Space-Time Evolution of Greenland Ice Sheet Elevation and Mass From Envisat and GRACE Data

Precise measurements of height changes (HCs) are important for improved estimates of mass balance of the Greenland Ice Sheet (GrIS). Here we determine 10 years of precise, high-resolution HCs of the GrIS from Envisat radar altimeter using a subwaveform retracker and a modified repeat-track method. The HCs show clear seasonal changes and monotonic declines over glaciers on the coasts such as Zachariae IsstrOm. We enhance mass change estimates from Gravity Recovery and Climate Experiment (GRACE) data using HCs and densities from interannual correlations between GRACE-derived mass changes and HCs. We estimate the mass changes of eight drainage basins with our combined mass change. The largest mass change between 2002 and 2012 occurred in the northwest basin and the smallest in the northeast basin. We separate the ice and snow HC rates to derive a ratio (f) between them to characterize the relative importance of ice or snow to mass change. The snow HC rates are mostly positive over the GrIS, except on the margins of the west coast and Zachariae IsstrOm. The mean ice HC rate is -6.6 3.9 cm/year over 2002-2006, which accelerated to -13.9 2.4 cm/year over 2007-2012. The f factors show a clear post-2006 ice dominance in the GrIS mass loss, particularly on the west coast, with a mean 91.4% ice contribution over 2002-2006, increasing to 94.5% over 2007-2012. This indicates increasing mass loss after 2006. A coincident radar altimeter and gravimetry mission is important for studying mass balance and separating snow and ice contributions over space and time.