Greenland: Bringing together remote sensing and fieldwork.
With global land and sea temperatures rising, the importance of accurate monitoring of the world's ice sheets is increasing. Satellite radar altimetry can be used to measure elevation changes of ice sheets from which mass balance can be derived. In the percolation zone of ice sheets, summer melt which percolates into the snowpack and refreezes causes a re-distribution of mass through densification, which can result in elevation changes which are not representative of changes in mass balance. We present data collected in the percolation zone of the Greenland Ice Sheet prior to and post the processes of summer melt, percolation and refreezing. Data from nine sites along two 1-km transects show that in 2004 there was a 31.6% increase in accumulation over the summer, but due to surface melting percolation and refreezing the average snowpack density increased by 26.2%, resulting in only a 5.3% increase in elevation. Our results indicate that in areas of substantial seasonal melt and refreezing, densification rates must be accurately quantified if mass balance estimates are to be usefully derived from surface elevation change.