Assessment of the ocean contribution to mass loss of Greenland’s peripheral glaciers – a scale-transitioning approach

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Apart from the large main ice sheet, Greenland is home to a huge number of far smaller peripheral glaciers. Their contribution to the overall mass change of Greenland is greatly exceeding their share of ice mass, and surface area. Since they are mostly located in mountainous terrain along the coast of the island, numerical models of these ice masses need to consider the adequate spatial resolution, which cannot be achieved by ice sheet models. Tidewater glaciers are contributing a particularly large part to the overall mass loss. During 2003 to 2008, the peripheral glaciers contributed 14% to the overall ice mass loss of Greenland. Their contribution to sea level rise is projected to increase in the future, with currently available projections suggesting ice mass losses of the peripheral glaciers of up to 50% during the 21st century under RCP 8.5 forcing. There is strong spatial variation in peripheral glacier mass change, which mirrors a complex combination of forcing mechanisms from both atmosphere and ocean. Nevertheless, none of the currently available models which are capable of calculating regional-scale glacier mass change explicitly includes ocean forcing of frontal ablation processes at the marine-terminating fronts of tidewater glaciers. Except for two models, none even considers any frontal ablation processes at all. Hence, no past, present or future estimates of frontal ablation at Greenland's peripheral tidewater glaciers are available so far.The aim of the project is to produce projections of the future evolution of Greenland's peripheral glaciers during the 21st century, forced by the CMIP6 ensemble, with special attention to tidewater glaciers. We will quantify their freshwater discharge and contribution to sea-level rise. We will extend the Open Global Glacier Model (OGGM) to include ocean forcing in its frontal ablation module. This will be assisted by dedicated downscaling routines for both atmospheric and oceanic boundary conditions. We will evaluate the performance of OGGM with respect to the application of different scales of forcing data to determine if, and to which extent, optimized scale transitioning from the large synoptic scale down to the smaller local scale of the peripheral glaciers is able to increase model performance. The project results will provide an increased understanding of the influence ocean and atmosphere on the evolution of Greenland's peripheral glaciers. We will further provide advice regarding the optimal complexity of modeling strategies regarding regional-scale glacier modeling, particularly of tidewater glaciers.