The soils of Antarctica are for the most part formed in the absence of biological processes and, as a consequence of the prevailing low temperatures, are everywhere underlain by permafrost, with the active layer varying in thickness from about one metre in northern areas to a few centimeters or less in the soils of the inland edge of the Transantarctic Mountains. The permafrost is generally ice-cemented, but in older and drier soils may be loose. Because of the extreme aridity, the soils accumulate salts derived from precipitation and weathering, the composition and amount of the salts being a function of soil age, composition of the parent material and distance from the coast. Chemical weathering processes are assisted by the salts, which allow unfrozen saline solutions to be present on grain surfaces and cracks in rock particles, even at very low temperatures. Weathering comprises the breakdown of ferreomagnesian minerals, releasing iron and cations to the soil solution. The iron oxidises and is precipitated on grain surfaces, giving rise to the red colouring of older soils. The cations, especially calcium and magnesium, combine with nitric and sulphuric acids arriving in precipitation, to make up part of the thick salt horizons which are found in older soils. The concentrated salt solutions react with silica, also released by weathering, to form secondary clay minerals and in some cases, zeolites.

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