| Summary: | Salts are widespread in the cold, arid McMurdo region of Antarctica. They exist in a variety of deposit types from massive subglacial and sub-lake deposits containing up to 1010 kilograms of salt, down to traces in soil, snow and ice. However, deposits on rock and soil typically amount to a few grams of salt. At least 30 salt phases are known but only 10 of these are widespread. These 10 are thenardite, gypsum, halite, calcite, darapskite, soda nitre, mirabilite, bloedite, epsomite and hexahydrite. The distribution of salts has been examined on two scales, local and regional. The local scale extends from individual deposits to areas of a few square kilometres. The regional scale covers McMurdo oasis, McMurdo Sound and Ross Island, though areas in McMurdo oasis, and particularly Taylor Valley receive most attention. Local distribution is controlled by salt migration and separation. Migration is induced by water and wind, with soil brines moving as thin liquid films, by capillarity and under the influence of gravity. Deflation and asymmetric salt accumulation provide evidence that wind is important. Separation of phases is a consequence of different physico-chemical properties of salts, and environmental conditions, including site aspect, ambient temperature and humidity. Eutectic temperature is a fundamental salt property but solubility is also important. Several salt deposits containing separated (fractionated) phases have been found in the region. Separation is achieved mainly by fractional dissolution and crystallization and the most evolved product of the general separation sequence is calcium chloride. The separation processes, together with salt migration, obscure the sources of the salts. Regional distribution of salts has been characterized by determining the relative frequency at which specific phases are encountered at increasing distance from the coast and above sea level. Chloride and sodium phases decrease, whereas magnesium phases increase in frequency away from the coast. Sulphates-to-chloride and ...
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