Annual and inter-annual variability and trends of albedo of Icelandic glaciers

During the melt season, absorbed solar energy, modulated at the surface predominantly by albedo, is one of the main governing factors controlling surface-melt variability for glaciers in Iceland. Using MODIS satellite-derived daily surface albedo, a gap-filled temporally continuous albedo product is derived for the melt season (May to August (MJJA)) for the period 2000-2019. The albedo data are thoroughly validated against available in situ observations from 20 glacier automatic weather stations for the period 2000-2018. The results show that spatio-temporal patterns for the melt season have generally high annual and inter-annual variability for Icelandic glaciers, ranging from high fresh-snow albedo of about 85 %-90 % in spring to 5 %-10 % in the impurity-rich bare-ice area during the peak melt season. The analysis shows that the volcanic eruptions in 2010 and 2011 had significant impact on albedo and also had a residual effect in the following years. Furthermore, airborne dust, from unstable sandy surfaces close to the glaciers, is shown to enhance radiative forcing and decrease albedo. A significant positive albedo trend is observed for northern Vatnajokull while other glaciers have non-significant trends for the study period. The results indicate that the high variability in albedo for Icelandic glaciers is driven by climatology, i.e. snow metamorphosis, tephra fallout during volcanic eruptions and their residual effects in the post-eruption years, and dust loading from widespread unstable sandy surfaces outside the glaciers. This illustrates the challenges in albedo parameterization for glacier surface-melt modelling for Icelandic glaciers as albedo development is driven by various complex phenomena, which may not be correctly captured in conventional energy-balance models.

Automated summary

The study focuses on the impact of solar energy absorption and albedo on surface-melt variability for Icelandic glaciers during the melt season. It finds that the albedo for Icelandic glaciers exhibits high annual and inter-annual variability, influenced by climatology, volcanic eruptions, and airborne dust. The results highlight the challenges in accurately parameterizing albedo for glacier surface-melt modeling due to the complex phenomena involved.