1. 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2R3, Canada
2. 2Geography and Environmental Science, University of Southampton, Southampton SO17 1BJ, UK
3. 3School of Ocean and Earth Science, National Oceanography Centre, Southampton SO14 3ZH, UK
4. 4Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA
5. 5British Antarctic Survey, Natural Environment Research Council, Cambridge CB3 0ET, UK
6. 6Department of Geography, Durham University, Durham DH1 3LE, UK