Dissociation of water in the Martian atmosphere may be supply oxygen to the surface and may result in the formation of minerals such as goethite, as proposed by Huguenin. The supply rate is limited by chemical processes in the atmosphere which regulate the abundance of O2. The net surface sink for atmospheric oxygen can be as large as 3.3¿107 atoms cm-2 sec-1 which compares to the escape rate of 6¿107 atoms cm-2 sec-1.