[1] Univ Washington, Quaternary Res Ctr, Seattle, WA 98195 USA
[2] Univ Washington, Dept Earth & Space Sci, Seattle, WA 98195 USA
[3] Univ Washington, Dept Atmospher Sci, Seattle, WA 98195 USA
[4] Pacific Lutheran Univ, Dept Geosci, Tacoma, WA 98447 USA
[5] Univ Washington, Appl Phys Lab, Seattle, WA 98105 USA
[6] Univ Copenhagen, Niels Bohr Inst, DK-2100 Copenhagen, Denmark
[7] Univ Colorado, Inst Arctic & Alpine Res, Boulder, CO 80309 USA