28 Ice Sheets as Active Agents of Sediment Redistribution in the Earth System

Saturday, 26 July 2003
8:00 AM - 12:00 PM

SPATIO-TEMPORAL PATTERNS OF FENNOSCANDIAN ICE SHEET EROSION

Paper number: 28-2
Program: SYMPOSIA
Time: 8:10 AM – 8:30 AM

Authors

Abstract

Direct geological evidence for erosion beneath the Fennoscandian Ice Sheet (FIS) yields a variability between zero and >30 m per glacial cycle. Morphological evidence and cosmogenic dating confirmation indicate that large regions experienced insignificant glacial erosion despite sustained ice cover. One key factor controlling the pattern of subglacial preservation is topographically induced basal thermal zonation. This spatial variability indicates that the concept of average glacial erosion, though of interest in long-term landscape evolution models, should be applied with caution as it will involve the calculation of average erosion from physical systems (frozen-based versus wet-based) with entirely different modes of functioning. A better understanding of the glaciological mechanisms that control the geological patterns requires that the more specific where and when’s of glacial erosion are addressed.

We here attempt to decipher the first-order and second-order erosion patterns of the FIS, using mapped distributions of bare bedrock (erosional regime) and thick drift covers (depositional regime), in conjunction with time-stratified ice sheet flow patterns, as the primary input data to our qualitative analysis.

Our analysis suggests that the pattern of erosion and deposition can be largely explained by considering the effects of a binary glaciation model. This model entails the existence of a Mountain Ice Sheet (MIS) configuration and a Full Fennoscandian Ice Sheet (FFIS) configuration. MIS configurations were dominant between 2.5 and 0.9 Myr and during initial stages of subsequent glacial cycles. FFIS configurations were dominant only during the last 0.9 Myr. In the west, the erosional and depositional zones of the two configurations roughly coincide. On the other hand, these zones are spatially distanced in the central, southern and eastern parts of the area. Thick till covers occur at the formerly eastern margins of successive MIS, and we note that subsequent FFIS have been unable to completely remobilize this material, presumably because of low ice flow velocities and largely frozen-based conditions in its central parts.