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 (Qooqqup Sermia), subject to the same regional climate 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 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 regional climate forcing and fed by the same upstream ice masses, the two termini show contrasting front dynamics in the long- and short-term. We infer extremely low subaqueous melt rates in the lake as one of the main differences between the two environments, likely contributing to the observed contrast in dynamics. 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 separate estimates of frontal ablation through subaqueous melt when included in model simulations of the Greenland Ice Sheet.