Recent studies on the evolution of the Martian H2O inventory (pdf, 490 KB) show a huge surface sink for O atoms. The evidence for such an oxygen surface sink agrees with multi-spectral data analysis of Mars Pathfinder soils. The initial Fe3+/Fetot ratio in MER-A basalts is close to 0.16, whereas MER-A soils posses final Fe3+/Fetot ratios of about 0.28. Most of sulfur stems from volcanic emanation, which may comprise H2S and SO2. About 1x1021 to 3.5x1021 oxygen atoms per cubic centimeter mean soil are sequestered, given the soil density to be 1.5 g cm-3.

The primary source for molecular oxygen and hydrogen in the Martian atmosphere is the dissociation of water at high atmospheric altitudes. It has been shown that the loss rates of hydrogen due to escape to space and the rates of oxygen loss are misbalanced (Martian H₂O inventory). Significant amounts of oxygen appear to have been lost into the Martian surface due to oxidation of Martian soil. Based on the estimate that about 2x10⁴² oxygen atoms were sequestered by oxidation of surface material an average thickness of 14 to 4 meters for the global layer of oxidized soil can be derived. This implies that sulphuric hydrogen may represent an important component in volcanic gas emanated. Assuming a soil cover of 5 m with 3wt% S, about 10¹⁸ mol S are stored in the soil horizon. Such an amount would correspond to an ideal volcanic gas column of approximately 150 m under standard conditions, released and subsequently sequestered over the geologic history of the planet.