Chemical and isotopic switching within the subglacial environment of a high Arctic glacier General Research paper Peter Wynn a, *, Andrew Hodson a , Tim H.E. Heaton b a Department of Geography, University of Sheffield, Winter St., Sheffield S10 2TN, UK b NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK * Corresponding author. Tel. +44(0)114 222 7900. E-mail address: p.wynn@sheffield.ac.uk Keywords: Isotopes; Microbial; Redox status; Subglacial