Sulphide oxidation under partially anoxic conditions at the bed of the Haut Glacier d'Arolla, Switzerland

Oxygen isotopic data are presented for bulk glacial meltwaters draining the Haut Glacier d'Arolla, Valais, Switzerland and for the sulphate contained within them in an attempt to assess the redox status of the subglacial chemical weathering environment. The sulphate derived from subglacial chemical weathering is so depleted in O-18 that it must have formed, at least partially, in an anoxic environment. Under these conditions, Fe3+ can act as an oxidizing agent and oxygen atoms incorporated into sulphate are derived from O-18-depleted water molecules (by contrast, dissolved O-2 is strongly enriched in O-18). These data therefore support the hypothesis that sectors of the glacier bed are anoxic and that Fe3+ may act as a significant oxidizing agent under these conditions. Copyright (C) 2002 John Wiley Sons, Ltd.