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Abstract:
A change from a low to high friction bed under the North American Ice Complex through the removal of pre-glacial regolith has been hypothesized to play a critical role in the mid-Pleistocene transition from 41 to 100 kyr glaciations. However, this regolith hypothesis requires constraint on pre-glacial regolith cover and topography, mechanistic constraints on what amount of regolith can be removed, and complete process coupling to infer the net effect from topography and sediment changes. This landscape evolution has not yet been simulated for a realistic, 3D North American ice sheet fully considering basal processes (e.g. sedimentary, basal hydrology, and the solid earth response to changing sediment and bedrock load). Constraints of the pre-glacial bed are sparse and the bounds are wide.What constraint does the present day sediment distribution offer and how do topography and sediment change influence glacial cycles? Using varied pre-glacial topographies, sediment thicknesses, and fully coupled climate, ice, sediment and subglacial hydrology model parameterizations, we show the constraint on mean pre-glaciation sediment thickness provided by the present day surface sediment distribution and regional estimates of bedrock erosion. More broadly, we find that this landscape evolution has a strong influence on the strength and duration of early Pleistocene glaciations. The ice, climate, and sediment processes encapsulated in this fully coupled Earth systems model capture the evolution of the Pleistocene North American glacial system: the 41 to 100 kyr glacial cycles transition, early Pleistocene extent, sea level change, last deglacial margins, and broad present-day sediment distribution within uncertainty.
