Evidence towards a thermal lag in the response of Karsaglaciaren, northern Sweden, to climate change

Recent topographical and ground-penetrating radar (GPR) surveys of Karsaglaciaren, which is a small (<1 km(2)) and thin (<56 m) mountain glacier in Arctic Sweden, show that there are small areas of temperate ice in the lowermost part of the glacier. This is curious because we would expect such a small and thin glacier to have a fully cold ablation zone. Specifically, with our analyses of present glacier geometry and thickness and of the prevailing climate, we are unable to explain the presence of temperate ice within the snout of Karsaglaciaren using prevailing models of glacier thermal structure. This leads us to suggest that the presence of temperate ice within Karsaglaciaren is a remnant of a previous polythermal state that existed when the glacier was larger and thicker. Karsaglaciaren is thus out of synch with current geometry and climate and is exhibiting a 'thermal lag'. We propose that, with time, Karsaglaciaren's ablation zone and perhaps the entire glacier may well become fully cold as the temperate zone shrinks further. We anticipate that such a thermal lag is likely to be present within other Arctic glaciers. A thermal lag and an evolution to a fully cold thermal state have significant implications for the dynamic behaviour of small Arctic glaciers and for meltwater production from them.