1. Scott Polar Research Institute, University of Cambridge, Cambridge CB2 1ER, United Kingdom
2. Earth & Planetary Sciences, University of California, Santa Cruz, CA 95064
3. Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, United Kingdom
4. Department of Glaciology and Climate, Geological Survey of Denmark and Greenland, 1350 Copenhagen, Denmark
5. British Antarctic Survey, Natural Environment Research Council, Cambridge CB3 0ET, United Kingdom
6. National Institute for Water and Atmospheric Research, Wellington 6241, New Zealand