1. Department of Environmental Sciences, 2217 Geology Building, University of California, Riverside, California 92521
2. Institute of Arctic and Alpine Research and Department of Geography, University of Colorado at Boulder, UCB 450, Boulder, Colorado 80309-0450
3. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3
4. Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9