Delta progradation in Greenland driven by increasing glacial mass loss

Climate changes are pronounced in Arctic regions and increase the vulnerability of the Arctic coastal zone. For example, increases in melt of the Greenland Ice Sheet (GrIS) and reductions in sea ice and permafrost distribution are likely to alter coastal morphodynamics. The deltas of Greenland are largely unaffected by human activity, but increased freshwater runoff and sediment fluxes may grow deltas while increased wave activity in ice-free periods could reduce their size —with the net impact being unclear until now. Here we show that southwestern Greenland deltas were largely stable from the 1940s-1980s, but prograded in a warming Arctic from the 1980s-2010s. Our results are based on the areal changes of 121 deltas since the 1940s, assessed using newly discovered aerial photos and remotely sensed imagery. We find that delta progradation was driven by high freshwater runoff from the GrIS when coinciding with periods of open-water. Progradation was controlled by the initial environmental conditions (i.e. absolute values for thawing degree days, freshwater runoff, and sea ice in 1980s) rather than local changes in these conditions from the 1980s to 2010s at each delta. This is in contrast to a dominantly eroding trend of Arctic sedimentary coasts along the coastal plains of Alaska, Siberia and Western Canada and to the spatially variable patterns of erosion and accretion along the large deltas of the major rivers in the Arctic. This work improves the understanding of Arctic coastal evolution in a changing climate, and illuminates impacts on coastal areas of increasing ice mass loss and associated freshwater runoff and lengthening of open-water periods.