1. Environmental Change Research Centre; Department of Geography; University College London; Gower Street London WC1E 6BT UK
2. Lancaster Environment Centre; Lancaster University; Lancaster LA1 4YQ UK
3. NERC Isotope Geosciences Facilities, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK and Centre for Environmental Geochemistry, School of Geography; University of Nottingham; Nottingham NG7 2RD UK