Processes of buildup and retreat of the Greenland Ice Sheet

Abstract

Sensitivity experiments were conducted to study the influence of several physical processes on the evolution of the Greenland ice sheet over the last 250,000 years. The experiments were carried out by means of a three‐dimensional thermodynamical model. The mass balance is modeled by a surface energy balance model. This means that variations in orbital parameters following from the astronomical (Milankovitch) theory can be incorporated in the ablation calculations. It is shown that with regard to the Greenland ice sheet, variations in shortwave radiation are only of minor importance for the changes in volume over time. Calculations of the various components of the energy balance under glacial and interglacial conditions show that the changes in absorbed shortwave radiation resulting from changes in orbital parameters are considerably smaller than the variations in the sensible heat flux caused by temperature variations. Thermodynamics are only of importance for the volume changes of the ice sheet if the climate, is on average, stable over a long period. In between 110 kyr B.P. and 20 kyr B.P. the ice volume increased slowly due to the cooling of the ice, which resulted in a higher effective viscosity and thus a thicker ice sheet. The long response time of the thermodynamics means that the thermodynamics cannot play a crucial role during transition from a glacial to a deglacial period which occur typically within several thousands of years. The mass balance height feedback has an important function in the buildup of the ice sheet after a warm period like the Eemian. Without isostatic bedrock compensation the ablation will remain very high in some marginal parts, yielding a considerably smaller ice sheet volume for the last glacial period.