport by icebergs in the form of basal debris is unlikely to be the dominant transport mechanism of IRD to deposition sites in the North Atlantic during the Holocene. The ice rafted debris is more likely to be carried at the surface of sea- (or glacier) ice. This supports the result of previous studies by other workers that changes of atmospheric and ocean-surface circulation and temperature are the likely causes of Holocene cycles in IRD concentration in North Atlantic deep-sea sediments.