Accelerating growth of Sermilik Delta, Greenland (1987–2022), driven by increasing runoff

The Greenland ice sheet (GrIS) produces ~8% of the global suspended sediment delivered to the oceans and is the only Arctic region where deltas are advancing. However, understanding of the dynamics of sediment transfer from source-to-sink and the impact of variations in climate and ice sheet processes on sediment yields are uncertain. Here, we investigate controls governing the annual evolution of a proglacial fjord-head delta (Sermilik Delta) located on the southwest coast of Greenland from satellite-derived shorelines and modelled tides (1987–2022). Our results reveal delta progradation of ~26 km² from 1987 to 2022 (0.78 km² year⁻¹) with an accelerating trend controlled by meltwater runoff, including increases in the annual total and frequency of extreme events. The lack of correlation between delta growth and ice velocity, with the latter decreasing over the study period, indicates a readily accessible store of subglacial and proglacial sediment that meltwater can tap into. Expansion of the proglacial zone, which is inundated during high runoff providing a well-connected source of sediment, might explain the strengthened relationship between runoff and delta growth since 2010. We highlight the importance of tides on the morphology of proglacial deltas during low runoff, and the potential of using tidal model data to remove the tidal signal and isolate real changes in delta area.