Morphology and distribution of lakes under the Laurentide Ice Sheet: implications for ice flow dynamics

This study examines the distribution and morphology of lakes under the Laurentide Ice Sheet (LIS) to investigate relationships with ice flow velocity, bedrock and basal thermal regime. Palaeo‐ice streams and lobes were important components of the LIS, and properties of lakes in those regions are quantified at high resolution. Lake polygon shapefiles obtained from the HydroLAKES database contain data including water depth, volume and elevation. ArcGIS Pro is used to measure lake area, length, width, elongation, orientation, parallel conformity, density and packing. Approximately 982 282 natural lakes were identified in the region of North America covered by the maximum extent of the LIS during the Last Glacial Maximum. Density of lakes is highest in terrestrial regions surrounding Hudson Bay, and lake density decreases closer to the ice‐sheet margin. Packing shows similar patterns to density with the exceptions of regions covered by remnants of proglacial lakes and non‐glacial lakes. Close examination of density and packing under palaeo‐ice streams and lobes shows statistically significant differences, with greater lake density and packing under palaeo‐ice streams than lobes. Bedrock substrate also plays a key role in lake density and packing, with higher lake density under palaeo‐ice streams flowing over the Canadian Shield compared with density and packing of lakes under palaeo‐ice streams flowing on sedimentary bedrock. Lakes under palaeo‐ice streams have higher parallel conformity than lobes, with orientation in both following ice flow paths. Elongation ratios of lakes under palaeo‐ice streams and lobes are similar. Regions with high lake density are associated with intense ice scouring on the Canadian Shield, while regions with low lake density on sedimentary bedrock suggest a transition from initially high erosion of soft‐bedded terrain followed by depositional processes dominating. High parallel conformity of lakes under palaeo‐ice streams provides evidence for fast ice flow, similar to the presence of mega‐scale glacial lineations. Quantifying lake morphology and distribution under the LIS provides a useful proxy for ice‐sheet dynamics and may help better understand conditions under modern ice sheets, especially in regions of fast ice flow.