Deglaciation of the Northern Hemisphere at the onset of the Eemian and HoloceneR. GREVE, K.-H. WYRWOLL and A. EISENHAUER AbstractHigh resolution (TIMS) U-series dating of sea level events obtained from coral reef complexes has suggested that the global deglaciation from the Saale (penultimate) glacial to the Eem interglacial (marine delta-O18 stages 6/5) may have occured earlier in relation to Milankovitch insolation forcing than that from the Wisconsin glacial to the Holocene interglacial (marine delta-O18 stages 2/1). However, the interpretation of these data have been problematic because of the possibility of isotope exchange. In order to investigate whether these different lead/lag relations between Milankovitch forcing and ice volume are feasible from the point of view of large-scale ice-sheet dynamics and thermodynamics, the 3-d polythermal ice-sheet model SICOPOLIS is applied to the entire northern hemisphere (which gives the major contribution to global ice volume changes due to the relative stability of the Antarctic ice sheet), and simulations through the two last climatic cycles are conducted. The simulations cover the time interval from 250 ka BP until today and are driven by surface-temperature reconstructions of deep ice cores (GRIP, Vostok) and simple parameterizations for the change of precipitation with time. Discussion of the results is focussed on the Saale/Eem and the Wisconsin/Holocene transitions. The amount and rate of deglaciation are in good agreement with the SPECMAP record for both cases, and the evidence of the data for an early start of the Eem interglacial is supported. Annals of Glaciology, 28, 1-8 (1999). |
|
|