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Though the majority of the Antarctic continent is covered by ice, portions of Antarctica, mainly in the McMurdo Dry Valleys and the Transantarctic Mountains (TAM), are currently ice-free. The soils which have developed on these surfaces have been re-worked by the advance and retreat of glaciers since at least the Miocene. They are generally characterized by high salt concentrations, low amounts of organic carbon, and low soil moisture in a polar desert regime. Ecosystems that have developed in these soils have few taxa and simplistic dynamics, and can therefore help us understand how ecosystems structure and function following large-scale changes in climate, such as glacial advance and retreat. During the 2017-2018 austral summer, 220 surface soil samples and 25 depth profile samples were collected from eleven ice-free areas along the Shackleton Glacier, a major outlet glacier of the East Antarctic Ice Sheet. A subset of 27 samples were leached at a 1:5 soil to deionized (DI) water ratio and analyzed for stable isotopes of water-soluble NO3- (δ15N and Δ17O) and SO42- (δ34S and δ18O), and seven soils were analyzed for δ13C and δ18O of HCO3 + CO3 to understand the sources and cycling of salts in TAM soils. The depth profiles and a subset of surface soil (21) samples were analyzed for concentrations of meteoric 10Be and/or water-soluble NO¬3- to estimate relative surface exposure ages along the length of the Shackleton Glacier. Finally, water-soluble ion data from all 220 samples were correlated with geography and geomorphology to elucidate geochemical trends and gradients. The relationship between geochemistry and geography was further used to predict/estimate geochemical gradients in the TAM using interpolation and machine learning techniques. Collectively, these measurements and data show that atmospheric deposition is an important source of water-soluble anions, which have possibly been accumulating in some soils since at least the Pleistocene. Soils near the terminus of the Shackleton Glacier and near the glacier margins are younger than those further south towards the Polar Plateau and further inland. These soils have nutrient and salt concentrations most suitable for soil invertebrates. The geochemistry of TAM soils is related to geography, glacial history, and the present and past availability of liquid water, and these parameters can be used to effectively predict/model geochemical gradients. These findings will greatly aid in our collective understanding of habitat suitability and past refugia in Antarctic terrestrial systems, and may help predict how ecosystems will respond to future climate transitions.

Aeolian processes play an important role in the transport of both geological and biological materials globally, on the biogeochemistry of ecosystems, and in landscape evolution. As the largest ice free area on the Antarctic continent (approximately 4800 km2), the McMurdo Dry Valleys (MDV) are potentially a major source of aeolian material for Antarctica, but information on the spatial and temporal variability of this material is needed to understand its soluble and bulk geochemistry, deposition and source, and hence influence on ecosystem dynamics. 53 samples of aeolian material from Alatna Valley, Victoria Valley, Miers Valley, and Taylor Valley (Taylor Glacier, East Lake Bonney, F6 (Lake Fryxell), and Explorer’s Cove) were collected at five heights (5, 10, 20, 50, 100 cm) above the surface seasonally for 2013 through 2015. The sediment was analyzed for soluble solids, total and organic carbon, minerology, and bulk chemistry. Of the soluble component, the major anions varied between Cl- and HCO3-, and the major cation was Na+ for all sites. Soluble N:P ratios in the aeolian material reflect nutrient limitations seen in MDV soils, where younger, coastal soils are N-limited, while older, up valley soils are P-limited. Material from East Lake Bonney was P-limited in the winter samples, but N-limited in the full year samples, suggesting different sources of material based on season. Analysis of soluble salts in aeolian material in Taylor Valley compared to published soil literature demonstrates a primarily down valley transport of materials from Taylor Glacier towards the coast. The bulk chemistry suggests that the aeolian material is highly unweathered (CIA values less than 60 %), but scanning electron microscope images show alteration for some individual sediment grains. The mineralogy was reflective of local rocks, specifically the McMurdo Volcanics, Ferrar Dolerite, Beacon Sandstone and granite, but variations in major oxide percentages and rare earth element signatures could not be explained by mixing lines between these four rock types. This potentially suggests that there may be an additional, and possibly distant, source of aeolian material to the MDV that is not accounted for. This work provides the first fully elevated spatial and temporal analysis of the geochemistry of aeolian material from the Dry Valleys, and contributes to a better understanding of sediment provenance and how aeolian deposition may affect surface biological communities.