Interannual changes of the floating ice shelf of Petermann Gletscher, North Greenland, from 2000 to 2012

Petermann Gletscher, northwest Greenland, drains 4% of the Greenland ice sheet into Nares Strait. Its floating ice shelf retreated from 81 to 48 km in length during two large calving events in 2010 and 2012. We document changes in the three-dimensional ice-shelf structure from 2000 to 2012, using repeated tracks of airborne laser altimetry and ice radio-echo sounding, ICESat laser altimetry and MODIS visible imagery. The recent ice-shelf velocity, measured by tracking surface features between flights in 2010 and 2011, is �1.25 km a -1 , �15-30% faster than estimates made before 2010. The steady- state along-flow ice divergence represents 6.3 Gt a -1 mass loss through basal melting (�5 Gt a -1 ) and surface melting and sublimation (�1.0 Gt a -1 ). Airborne laser altimeter data reveal thinning, both along a thin central channel and on the thicker ambient ice shelf. From 2007 to 2010 the ice shelf thinned by �5 m a -1 , which represents a non-steady mass loss of �4.1 Gt a -1 . We suggest that thinning in the basal channels structurally weakened the ice shelf and may have played a role in the recent calving events.

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