The importance of calving in ice sheet models: A sensitivity study of ice front retreat in the Amundsen Sea Embayment

Calving is a key process in the dynamics of marine-terminating glaciers with large ice shelves, such as those in West Antarctica. However, this process is currently not included in most predictive models, due to its difficulty to implement in a general form which can reliably reproduce rates of calving over a range of scenarios. We set out to investigate how important it is to develop such representation of calving for future modelling.

In this study, we quantify the sensitivity of modelled future mass loss to ice front retreat in the Amundsen Sea Embayment, including Pine Island and Thwaites Glaciers. We find that prescribing constant frontal retreat rates from 0.1 to 1 km a_­­^-1 progressively increases the contribution to sea level rise when compared to experiments with a fixed ice front. The result is up to 80% more loss of ice by 2100, and more than triple the ice loss in projections beyond 2200 with the higher rates of retreat. The spatial pattern of ice loss is non-uniformly distributed, with some regions thinning and others thickening as an initial response to the calving front retreat. We identify specific thresholds in the geometry of the system, which have clear effects on the ice flow and are reached at different times depending on the retreat rate.

We compare variability in the range of our results using different retreat rates to that in the range of ISMIP6 ocean forcing products, as ocean-induced melt is known to be a major factor in determining the future evolution of the Antarctic ice sheet. We find that the variability due to these two factors is initially similar, and that variability due to ice front retreat becomes comparatively greater over time. Our results demonstrate the high importance of accurately representing calving processes in models, showing that they are at least as important as ocean forcing and deserve a similar amount of attention in future model development work.