Satellite-derived volume loss rates and glacier speeds for the Cordillera Darwin Icefield, Chile

We produce the first icefield-wide volume change rate and glacier velocity estimates for the Cordillera Darwin Icefield (CDI), a 2605 km(2) temperate icefield in southern Chile (69.6A degrees W, 54.6A degrees S). Velocities are measured from optical and radar imagery between 2001-2011. Thirty-six digital elevation models (DEMs) from ASTER and the SRTM DEM are stacked and a weighted linear regression is applied to elevations on a pixel-by-pixel basis to estimate volume change rates. The CDI lost mass at an average rate of -3.9 +/- 1.5 Gt yr(-1) between 2000 and 2011, equivalent to a sea level rise (SLR) of 0.01 +/- 0.004 mm yr(-1) and an area-averaged thinning rate of -1.5 +/- 0.6 m w.e.(water equivalent) yr(-1). Thinning is widespread, with concentrations near the front of two northern glaciers (Marinelli, Darwin) and one western (CDI-08) glacier. Thickening is apparent in the south, most notably over the advancing Garibaldi Glacier. The northeastern part of the CDI has an average thinning rate of -1.9 +/- 0.7 m w.e. yr(-1), while the southwestern part has an average thinning rate of -1.0 +/- 0.4 m w.e. yr(-1). Velocities are obtained over many of the CDI glaciers for the first time. We provide a repeat speed time series at the Marinelli Glacier. There we measure maximum front speeds of 7.5 +/- 0.2 m day(-1) in 2001, 9.5 +/- 0.6 m day(-1) in 2003 and 10 +/- 0.3 m day(-1) in 2011. The maintenance of high front speeds from 2001 to 2011 supports the hypothesis that Marinelli is in the retreat phase of the tidewater cycle, with dynamic thinning governed by the fjord bathymetry.