1. Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK
2. The Lyell Centre, British Geological Survey, Edinburgh EH14 4AP, UK
3. School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand
4. Institute of Geosciences, University of Mainz, Becherweg 21, Mainz D-55099, Germany
5. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA