Surface elevation change of outlet glaciers in northwestern Greenland for 1985-2010

Ice discharge from calving glaciers has increased in the Greenland ice sheet (GrIS), and this increase plays important roles in the volume change of GrIS and its contribution to sea level rise. Thinning of GrIS calving glaciers has been studied by differencing digital elevation models (DEMs) derived by satellite remote-sensing. Measurement period of such studies is limited by availability of satellite data, and thus surface elevation change of Greenlandic glaciers and ice caps are few for the period before the satellite era. In this study, we measured surface elevation change of marine-terminating Bowdoin and Sun Glaciers and land-terminating Tugto Glacier in northwestern Greenland (77°35'-77°56'N, 68°00'-69°45'W), using aerial photographs acquired in 1985 and recent satellite data. The aerial photographs taken by Danish National Survey were analyzed by the digital photogrammetric technique to derive DEMs with a 25 m grid mesh. We also generated DEMs on August 20, 2007 and September 4, 2010, by analyzing Advanced Land Observing Satellite (ALOS), Panchromatic remote-sensing Instrument for Stereo Mapping (PRISM) images. Vertical coordinates of DEMs were calibrated by comparing the elevation over a relatively flat (<10°) ice-free terrain. The standard deviation of elevation difference between 1985 and 2007 DEMs was 8.2 m. Mean surface elevation change over the glacier area of 507.49 km2 was -55.1 ± 8.2 m (-2.5 ± 0.4 m a-1) in 1985-2007. Elevation change near the terminus of Bowdoin Glacier increased from -2.5 to -5.5 m a-1 from 1985-2007 to 2007-2010, whereas the rate was similar over the two periods in Tugto Glacier. Our study demonstrated that recent acceleration in the mass loss is more significant in calving glaciers as compared with land-terminating glaciers. This result suggests the importance of ice dynamics and/or ice-ocean interaction in the mass loss of GrIS.