Aufeis (Proglacial Icing) in the forefield of a land-terminating outlet glacier in West Greenland – multi-annual and seasonal variability and drivers

In this contribution, we share observations of a braided river plain adjacent to the little ice age moraine of a land-terminating outlet glacier in West Greenland at around 71°N. During three visits in spring (2023 - 2025), we document a plain of refrozen water. We report on the extent, genesis and decay of the aufeis plain and hypothesize on drivers building it. Time-lapse and high-resolution satellite imagery allow us to assign the build-up of the aufeis during core winter until spring and the decay throughout the melting season. We find that long after the disappearance of the snow cover at the adjacent glacier and ice-free environment, the aufeis still is in place. Using multispectral satellite imagery (Sentinel-2) we derive a time series of aufeis extent ranging from virtually no coverage to almost 0.5 km² for the period 2016-2025, using a random forest classification. DEM differences derived from photogrammetric acquisitions using UAVs enable us to estimate ice volumes between 49x10³ (April 2025) and 110x10³ m³ (April 2024), respectively. To understand atmospheric conditions for meltwater generation, we use automated weather station data near the aufeis plain. As another reason for ice formation, we discuss potential water sources related to groundwater aquifers in porous ground moraine material. Finally, bias-corrected CARRA model output was applied to reconstruct meteorological conditions relevant for aufeis formation. Based on a lagged correlation approach, we find statistically significant (p = 0.05) correlations between cumulative positive air temperature departures and aufeis extent summing up approx. 7 years before the respective icing occurrence. While simplified, we discuss a possible long-term relation between icing extent and meltwater generation.