Collaborative Research: What Controls Calving? A Greenland-wide Test of Terminus Change Mechanisms

Retreat of the leading edge of marine-terminating glaciers is often associated with ice flow acceleration, increases in iceberg calving rates and discharge to the sea, and glacier thinning. The associated ice mass loss is responsible for approximately half the contribution of the Greenland Ice Sheet to sea level rise thus far this century. For the remainder of the century and beyond, gaps in our understanding of iceberg calving and glacier retreat result in large uncertainties in predictions of mass loss and consequent sea level rise. This collaborative project is designed to reveal the factors controlling terminus retreat and iceberg calving in the diverse settings of Greenland's marine terminating glaciers. The project contributes to STEM workforce development by providing support to two early-career scientists from EPSCoR states, undergraduate student participation at both institutions, and for training of a graduate student. The principal investigators will continue their active outreach, including museum and classroom visits in the rural settings around their universities, presentations to non-technical groups, and media features. This project will substantially improve our understanding of marine terminating glacier dynamics via the analysis of recently-available observational datasets. Through these data, the project will evaluate the performance of terminus parameterizations used in numerical ice sheet models, known as "calving laws." Application at 49 diverse marine-terminating glaciers around Greenland (nearly a quarter of the ice sheet total) ensures that project results will be representative. Calving laws applied to conditions at and near glacier termini will predict terminus locations. Predictions will be compared to terminus positions observed in satellite and time-lapse images to identify model misfits. This calibration and validation analysis will reveal when and where specific calving laws reliably reproduce terminus positions and calving rates. Furthermore, extensions of this approach will (1) yield insight into the impact of crevasse water storage on iceberg calving, (2) guide the inclusion of submarine melting to improve prediction by calving laws, and (3) quantify the critical timescales over which glacier properties must be characterized for the prediction of calving rates and terminus positions.