Mass balance of Mýrdalsjökull ice cap accumulation area and comparison of observed winter balance with simulated precipitation

Abstract

The Mýrdalsjökull ice cap at the south coast of Iceland receives precipitation from the frequently passing extratropical lows, making the region the wettest in Iceland. Most of the ice cap’s accumulation area is a gently sloping plateau (1350–1510 m a.s.l.) within the caldera rim of Katla central volcano, feeding large outlets to the north and east. The oldest mass balance survey data are from 1944 and 1955. Here, mass balance measurements on the plateau, carried out 2001 and annually since 2007, are described and analyzed. Additionally, the winter mass balance is compared with precipitation estimates based on synoptic observations of precipitation at sea level and from high-resolution numerical simulations made with an atmospheric model. The measured specific winter balance at four locations above the equilibrium line was in the range 3.4–7.8 m w.e. (water equivalent) with a maximum winter snow thickness in excess of 12 m. The summer mass balance was highly variable (–0.9 – –3.1 m w.e.) and the annual mass balance at the plateau had a high spatial and temporal variability (2.1–5.9 m w.e.). A comparison between measured winter balance and observations of precipitation at sea level, suggests that the plateau of Mýrdalsjökull receives on average 1–1.8 m w.e. of precipitation during summer. Results from the atmospheric simulations compare well with the measured winter balance and the estimated summer precipitation at the survey sites. The winter balance as well as the precipitation are among the highest reported in Iceland, and parts of the ice cap may annually receive up to 10 m w.e. of precipitation.