Ice-volume changes (1936-1990) and structure of Aldegondabreen, Spitsbergen

Abstract

Aldegondabreen is a small valley glacier, ending on land, located in the Grønfjorden area of Spitsbergen, Svalbard. Airborne radio-echo sounding in 1974/75, using a 440 MHz radar, revealed a polythermal two-layered structure, which has been confirmed by detailed ground-based radio-echo sounding done in 1999 using a 15 MHz monopulse radar. The 1999 radar data reveal an upper cold layer extending down to 90 m depth in the southern part of the glacier, where the thickest ice (216 m) was also found. A repeated pattern of diffractions from the southern part of the glacier, at depths of 50-80 m and dipping down-glacier, has been interpreted as an englacial channel which originates in the temperate ice. From joint analysis of the 1936 topographic map, a digital elevation model constructed from 1990 aerial photographs and the subglacial topography determined from radar data, a severe loss of mass during the period 1936-90 has been estimated: a glacier tongue retreat of 930 m, a decrease in area from 8.9 to 7.6 km2, in average ice thickness from 101 to 73 m and in ice volume from 0.950 to 0.558 km3, which are equivalent to an average annual balance of -0.7 m w.e. This is comparable with the only available data of net mass balance for Aldegondabreen (-1.1 and -1.35 m w.e. for the balance years 1976/77 and 2002/03) and consistent with the 0.27°C increase in mean summer air temperature in this zone during 1936-90, as well as the warming in Spitsbergen following the end of the Little Ice Age (LIA), and the general glacier recession trend observed in this region.