1. NERC Isotope Geosciences Laboratory; Kingsley Dunham Centre; Keyworth UK, NG12 5GG,
2. Department of Earth Sciences; University of Cardiff; UK, CF10 3YE,
3. Grant Institute; University of Edinburgh; Edinburgh UK, EH9 3JW,
4. Lamont-Doherty Geological Observatory and Department of Geological Sciences of Columbia University; Palisades New York 10964 USA
5. College of Oceanic and Atmospheric Sciences; Oregon State University; Oceanography Administration Building 104, Corvallis Oregon 97331 USA