Contrasting dynamics of lake- and marine-terminating glaciers under same climatic conditions

Abstract. In Greenland, mass wasting through frontal ablation occurs not only at the ice-ocean interface but also at the ice-lake intersection. Recent studies have found that lakes cover 10 % of the entire ice sheet margin and stress the importance of understanding frontal dynamics in lacustrine settings. However, relatively little is known about how lake-terminating glaciers compare to marine-terminating glaciers under the same climatic conditions. At a unique study site in South Greenland, a lake and a marine terminus are part of the same glacier system, subject to the same climatic forcings and fed by the same upstream ice masses. In this study, we analyse the drivers of change at both glacier fronts and compare their dynamics with a comprehensive remote sensing dataset supported by climate and ocean model output. Furthermore, during two field campaigns, we collected lake bathymetry data alongside temperature and lake level measurements. We find that despite being subject to the same climatic forcing and fed by the same upstream ice masses, the two termini show contrasting front dynamics in the long- and short-term. We argue that low subaqueous melt rates in the lake are the main driver of these differences. Furthermore, we find lake ice to limit calving activity, similar to an ice mélange at marine-terminating glaciers. A massive disintegration event of more than 3 km of the lake terminus showcases the possibility of rapid mass loss at lake-terminating glaciers in Greenland. Our results stress that lake- and marine-terminating glaciers require different parameterisations when included in model simulations of the Greenland Ice Sheet.