The impact of internal thermal regime of glaciers on climate caused advance and retreat

Most glaciers in Sweden have polythermal temperature regimes, where a temperate core of ice is overlain by a cold surface layer. The cold surface layer prolongs the response time of a glacier, and therefore increases the time it takes for a glacier to start advancing during a cooling climate trend. In the late 1980s and 1990s, some glaciers in Sweden advanced due to prolonged periods of positive mass balance, for example Storglaciären. However, far from all glaciers advanced during this period, coincidentally relating to their cold surface layer thickness. This raises the question: what factors drive how and when a polythermal glacier advances, and what climatic signals can be read from traces of past advances and extents? Here, four polythermal glaciers are described in detail since the early 1900s, when they were close to, or at, their largest Holocene extents. These glaciers lie in relatively similar settings, and thus share many resemblances, but also show many differences. How these glaciers have changed since the early 1900s, how they look today, and what landforms they have left behind, provides an opportunity to explore factors behind their responses. The four studied glaciers are: Mikkaglaciären, Storglaciären, Rabots glaciär, and Mårmaglaciären. The dynamics of glaciers retreating are much better understood than glaciers advancing, as the overwhelming majority of existing data have been collected since the latter 1900s half, during a period of overall negative mass balance. The aim of the study is to describe the current properties of the studied glaciers. Using this knowledge and the landform assemblages in their glacier forefields, we suggest explanations to how they might have responded to climate change in the past and possible causes for differences in their response.