INITIATION OF FENNOSCANDIAN ICE-SHEET RETREAT DURING THE LAST DEGLACIATION

ALTHOUGH the retreat history of the southern margin of the Laurentide ice sheet during the last deglaciation has been well known for several decades 1-3 and recently supported by evidence from accelerator mass spectrometer (AMS) radiocarbon dating of meltwater in the Gulf of Mexico 4 and the North Atlantic subtropical gyre 5, the retreat history of the Fennoscandian ice sheet before 13 kyr ago is still poorly documented. From AMS C-14 dating and isotopic analysis of a rapidly deposited series of supratill sediments in the Norwegian Channel (North Sea), we find that the southern margin of the Fennoscandian ice sheet was in retreat by 15 kyr BP (before present), approximately 2,000 yr earlier than previously supposed. Oxygen isotope analyses in the channel sediments confirm earlier evidence from deep Norwegian Sea sediment cores for low salinity due to ice sheet discharge beginning approximately 15-14.5 kyr BP (ref. 6). Recent recalibration of the C-14 timescale indicates that the onset of deglaciation within the Norwegian Sea occurred during an interval of rapidly increasing summer insolation beginning approximately 18,000 calendar yr BP (ref. 7), suggesting that ice-sheet retreat may have been caused by increasing insolation acting on a particularly climate-sensitive ice-sheet configuration. Fresh water and icebergs discharged into the Norwegian Sea at this time reached the North Atlantic and may have contributed to a brief interval of extreme oceanic cooling 8 and reduced production of North Atlantic Deep Water 9,10. These factors may also have helped to briefly reverse the deglaciation trend (Erie Interstade) already underway in North America.