Glaciar Upsala, Patagonia: rapid calving retreat in fresh water

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Abstract
The calving rates and calving styles of temperate glaciers that calve into fresh water are distinctively different from those of temperate tide-water glaciers. These contrasts are important for interpreting and predicting the response of ice masses to climate change. Glaciar Upsala is a large calving outlet of Hielo Patagónico Sur (southern Patagonia ice field). Its twentieth-century retreat has been climate-driven but significantly modulated by calving dynamics and by the transition from melting to calving at its eastern terminus. Here, the onset of rapid calving in the early 1980s initiated retreat at ≤440 m a−1. The 1992–93 calving rate (v c) is estimated to be 60 m a−1 in a mean water depth (h w) of 67 m. A v c/h w relationship for fresh water based on 14 sites around the world, including seven deep-water sites, confirms both the linear dependency of v c on h w and the contrast between calving rates in tide water and fresh water. As yet, no physical explanation for this contrast exists, but differences in subaqueous melt rates, longitudinal strain rates and crevassing may provide a partial explanation.