Abstract

The network of lake-level gauges in place for Lake Winnipeg, Lake Winnipegosis, Lake Manitoba, and Lake of the Woods presents an opportunity to study the contemporary pattern of postglacial rebound in a North American continental-interior region. We used a regional trend-surface model based on mean winter-season differences of lake level between pairs of gauges to extract the postglacial rebound signature recorded in the lake-gauge data. The results from a best-fitting planar model indicate that tilting is up to the northeast with a bearing of N(42.7 ± 11.8)°E and a rate of (10.7 ± 2.2) × 10−9 rad ṁ yr−1. In spite of the fact that both the ICE-3G and ICE-4G load models are derived from the inversion of relative sea-level histories obtained from marine coastal sites, the pattern of rebound that we computed from these two ice models for this continental-interior region agrees reasonably well with the pattern derived from the lake-gauge data. Rates computed from an ICE-3G load are in close agreement with those computed from the lake gauges, whereas rates derived from ICE-4G are 50% too slow. When the planar pattern of postglacial rebound derived from the lake gauges in southern Manitoba and Lake of the Woods is linked to the lake-gauge–derived pattern of rebound over the Great Lakes region, the two-region pattern suggests influential source regions of rebound that include southern and southwestern Hudson Bay as well as more local sources in western Ontario. It is possible that the spatial arrangement of ice domes predicted in the multidomed paleotopography of ICE-4G could explain the two-region pattern of rebound if more ice were added to Ontario in the model, or if Earth structure assumptions could be modified, or both.

As postglacial tilting continues to shift the region's lakes to the southwest, there is an increased risk of flooding and wave erosion along the south shores over the long term. In addition, postglacial tilting deforms the datums to which the lake-level gauges are referenced. Thus, where and how the levels of these lakes are measured is an important operational issue. These factors present challenges to water-resource managers who are responsible for monitoring the levels and controlling the outflows of these lakes.

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