Comparison of four calving laws to model Greenland outlet glaciers

Abstract

Calving is an important mechanism that controls the dynamics of marine terminating glaciers of Greenland. Iceberg calving at the terminus affects the entire stress regime of outlet glaciers, which may lead to further retreat and ice flow acceleration. It is therefore critical to accurately parameterize calving in ice sheet models in order to improve the projections of ice sheet change over the coming decades and reduce the uncertainty in their contribution to sea-level rise. Several calving laws have been proposed, but most of them have been applied only to a specific region and have not been tested on other glaciers, while some others have only been implemented in 1-D flowline or vertical flowband models. Here, we test and compare several calving laws recently proposed in the literature using the Ice Sheet System Model (ISSM). We test these calving laws on nine tidewater glaciers of Greenland. We compare the modeled ice front evolution to the observed retreat from Landsat data collected over the past 10 years, and assess which calving law has better predictive abilities for each glacier. Overall, the von Mises tensile stress calving law is more satisfactory than other laws for simulating observed ice front retreat, but new parameterizations that better capture the different modes of calving should be developed. Although the final positions of ice fronts are different for forecast simulations with different calving laws, our results confirm that ice front retreat highly depends on bed topography, irrespective of the calving law employed. This study also confirms that calving dynamics needs to be 3-D or in plan view in ice sheet models to account for complex bed topography and narrow fjords along the coast of Greenland.