1. Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755, USA.
2. Quaternary Isotope Laboratory, University of Washington, Seattle, WA 98195, USA.
3. Glacier Research Group, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824, USA.
4. Department of Physics, State University of New York at Buffalo, Amherst, NY 14260, USA.
5. Desert Research Institute, Reno, NV 89506, USA.
6. Department of Geophysics, University of Washington, Seattle, WA, 98195, USA.