Quantifying glacier melt enhancement due to dust deposition during the 2022 melt season : Tungnaárjökull glacier, South Iceland

Clean snow has the highest albedo of any natural surface, making snow-covered glaciers an important component of the Earth´s energy balance. However, the presence of light absorbing impurities such as mineral dust on glacier surfaces alters their reflective properties leading to a reduction in albedo, consequently increasing absorption of incoming solar radiation which further impacts the glacier surface mass balance (SMB). Icelandic glaciers portray a high annual and inter-annual variability in SMB due to climate variability but deposition of mineral dust originating from glaciofluvial dust hotspots can have large impacts on summer ablation. The frequency of dust storms and deposition is then controlled by high velocity winds and prolonged dry periods. Additionally, Icelandic mineral dust contains high amount of iron and iron oxides which makes it extremely light absorbing. An extensive dust event occurred over the southwest outlets of Vatnajökull ice cap during early July of 2022 causing surface darkening. To investigate the impact of the dust event on the melt season SMB, this study used automatic weather station (AWS) data from three different sites on Tungnaárjökull glacier, a SW-outlet of Vatnajökull ice cap. Daily melt was estimated with a simple snow-melt model and AWS data. To quantify the overall impact of dust on the melt rates, albedo from 2015 melt season for the three AWS sites was used to simulate the surface albedo for a dust-free surface during the 2022 melt season. Essentially, the dust event caused melt enhancement of almost 1.5 m water equivalent (mwe) above 1000 m elevation. As Icelandic glaciers exhibit large spatial variations over the melt season, the SMB sensitivity to dust deposition varied with elevation, being strongest at the uppermost site. Additionally, the sensitivity to timing of dust event were investigated which demonstrated that earlier occurrence increases the melt while later occurrence reduces the melt, compared to the July event. The results of this study reveal the impact of positive radiative forcing on SMB of Tung