DESCRIPTION AND DISTRIBUTION OF COLD DESERT SALTS IN THE MCMURDO REGION, ANTARCTICA

Evaporite salts found in the McMurdo region, Antarctica (~78° S) are produced from the evaporation of soil moisture and are preserved because of very low precipitation, low relative humidity, and lack of any overland flow. Hygroscopic salts in the Dry Valleys are preferentially formed in locations where liquid water is present in the austral summer, including along streams and lake boundaries or shallow groundwater tracks. Chemical composition of these salts is related to landscape position, and is influenced by the path, flow and subsequent evaporation of liquid water. In this research, salts were collected in Miers, Garwood, Taylor Valley, and McMurdo Station in close proximity to water sources. A salt leach extraction with deionized water was performed to investigate the primary ion constituents. In order to ascertain the processes governing the evaporation sequence of subsurface flow, geochemical modeling using FREZCHEM was conducted. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) indicate a wide geochemical and morphological variety of salts within a relatively short (30km) area. Halite is ubiquitous as sodium is the major cation (averaging 70%-90% of cations by meq/kg sediment) and chloride is the major anion (>50%) in nearly all samples. However, a wide variety of salt phases are identified (including mirabilite, nahcolite, and the previously undocumented glauberite) possibly reflecting a different source and evaporitic evolution of the source water. Ion concentrations in the soils sampled range from 0-8000 milli-equivalents per kilogram of soil, and salt chemistries cannot be completely explained by simple processes such as sublimation of snow or evaporation of stream water. Implications for the salt distributions include their use as tracers for paleolake levels, recorders of water tracks or “wet patches,” as indicators of chemical weathering products, and to potentially delineate ecological communities.