Geometric and surface energy balance change affecting Kårsaglaciären, northern Sweden, over the past century

Glacier mass balance depends upon the dynamic change of glacier geometry. Despite this effect being recognised as important, few modelling studies have addressed and quantified it specifically. This study presents a 99 year reconstruction and mass balance response analysis of Kårsaglaciären, a small (0.89 km2) mountain glacier located in Arctic Sweden, using a number of techniques in order to overcome this limitation. A geodetic approach was used to assess changing mass balance over time. Data were derived from topographic maps and contemporary field surveys. These data were used to interpolate a number of DEMs and full 3D reconstructions were derived, providing information on spatial change for the period 1909-2010. A long term trend of negative mass balance was identified. The glacier retreated 1292 m, thinned by 0.35 m w.e. yr-1 and reduced in volume by 1.33 km3 yr-1. The 3D reconstructions provided the input for a user friendly, simple distributed surface energy balance model, aimed at facilitating the assessment of the effect of geometry change on mass balance - designed specifically for this study and made available to other researchers online (https://github.com/Chris35Wills/ SEB_model_java_files). Using the reference balance approach, it was possible to assess change in mass balance over time both with and without dynamic surface adjustment, allowing disentanglement of these effects with climate. Geometry change on an annual basis had little effect on glacier mass balance response to climate but has a significant dampening effect for the period 1926-1943. These results provide evidence of Kårsaglaciären showing a strong pattern of retreat throughout the 20th and early 21st century. From these analyses it is apparent that the effects of glacier geometry on mass balance response are not simply linked by time. Future mass balance studies should consider changes in glacier geometry for accurate assessments of glacier response to climate.