GIS-analyses of ice-sheet erosional impacts on the exposed shield of Baffin Island, eastern Canadian Arctic

Abstract

The erosional impacts of former ice sheets on the low-relief bedrock surfaces of Northern Hemisphere shields are not well understood. This paper assesses the variable impacts of glacial erosion on a part of Baffin Island, eastern Canadian Arctic, between 68 and 72°N and 66 and 80°W. This tilted shield block has been covered repeatedly by the Laurentide Ice Sheet during the late Cenozoic. The impact of ice-sheet erosion is examined by GIS-analyses using two geomorphic parameters: lake density and terrain ruggedness. The resultant patterns generally conform to published data from other remote sensing studies, geological observations, cosmogenic exposure ages and the distribution of the Chemical Index of Alteration for tills. Lake density and terrain ruggedness are thereby demonstrated to be useful quantitative indicators of variable ice-sheet erosional impacts across Baffin Island. Ice-sheet erosion was most effective in the lower western parts of the lowlands, in a west-east oriented band at around 350-400 m a.s.l. and in fjord onset zones in the uplifted eastern region. Above the 350-400 m a.s.l band and between the fjord onset zones, ice-sheet erosion was not sufficient to create extensive ice-roughened or streamlined bedrock surfaces. The exception where lake density and terrain ruggedness indicate that ice sheet erosion had a scouring effect all across the study area was in an area from Foxe Basin to Home Bay that does not exceed elevations of 400 m a.s.l.. These morphological contrasts link to former ice sheet basal thermal regimes through the Pleistocene. The zone of low glacial erosion surrounding the cold-based Barnes Ice Cap probably represents its greater extent during successive Pleistocene cold stages. Inter-fjord plateaus with few ice sheet bedforms remained cold-based throughout multiple Pleistocene glaciations. In contrast, zones of high lake density and high terrain ruggedness are a result of the repeated development of fast-flowing, erosive ice in warm-based zones beneath the Laurentide Ice Sheet. These zones are linked to greater ice thickness over western lowland Baffin Island. Adjacent lowland surfaces with similar elevations, however, of non-eroded, weakly eroded, and ice-scoured shield bedrock indicate that even in areas of high lake density and terrain ruggedness the total depths of ice-sheet erosion did not exceed 50 m.