1. Department of Earth and Environmental Sciences, Columbia University, Lamont‐Doherty Earth Observatory, Palisades, New York 10964.
2. Lamont‐Doherty Earth Observatory of Columbia University, Route 9W, Palisades, New York 10964-8000.
3. Naval Research Laboratory, Code 7420, 4555 Overlook Avenue SW, Washington, District of Columbia 20375-5350.