Assessment of differentiated surface elevation data from 1949, 1975 and 2008 for estimates of ice-volume changes at Jan Mayen

The volcanic island Jan Mayen (70 degree 59'14"N, 8 degree 28'54"W; area 373 km super(2)) is situated in the North Atlantic Ocean between Iceland and Svalbard (Fig. 1a). A reduction in ice volume has been observed since the mid-1990s for glaciers in Iceland (Bjornsson and Palsson, 2008; Pope and others, 2010; Cudmundsson and others, 2011) and in the western and southern parts of Svalbard (Nuth and others, 2010), and it is of interest to determine whether the same is true for Jan Mayen glaciers, where very few glaciological data are available. Twenty glaciers covering 105 km super(2) flow down from the central Berenberg crater (2277 ma.s.l.). The direct glaciological mass balance of one glacier, Sorbreen (area similar to 15km super(2); Fig. 1b), was measured in 1972-74 and 1976-77 (Orheim 1976; Hagen, 1993), and new measurements were initiated in 2008 (Hulth and others, 2010). However, these sparse surface mass-balance data do not give adequate information on the total ice-volume changes. Neither has any mass-balance modeling been conducted, even though the Norwegian Meteorological Institute has measured meteorological data on the island since 1921 (location shown in Fig. 1 b). We have therefore conducted an assessment of the existing elevation data from oblique and vertical aerial photographs, and a SPOT 5 (Systeme Probatoire pour I'Observation de la Terre) stereoscopic survey in order to provide initial information on the current status of the ice-volume changes, and to evaluate the need for new measurements to determine the complete geodetic mass balance of Jan Mayen.