Loss of accumulation zone exposes dark ice and drives increased ablation at Weißseespitze, Austria

Abstract

In recent years, firn and summer snow cover have decreased on Alpine glaciers, exposing larger areas of ice at higher elevations. This reduces albedo and leads to increased melt. To understand mass loss in former accumulation areas under conditions of rapid glacier recession, it is important to constrain the possible range of ice albedo in newly firn-free regions, the duration of ice exposure, and the albedo-ablation relationship. We combine data from an on-ice weather station (3492 ma.s.l.), ablation stakes, and remote-sensing-derived albedo to provide an overview of albedo and ablation in the summit region of Weißseespitze, the high-point of Gepatschferner (Austria), from 2018 to 2024. Before 2022, low albedo (<0.4) occurred on 3-8 dyr-1. In 2022, 37 d of low albedo values were recorded by the weather station, and albedo dropped below previously observed minima of around 0.30 to values similar to those of the surrounding rock. Albedo remained very low in 2023 and 2024. Ice ablation at the stakes generally increased with the duration of ice exposure. Losses of up to 1.7 mmw.e. were recorded in high-melt years. Sensitivity experiments indicate that a 5 d period of very low albedo conditions (<0.20) results in about 30 % more modeled surface melt if it occurs in late July compared to early September, highlighting temporal variability in the impact of ice exposure. The unique Weißseespitze dataset provides a starting point for further studies linking causes and effects of albedo changes in former accumulation zones.