1. Scott Polar Research Institute, Department of Geography; University of Cambridge; Cambridge; CB2 3EN; UK
2. Norwegian Water Resources and Energy Directorate (NVE); P.O. Box 5091; Majorstuen; N-0301; Oslo; Norway
3. Institute for Marine and Atmospheric Research Utrecht (IMAU); Utrecht; P.O. Box 80.005; NL-3508 TA; Utrecht; The Netherlands