CONSTRAINING THE HIGHEST PROJECTIONS OF FUTURE SEA LEVEL RISE: EVALUATING MODELS OF MARINE ICE CLIFF INSTABILITY AT CRANE GLACIER, ANTARCTICA

Projections of the Antarctic Ice Sheet’s contribution to future sea level rise remain uncertain. While many factors contribute to the spread in ice sheet projections, the largest and most controversial source of uncertainty is the Marine Ice Cliff Instability (MICI), a hypothesized but unobserved process of self-sustaining retreat initiated when ice cliffs reach a critical height and collapse under their own weight. Physical models indicate that glacier geometry and near-terminus velocity determine whether MICI will initiate at a glacier after ice shelf collapse, but models disagree about the exact critical cliff height values required for initiation. In 2002, the Larsen B Ice Shelf (LBIS) rapidly collapsed, offering an opportunity to investigate the potential for MICI initiation in the glaciers it buttressed. Crane Glacier, an LBIS tributary, is referenced in the literature as the only location to display behavior consistent with MICI. Here we assess the configuration of Crane Glacier both preceding and following LBIS collapse to evaluate (1) whether or not Crane likely experienced MICI in the days following LBIS collapse, (2) whether Crane might be a valuable glacier to monitor for potential future MICI activity, and (3) whether observational data at Crane is compatible with the assumptions that underpin MICI models. We analyze data collected via ice penetrating radar, synthetic aperture radar, and satellite altimetry to understand changes in Crane’s dynamics after ice shelf collapse. Preliminary analysis indicates that cliff failure was (and remains) unlikely at Crane, with viscous deformation currently outpacing brittle processes. If correct, MICI would remain unobserved at Earth’s surface, limiting our ability to test parameterizations of ice cliff collapse and leaving persistent uncertainty in the high end of sea-level rise projections.