NSFGEO-NERC: Collaborative Research: How important are sea-level feedbacks in stabilizing marine-based ice streams?

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Among the largest uncertainties in projections of 21st century sea-level rise is whether and how the Greenland and Antarctic Ice Sheets may collapse as global temperatures increase. One aspect of this uncertainty concerns how the solid Earth responds to melting ice in the form of post-glacial rebound, that is, uplift of crust after the weight of the ice has been removed. This project will examine the behavior of the Earth beneath the ice sheet that covered northwest Scotland during the Last Glacial Maximum, 20,000 years ago. As the earth warmed following the Last Glacial Maximum the ice sheet shrank and around 17,000 years ago a portion of the ice sheet over northwest Scotland experienced a “collapse” or period of fast retreat. The research will use records of past sea levels to document the behavior of the Earth beneath the front of this retreating ice sheet to determine if it rebounded (uplifted) fast enough to help stabilize the retreating ice sheet. There will also be numerical experiments to recreate the behavior of the Earth and ice sheet during this time period and compare these model experiments with measured records of past sea level changes across Scotland. These comparisons will permit new insights into the behavior of retreating ice sheets and provide better constraints on the history and size of the ice sheet that once covered northwest Scotland. The project will conduct a three-week in-residence summer camp for students from high schools with large minority populations to introduce them to the varied dimensions of Earth Science. The purpose of this research is to investigate the importance of sea-level feedbacks in stabilizing marine-based ice sheets during their retreat. The proposed investigation will combine new late Pleistocene/Holocene relative sea-level constraints to be collected from raised shorelines, existing offshore marine cores, and isolation basins from across northwestern Scotland, to refine the glacial isostatic adjustment models for the British Isles. The proposal will also investigate sea-level feedbacks at a more local level and at the scale of the Late Pleistocene ice stream that once flowed through the Minch of northwestern Scotland using a more specialized ice-sheet model. This model, coupled with results from an improved “global” scale glacial isostatic adjustment model for the British Isles, will be used to understand the sensitivity of the former Minch ice stream to more local variables (e.g. mantle rheology, lithospheric thickness, ice sheet geometry, etc.). Three hypotheses will be tested: 1.) Sea-level feedback did not provide a stabilizing influence for the Minch Ice Stream during its retreat following the Last Glacial Maximum; 2.) along indented ice-sheet margins, sea-level feedbacks are governed not by the local ice front but by regional isostatic adjustment; and 3.) the influence of sea-level feedback in stabilizing marine ice streams is a function of the rheology of the Earth beneath it.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.