1. Scott Polar Research Institute, University of Cambridge, Lensfield Road, Cambridge CB2 1ER, UK
2. British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
3. Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
4. Department of Geodynamics and Sedimentology, Universitat Wien, Universitatsring 1, 1010 Vienna, Austria