1. Scott Polar Research Institute, University of Cambridge, Cambridge CB2 1ER, UK
2. GRC Geociències Marines, Universitat de Barcelona, 08028 Barcelona, Spain
3. Department of Geological Sciences, Stockholm University, Svante Arrhenius väg 8, 106 91 Stockholm, Sweden
4. Geological Survey of Canada, Natural Resources Canada, PO Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada
5. British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK