A model of Weichselian glacier variation in the North Atlantic region |
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| Authors: | GEOFFREY S BOULTON |
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| Institution: | School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, England;17th November, 1978. |
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| Abstract: | The evidence for the extent and timing of Weichselian glaciation in Arctic regions shows that: (1) there were no major marine ice domes in the Arctic at 18,000 B.P. but that glaciers were relatively limited in extent; (2) there were no extensive ice shelves at 18,000 B.P. as envisaged by Hughes, Denton & Grosswald(1977); (3) the major periods of glacier expansion were between 125,000 and 80,000 B.P., just prior to 45,000 B.P., and between 11,000 and 8,000 B.P., and thus that glacier fluctuations at the southern margins of the Laurentide and Fennoscandian ice sheets were out of phase with those in the Arctic which advanced during southern interstadials. Phases of glacier advance in the Atlantic sector of the Arctic can be identified in deep sea cores by the peaks in concentration of iceberg-dropped detritus and an increase in sedimentation rates, which are highest when sub-polar water penetrates to the north. The key to the temporal pattern of Arctic glaciation and its association with oceanic changes is given by the intimate association of present-day Arctic glacierisation with the two major low pressure troughs which penetrate the Arctic in the Atlantic sector and in Baffin Bay. The chronology of glaciation in the Atlantic sector is associated with the activity of these troughs and the related oceanic circulation. Cooling of the Arctic due to reduction in solar radiation at the end of the last interglacial, when the pack ice lay north of 75d?N in the Atlantic, produced ideal conditions for Arctic glacier growth, with moisture transported by a strong cyclonic flux into a cooling Arctic from a strong North Atlantic Drift current. A positive feedback loop involving ocean and atmospheric circulation and pack ice, caused movement of the polar front to the south, thus slowly cutting off the supply of moisture to the Arctic. Further cooling at 75,000 B.P. caused a rapid extension of the polar front south of 45d?N, effectively cut off the northward movement of surface currents on the North Atlantic, and produced a strong zonal oceanic and atmospheric circulation which starved Arctic glaciers of nourishment and caused their retreat, and initiated rapid build up of the Fennoscandian and Laurentide ice sheets. Subsequent extensions of Arctic glaciers were associated with limited northward movement of sub-polar water and associated Atlantic depressions. The expansion of glaciers within the Arctic between 11,000 and 8,000 B.P. was associated with the first and diachronous penetration of moisture into a still cool Arctic during decay of the two great ice sheets. |
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