Cold Surface Layer Dynamics of Storglaciären, Northern Sweden 2009-2019

Abstract: Storglaciären is a sub-Arctic polythermal glacier in northern Sweden. Twenty years' monitoring of thecold surface layer found that it has lost one third of its total volume of cold ice with an average thinningrate of 0.80 ± 0.24 m·a-1 for the period of 1989-2009. This thesis presents the continuous investigationof the thermal structure evolution of Storglaciären using thermistor string measurements and a coupledenergy balance-snowpack model. The thickness dynamics of the cold surface layer is derived from boththe thermistor string measurement (2018-2019) and the simulation results (2009-2018).    The subsurface temperature evolution and the associated cold-temperate transition surface (CTS)dynamics are analyzed at both the thermistor scale and glacier scale. Point study involves installing athermistor string and extrapolating the measured subsurface temperature to the pressure melting pointisotherm depth. The simulated CTS depth changes at the study site was also used for comparison. Glacierscale study aims to simulate the spatial and temporal variations of the thickness of the cold surface layer.Meteorological data was collected from multiple automatic weather stations and the solid precipitationwas estimated from the winter mass balance survey. The model was utilized in the study of the coldsurface layer dynamics for the first time.    Both the point scale and glacier scale study suggest an overall thickening trend of the cold surfacelayer. The thermistor derived CTS depth exhibits a thickening rate of ~0.9 m·a-1 compared to the depthderived from ground penetrating radar survey in 2009. The influence of mass balance, melt andaccumulation are also examined by spatial correlation with CTS depth.