Forms, response times and variability of relative sea-level curves, glaciated North America

Relative sea level curves from glaciated North America reveal coherent spat ial patterns of response times. In the Laurentide Ice Sheet area, curve hal f-lives range from 1.2-1.4 ka at the uplift centre to 1.7-2 ka in a ridge o f high values inboard of the glacial limit. Half-lives decline from this ri dge to less than 1 ka along the margin. In the Innuitian Ice Sheet area, ha lf-lives are about 2 ka at the uplift centre and decline to less than 1 ka at the margin. The central Laurentide response times are about half those o f central Fennoscandia. This accords with the theoretical expectation that central response times are inversely proportional to ice sheet radius for i ce loads large enough that rebound at the centre is insensitive to lithosph eric thickness. The Innuitian central response time indicates that rebound at the centre of this ice sheet, which is much smaller than the Fennoscandi an Ice Sheet, remains sensitive to lithospheric thickness. Radial gradients in response times reflect the increasing influence of the lithosphere at s ites increasingly closer to the margin. Along this gradient, rebound progre sses as though at the centres of smaller and smaller ice sheets. That is, t he effective spatial scale of the ice load decreases toward the margin. Nea r the glacial limit, postglacial isostatic adjustment is complicated by for ebulge migration and collapse. This is seen most strongly in the relative s ea level record of Atlantic Canada, which has subsided during the Holocene more than 20 m more than the adjacent American seaboard. The relative sea l evel history of some areas, notably the St. Lawrence Estuary, is complicate d by tectonic processes. (C) 2000 Elsevier Science B.V. All rights reserved .