Abstract
Abstract. Kronebreen and Kongsbreen are among the fastest-flowing glaciers on Svalbard and, therefore, important contributors to the total dynamic mass loss from the archipelago. Here, we present a time series of area-wide surface velocity fields from April 2012 to December 2013 based on offset tracking on repeat high-resolution Radarsat-2 Ultrafine data. Surface speeds reached up to 3.2 m d−1 near the calving front of Kronebreen in summer 2013 and 2.7 m d−1 at Kongsbreen in late autumn 2012. Additional velocity fields from Radarsat-1, Radarsat-2 and TerraSAR-X data since December 2007 together with continuous GPS measurements on Kronebreen since September 2008 revealed complex patterns in seasonal and interannual speed evolution. Part of the ice-flow variations seem closely linked to the amount and timing of surface meltwater production and rainfall, both of which are known to have a strong influence on the basal water pressure and hence basal lubrication. In addition, terminus retreat and the associated reduction in back stress appear to have influenced the speed close to the calving front, especially at Kongsbreen in 2012 and 2013. Since 2007, Kongsbreen retreated up to 1800 m, corresponding to a total area loss of 2.5 km2. In 2011 the retreat of Kronebreen of up to 850 m, responsible for a total area loss of 2.8 km2, was triggered after a phase of stable terminus position since ~ 1990. Retreat is an important component of the mass balance of both glaciers, in which frontal ablation is the largest component. Total frontal ablation between April 2012 and December 2013 was estimated to 0.21–0.25 Gt a−1 for Kronebreen and 0.14–0.16 Gt a−1 for Kongsbreen.
Highlights
Extended mass loss made glaciers the most important cryospheric contributors to global eustatic sea-level rise in the 20th century, and projections from surface mass balance models estimate additional loss of glaciers outside Antarctica of 0.07 to 0.26 m sea-level equivalent by 2100 (Church et al, 2013)
In the following two sections, we report on recent variations in flow speed, terminus position and frontal ablation of Kronebreen (Sect. 5.1) and Kongsbreen (Sect. 5.2)
Winter background speeds and summer speedup in 2010 had a medium amplitude compared to the following years (Figs. 5 and 6), coinciding with the lowest meltwater production during the observation period (CPDD2010 = 451 ◦C d)
Summary
Extended mass loss made glaciers the most important cryospheric contributors to global eustatic sea-level rise in the 20th century, and projections from surface mass balance models estimate additional loss of glaciers outside Antarctica of 0.07 to 0.26 m sea-level equivalent by 2100 (Church et al, 2013). These estimates do not yet include dynamic glacier wastage, which is poorly constrained but might play an important role over the course of the centuries (Church et al, 2013). The importance of frontal melt was first highlighted on LeConte glacier in Alaska by Motyka et al (2003), where melt was estimated to be 57 % of the total ice loss at the glacier front
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