1. BP Institute University of Cambridge Madingley Road Cambridge CB3 0EZ UK
2. Earth and Planetary Sciences Department Washington University in St Louis Campus Box 1169, 1 Brookings Drive Saint Louis MO 63130 USA
3. Department of Earth Sciences University of Cambridge Downing Street Cambridge CB2 3EQ UK
4. Department of Mathematics and Statistics University of Strathclyde 26 Richmond Street Glasgow G1 1XH UK
5. National Oceanography Centre University of Southampton Waterfront Campus, European Way Southampton SO14 3ZH UK