Spatial Elevation Changes Observed at Helheim Glacier, Southeast Greenland, and Comparison with Kangerlussuaq Glacier and Jakobshavn Isbræ

Abstract:

Recent studies have shown that mass loss from Southeast Greenland is a significant percentage (~50%) of total ice loss from the entire Greenland Ice Sheet (GrIS). The greatest contributors to SE GrIS mass loss are the marine-terminating outlet glaciers Helheim and Kangerlussuaq. Since the early 2000s, the behavior of Kangerlussuaq Glacier can be characterized as a simple diffusion thinning event, with dramatic thinning commencing at the calving front in 2004 and then diffusing upglacier. Helheim Glacier, however, experienced a dramatic thinning event (~50 m) in 2004 with an abrupt cessation in 2006, followed by a sequence of thickening/thinning events of lesser magnitude from 2006 - 2012. This complex behavior is further investigated using multi-sensor surface elevation data over a broad region (~200 km²) of the glacier trunk during the period of 1981 - 2012. This dataset provides a highly accurate record of elevation changes for Helheim Glacier, and demonstrates that the onset of the rapid thinning event occurred over most of the glacier trunk rather than at the calving front. At the commencement of the rapid thinning event, Helheim Glacier’s calving front appeared to be grounded. This is in contrast to Kangerlussuaq Glacier and Jakobshavn Isbræ, which were approaching flotation prior to their rapid thinning events in 2004 and 1999, respectively. Additionally, the new dataset reveals curvilinear bands (≥1 km long, ≥100 m wide) of significant elevation change (≥10 m) compared to the surrounding ice, corresponding to lateral shear zones and tributary confluence junctions. Ice velocity data will also be examined at similar temporal and spatial scales as the elevation dataset to reconstruct an accurate timeline of events for Helheim Glacier and better determine the cause of the observed complex behavior.