Vertical distribution of water within the polythermal Storglaciären, Sweden

Abstract

Knowledge of water content and its distribution in polythermal glaciers is required to model their flow and thermal state. However, observations of water content variations with depth in polythermal glaciers are scarce. Water content can be estimated from radio wave speed because they depend on one another. We obtained continuous profiles of radio wave speed variations with depth from zero‐offset radar profiles collected in boreholes approximately 80 m deep in the upper ablation area of Storglaciären, northern Sweden. These profiles show that the microcrystalline water system in the temperate ice is relatively homogeneous. The overall hydrothermal structure at this location is composed of a 20 m thick upper layer of cold, water‐free ice, underlain by a temperate ice layer whose average water content is 0.6% ± 0.3%. These results are corroborated by surface radar and thermistor measurements, which show that the depth of the cold temperate transition is 21 m and the calculated water content at that transition is 0.6% ± 0.1%. These findings imply that the whole temperate ice layer is from 3 to 4 times softer than the cold ice and, consequently, that realistic ice flow models of polythermal glaciers should include the effect of water content on viscosity.