1. Geological Institute; University of Bergen; Allegaten 41, 5007 Bergen Norway
2. Scripps Institution of Oceanography; University of California; La Jolla California 92093-0225 USA
3. Department of Microbiology; University of Bergen; Jahnebk. 5, 5007 Bergen Norway
4. Department of Geology; University of Alberta; Edmonton, Alta T6G 2E3 Canada