1. Geochemical and Environmental Research Group, 10 South Graham Road, Department of Oceanography, Texas A&M University, College Station, TX 77840.
2. Oceanic Biology Group, Marine Science Institute, and Department of Biological Science, University of California, Santa Barbara, CA 93106.
3. Department of Earth Sciences, Memorial University, St. Johns, Newfoundland, Canada A1BX5.
4. Center for Applied Isotope Studies, University of Georgia, Athens, GA 30605.
5. Marine Biology Research Division, Scripps Institution of Oceanography, La Jolla, CA 92093.