NORTH AMERICAN DEGLACIATION AND DRAINAGE EVOLUTION

Previous reconstructions of the post-Last Glacial Maximum (LGM) ice sheets and drainage systems of North America have been based on geological data, geophysical modeling of glacial isostatic adjustment (GIA), and/or modeling of ice physics driven by climate. Ongoing efforts to refine ice sheet and meltwater histories are actively integrating these approaches, and there is a need to produce models that better incorporate deglacial drainage constraints. Here we present a data-driven history of North American drainage from the Last Glacial Maximum to the present. This record, compiled from over 200 sources, includes constraints from glacial geologic mapping, fluvial geomorphic evolution, and offshore (chemo-)stratigraphy. We compare these with drainage basins and meltwater discharges computed using four modeled ice sheet histories and their associated GIA-induced sea level changes. We find that the GIA-based ice sheet reconstructions do not produce drainage histories that fit well with available geological data, while ice-physics-based modeling preserves some of the characteristics present in the data. These comparisons provide geographic constraints on ice sheet thickness that can be combined with GIA and ice physics models to generate improved reconstructions of past ice distributions across North America, and therefore the contributions of the North American ice sheet sectors to deglacial sea level rise.