Symposium on glacier beds: the ice-rock interface

Abstract

This paper presents predictions of palaeo-subglacial lakes and their drainage pathways beneath the North American Ice Sheet during the last glaciation. We utilise data on the current topography and seafloor bathymetry, and elevation models of the ice- and ground-surface topography from data-calibrated glaciological modelling to calculate the hydraulic potential surface at the ice-sheets bed. Given that specific ice-surface elevations are only known from modelled outputs, and thus contain significant uncertainty, we utilise many such outputs to examine where on the bed that subglacial lakes are likely to have occurred. Our analysis demonstrates the potential for subglacial lake genesis, particularly beneath the former Cordilleran Ice Sheet; along the suture zone between the Laurentide and Cordilleran ice sheets; in Hudson Bay; in the Great Lake basins and deep trenches of the Canadian Archipelago. During the Last Glacial Maximum we suggest that at least 1000 km3 of meltwater could have been stored subglacially. As the ice-sheet and the bed evolved subglacial lakes repeatedly formed and emptied, particularly in Hudson Bay and the suture zone between the Laurentide and Cordilleran ice sheets where lakes were characteristically broad and shallow (<10 m deep). In contrast, the Cordilleran Ice Sheet was characterised by deep (up to ∼90 m) and persistent lake genesis. Significantly, similar distributions and modes of predicted subglacial lakes are obtained irrespective of the model or model run, which suggests the results are robust. Subglacial meltwater drainage varied between stable networks, typically associated with strong topographic controls, and convoluted networks that underwent considerable dynamism, including repeated meltwater network capture. These lake likelihood predictions could usefully form targets for detailed field and remote investigations and we hypothesise and explore the potential that numerous deposits and spillways previously interpreted as arising from ice-marginal lakes may have emanated from their subglacial cousins.