Tracking Past Ice Sheets with North American River Drainage Basin Captures Induced by Glacial Isostatic Adjustment

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This team of investigators will build a framework to test past ice sheet geometries using shifts in river drainage basin boundaries induced by glacial isostatic adjustment, as recorded by sediment provenance. They will simulate topographic change over North America using a state-of-the-art gravitationally self-consistent glacial isostatic adjustment model. They will perform calculations using two differing potential ice sheet loading histories over the last ice age. Using these predictions, they will calculate how drainage basin boundaries changed over the last ice age (120-0 ka) for major North American river systems. To model sediment provenance variations, they will superimpose a North American bedrock age map onto the predicted maps of drainage basin shifts due to glacial isostatic adjustment. Finally, they can predict how glacial isostatic adjustment shifts the age distribution of detrital grains (sediment provenance) drained into major North American Rivers over the ice age. Ultimately these predictions can be compared to existing and future sediment provenance records to identify likely past ice sheet size and geometry. This project will support an early-career principal investigator from an underrepresented group. She will develop innovative teaching tools for making legible the roots of geoscience culture in scientific racism and imperialism. These tools will be incorporated into courses taught at UC Santa Cruz. The project will support a PhD student and their enrollment in the Science & Justice Training Program. Here the student will learn how science is implicated in the co-production of social inequities. The principal investigator will participate in outreach to middle school students in the Alaska Native Science & Engineering Program and will mentor summer undergraduate students through the UC-HBCU Initiative.This interdisciplinary work, spanning geophysics, geomorphology, and sedimentology, will improve our understanding of past continental ice sheets and associated climate change. The research will expand the current toolset for inferring past ice sheets, setting a foundation for an unprecedented, novel method aimed at ice-sheet reconstruction over multiple glacial cycles. By robustly testing the influence of glacial isostatic adjustment on drainage basin shifts recorded in sediment provenance, the team will demonstrate the plausibility of drainage basin evolution as a potential new constraint on past ice sheets. This finding would enable ice-age researchers to transcend challenges imposed by the erosional nature of ice sheets, which destroy geologic evidence of past ice margins as they advance. Instead, it should be possible to infer the geographic extent and thickness of past ice sheets deeper in time, over many glacial cycles, and this approach is limited only by the age of sedimentary deposits, which can span millions of years. Furthermore, quantifying the influence of glacial isostatic adjustment on river drainage basins will improve our understanding of landscape evolution on ice age timescales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.