1. Department of Geology; University at Buffalo; Buffalo NY 14260 USA
2. Department of Earth Science; University of Bergen, and Bjerknes Centre for Climate Research; N-5020, Bergen Norway
3. Lamont-Doherty Earth Observatory of Columbia University; Palisades NY 10964 USA
4. School of Geographical and Earth Sciences; University of Glasgow; Glasgow G12 8QQ Scotland UK
5. Scottish Universities Environmental Research Centre; AMS Laboratory; East Kilbride G75 0QF Scotland UK
6. Department of Arctic Geology; The University Centre in Svalbard; Longyearbyen Norway
7. Department of Earth Sciences; University of Gothenburg; Gothenburg SE-405 30 Sweden