The Greenland ice sheet - a model for its culmination and decay during and after the last glacial maximum

Abstract

Ice margin reconstructions of the Greenland ice sheet during LGM (c. 21-16 ka) and 10 ka are based on published onshore field evidence supplemented with recent studies on the East Greenland shelf and results of current field work in the Scoresby Sund area Additional evidence comes from the pattern of Holocene uplift and the frequency distribution of more than 1000 14C-dates. During LGM, only southern Greenland (south of lat. 69°-72°N) saw a major expansion of the ice sheet with thick cover over the present coastline and onto the shelf. In the north, outlet glaciers filled fjord basins, including the Nares Strait between Canada and Greenland, and piedmont glaciers descended from coastal mountains onto the coastline, but the glaciers did not cover the shelf. Break up probably began after c. 15 ka, and took place in two discrete steps. First, the shelf and major inlets were cleared of marine based ice. There was little thinning of the ice on land, and in the northern parts there was little change at all. The driving factor during this step was calving caused by rising sea level. This lasted until c. 10 ka, but may have been consumated before the Younger Dry as. The second step began with a glacier-readvance between 10 and 9.5 ka, and after this the fjord glaciers began to retreat rapidly. Within a few millenia all the presently ice free land was exposed. The frequency distribution of 14C-dates show that the nearshore marine and terrestrial biotopes emerged in this period. The discharge of ice was both by calving and melting, and the driving force was probably increased insolation. Maximum Holocene uplift was attained in areas of the 10 ka ice margin, indicating that the uplift is essentially a response to the melting and unloading of ice that began at this time. In suppport of this, recent results in West, North and East Greenland indicate that the age of the marine limits decline towards the outer coasts, away from the 10 ka ice margin.