Greenland’s Jakobshavn Glacier (locally known as Sermeq Kujalleq) is one of the fastest-moving glaciers in the world and a major contributor to sea-level rise. We have a new study looking at the ice-sheet area, or catchment, that Jakobshavn drains. One of the approaches for assessing the mass balance, or health, of Jakobshavn is the input-output method. This method differences iceberg discharge into the ocean across the grounding line from net snow accumulation within its upstream catchment. This means you need a pretty good idea of Jakobshavn’s catchment area. But, today’s currently available delineations of Jakobshavn’s catchment area vary by ±12%. This uncertainty in catchment area translates into an uncertainty in area-integrated net snow accumulation.
Glacier catchments are not constant through time. For this study, we looked at how Jakobshavn’s catchment area might evolve in the future. We used an ensemble of future ice flow simulations created for the Ice Sheet Model Inter-comparison Project (ISMIP6) to delineate Jakobshavn’s catchment under different climate scenarios to the year 2100. The ensemble suggests that Jakobshavn’s catchment could expand by 3–9%, depending on the intensity of ocean and atmospheric warming of a given climate scenario. These changes in Jakobshavn’s catchment appear to trigger a phenomenon called “dynamic piracy,” whereby Jakobshavn is essentially stealing ice from its neighboring glaciers, redirecting it into its own flow toward the ocean.
Generally, however, the ensemble of models has some challenges reproducing recently observed reorientations in inland ice flow. The models are generally less sensitive to climate change, producing less acceleration than actually observed. All but one of the ensemble members fail to reproduce recent accelerations in ice flow observed about 100 km inland from Jakobshavn’s terminus. We interpret this as suggesting that the current ensemble of models likely underestimates future reorientations in deep inland ice flow. Simply put, they may not fully capture how rapidly the ice sheet’s catchments are reorganizing themselves under future climate change.
Our analysis of the ISMIP ensemble reminds us that big outlet glaciers are not just passive responders to climate change; they actively reshape their catchments in ways that ripple through the ice sheet. So, if we want accurate glacier-scale input-output assessments, then we need to have accurate glacier-scale catchments, both today and in the future. This highlights the importance of improving our delineation of ice-sheet catchments using both observational methods and ice flow models. This also means continually improving the ice flow models used to predict the future form and flow of Earth’s ice sheets.
Løkkegaard A., W. Colgan, A. Aschwanden and S.A. Khan. 2024. Recent and future variability of the ice-sheet catchment of Sermeq Kujalleq (Jakobshavn Isbræ), Greenland. Journal of Glaciology. 1-15. https://doi.org/10.1017/jog.2024.73
