1. Norwegian Polar Institute, Fram Centre, 9296 Tromsø, Norway
2. Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo, Norway
3. Institute of Ecology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
4. Department of Geography, University of Sheffield, Winter Street, S10 2TN Sheffield, U.K.