1. Department of Chemistry; University of Florence; Florence Italy
2. Department of Physical Geography and Quaternary Geology; Stockholm University; Stockholm Sweden
3. Physics Institute; University of Bern; Bern Switzerland
4. Laboratoire de Glaciologie et Géophysique de l'Environnement du CNRS; Saint-Martin-d'Heres Cedex France
5. Earth and Environmental Science Program; New York University; New York New York USA
6. Department of Geophysics, Niels Bohr Institute; University of Copenhagen; Copenhagen Denmark