Investigating the drivers of Helheim Glacier’s variability from 2007 to 2020

Abstract:

At least half of today’s mass loss of the Greenland ice sheet is due to the retreat of tidewater glaciers. For example, Helheim Glacier, in southwest Greenland, has been changing dramatically during the previous decade. While there is broad agreement that the retreat and acceleration of these marine terminating glaciers has been triggered by the intrusion of warmer currents in the fjords, other processes such as changes in basal conditions, surface mass balance or calving dynamics may have also played important roles in controlling the retreat of these glaciers. However, our understanding of these processes and their contributions to the retreat and acceleration of the glaciers remains still limited. The individual contributions of these processes have not been quantified, which makes it difficult to determine which of these processes should be included in ice sheet models to correctly capture the present and future retreat and associated mass loss of the ice sheet. Here, we simulate the dynamics of Helheim Glacier, Greenland, from 2007 to 2020 using the Ice Sheet System Model (ISSM) to investigate the model response to changes in external forcings and boundary conditions, such as basal friction, surface mass balance, ice-ocean interaction at the calving front. The relative importance of each external forcing mechanism to the model is quantified within a series of numerical experiments, where each component is switched off and the resulting solution is compared with observations. We evaluate the ability of the model to match surface speed and surface height observations collected during the simulation period. Preliminary results suggest that Helheim’s dynamics is relatively insensitive to the choice of friction law or the surface mass balance, but that the position of the calving front and changes in basal sliding conditions are critical to explain the high variability of Helheim’s surface speed. This study, as a result, can be used as a guide for model development of similar glaciers.