1. Department of Earth and Space Sciences; University of Washington; Seattle WA USA
2. Department of Atmospheric Sciences; University of Washington; Seattle WA USA
3. UJF - Grenoble 1 / CNRS; Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE) UMR 5183; Grenoble F-38041 France
4. Department of Chemistry and Biochemistry; University of California San Diego; La Jolla CA USA