Klimarekonstruktion aus dem Eis grosser Eisschilde
by K. HUTTER, R. GREVE, R. CALOV
Specimens from ice cores of polar ice sheets (Greenland, Antarctica) allow determination of the past climate of the Earth by determination of the isotopic composition of the water molecules and examination of the air trapped in included pores. This requires assigning simultaneously the age to an ice specimen taken from a certain depth ("dating"), which can be achieved either by several stratigraphic methods or by computer simulations of the creeping motion of the ice with a suitable model.
The motion of the ice in polar ice sheets is similar to the spreading of honey on the breakfast plate. Rheologically, the ice is regarded as a very viscous, thermo-mechanically coupled power-law fluid which shows a gravitationally induced creeping flow. At the free surface this ice mass is subject to the climatic forcing which encompasses temperature variations of the atmosphere, accumulation of snow due to precipitation and ablation of ice due to melting. Because of the ice load, the solid earth beneath the ice deforms as well, but it equally serves as a heat source via the geothermal heat flux. This complex initial-boundary-value problem is discussed together with its difficulties. Solutions are presented for paleoclimatic reconstructions of the Greenland ice sheet along with the resulting datings for the central-Greenlandic ice cores GRIP and GISP2.
