1. Researcher, Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Cambridge, MA 02139 (corresponding author).
2. Researcher, Dept. of Earth and Environmental Sciences, Columbia Univ., New York, NY 10025.
3. Researcher, Dept. of Earth and Environmental Engineering, Columbia Univ., New York, NY 10027.
4. Ph.D. Candidate, Scripps Institution of Oceanography, Univ. of California San Diego, La Jolla, CA 92093.
5. Ph.D. Candidate, College of Earth, Ocean and Atmospheric Sciences, Oregon State Univ., Corvallis, OR 97331.