| Popis: |
Evaporite salts from saline lakes and playas play active roles in the atmospheric cycles and the climate system, especially in the context of changing climate. Similar processes also occurred on Mars, where large water bodies dried up and formed saline lakes and then salt evaporites and deposits. In this study, various salt samples (brines, lakebed salts, crust salts, playa surface salts, and a series of salts collected at different depths) were collected from two Martian analogue sites (Mang’ai and Dalangtan, MA and DLT) in Qaidam Basin. The salt samples were measured for their ionic compositions and pH as the fundamental characterization, and the effects of sample types and sampling sites are discussed. The hygroscopic properties of solid salts, including crystalized brines, were experimentally determined. The results show strong connections between the ionic composition and hygroscopic properties though discrepancy exists, indicating that the hygroscopicity is sensitive to the molecular forms and the hydrate degrees of salts. Sulfur and chlorine isotopes were measured, and the results are presented as δ34S and δ37Cl. The δ34S values of samples from MA and DLT show great difference. The δ34S values of MA samples are comparable to previously reported fresh water, brines and local precipitation, indicating that the MA samples are strongly influenced by materials exchanged from local environments. The DLT samples have higher δ34S values, which suggest that the material exchanges with surrounding environments are limited. The δ37Cl values are confined within a relatively narrow window compared to literature values. A trend is that the δ37Cl values vary with sample types, i.e., crust > lakebed > brine. This is likely caused by the isotopic fractionation during evaporite precipitation, where the heavier 37Cl isotope is preferably precipitated. The study of salt samples from MA and DLT areas improves the understanding of the active role of evaporite salts in the material cycle and climate system of both Earth and Mars.Keywords: δ34S, δ37Cl, hygroscopicity, climate, Mars, Qaidam Basin |
