Contrasting Regional Soil Alteration across the Topographic Dichotomy of Mars

Landscapes on either side of the martian topographic dichotomy bear distinct soil chemistry, but the processes associated with this distinction remain poorly understood. Here, correlation of soil chemistry at global to regional scales is examined with multivariate analysis of Gamma-Ray Spectrometer chemical maps and the Thermal Emission Spectrometer-derived Dust Cover Index (DCI). In the analysis, the northern lowlands show a strong S-Cl correlation, contrasting with the southern highlands, which show a stronger S-H2O correlation. These observations suggest aqueous interaction with soils throughout the southern highlands, preferentially dissolving Cl compounds and weakening S-Cl correlation. Strong S-Cl correlations in the northern lowlands suggest less interaction with aqueous H2O. Additionally, regional analyses demonstrate that DCI does not correlate with volatile chemistry at smaller scales and that Ca may be an important component of volatile-bearing material. These results provide new evidence for widespread aqueous interaction and possibly alteration of soil in the southern highlands.