High spatio-temporal velocity variations driven by water input at a Greenlandic tidewater glacier

Abstract

Ice flow controls the ice discharge at tidewater outlet glaciers and is, together with frontal ablation, a key process driving the mass loss of the Greenland ice sheet. While annual glacier velocity variations of tidewater glaciers are well studied using satellite-derived data, research on small-scale, short-term speed variations, ranging from sub-diurnal to multi-day scales, remains limited. We deployed a terrestrial radar interferometer, operating at a 1-min sampling interval (30 min resolution after processing) and a spatial resolution of a few meters, to investigate small-scale ice flow variations at the terminus of Eqalorutsit Kangilliit Sermiat, a tidewater outlet glacier in South Greenland. We observed clear diurnal and multi-day ice flow speed variations and link these to a high ice flow sensitivity to additional freshwater input to the glacier system. This water originates from different sources, such as enhanced surface melt during warm periods or sudden drainage events from subglacial or ice-marginal lakes. The amplitudes of diurnal velocity fluctuations remain remarkably consistent throughout the 6 km long terminus area, but their spatial evolution shows clear variability. Spatio-temporal analysis of velocity map time-series revealed a general downstream propagation of diurnal velocity variations. However, on days characterized by particularly high ice flow speeds, these variations start at the terminus propagating upstream in a distinct block-wise pattern, connected to major rifts in the terminus area. We further conclude that the ice flow remains sensitive and reacts fast to short-term surplus water input, despite having established an efficient drainage system towards the end of the melt season.