Abstract
Soils in ice-free areas in Antarctica are recognized for their high salt concentrations and persistent arid conditions. While previous studies have investigated the distribution of salts and potential sources in the McMurdo Dry Valleys, logistical constraints have limited our investigation and understanding of salt dynamics within the Transantarctic Mountains. We focused on the Shackleton Glacier (85° S, 176° W), a major outlet glacier of the East Antarctic Ice Sheet located in the Central Transantarctic Mountains (CTAM), and collected surface soil samples from 10 ice-free areas. Concentrations of water-soluble nitrate (NO3¬-) and sulfate (SO42-) ranged from <0.2 to ~150 µmol g-1 and <0.02 to ~450 µmol g-1, respectively. In general, salt concentrations increased with distance inland and with elevation. However, concentrations also increased with distance from current glacial ice position. To understand the source and formation of these salts, we measured the stable isotopes of dissolved NO3- and SO42-, and soil carbonate (HCO3- + CO32-). δ15N-NO3 values ranged from -47.8 to 20.4‰ and, while all δ17O-NO3 values are positive, they ranged from 15.7 to 45.9‰. δ34S-SO4 and δ18O-SO4 values ranged from 12.5 and 17.9‰ and -14.5 to -7.1‰, respectively. Total inorganic carbon isotopes in total bulk soil samples ranged from 0.2 to 8.5‰ for δ13C and -38.8 to -9.6‰ for δ18O. A simple mixing model indicates that NO3- is primarily derived from the troposphere (0-70%) and stratosphere (30-100%). SO42- is primarily derived from secondary atmospheric sulfate (SAS) by the oxidation of reduced sulfur gases and compounds in the atmosphere by H2O2, carbonyl sulfide (COS), and ozone. Calcite and perhaps nahcolite (NaHCO3) are formed through both slow and rapid freezing and/or the evaporation/sublimation of HCO3 + CO3-rich fluids. Our results indicate that origins of salts from ice-free areas within the CTAM represent a complex interplay of atmospheric deposition, chemical weathering, and post-depositional processes related to glacial history and persistent arid conditions. These findings have important implications for the use of these salts in deciphering past climate and atmospheric conditions, biological habitat suitability, glacial history, and can possibly aid in our future collective understanding of salt dynamics on Mars.
Highlights
Ice-free areas within the Transantarctic Mountains (TAM) have been of scientific interest throughout the 20th and 21st centuries due in part to their unique polar desert soil environments
We show that salt composition varies throughout the region, likely related to differences in the availability of water, and atmospheric deposition is the primary source of both NO3− and SO4−, while carbonate minerals are formed from the freezing and evaporation/sublimation of water
The relative enrichment of SO42− increases further away from the coast and closer to the Polar Plateau. Both nitrate and sulfate have a positive relationship with distance from the Ross Ice Shelf. These results show that, contrary to trends observed in the McMurdo Dry Valleys (MDV) and the Beardmore Glacier region (83◦4 S, 171◦0 E) where NO3− was the dominant salt for inland and high elevation locations, sulfate is instead the most abundant in the Shackleton Glacier region (Keys and Williams, 1981; Lyons et al, 2016)
Summary
Ice-free areas within the Transantarctic Mountains (TAM) have been of scientific interest throughout the 20th and 21st centuries due in part to their unique polar desert soil environments. They are characterized by average annual temperatures below freezing, low amounts of precipitation, and low biomass. Geochemical work in the McMurdo Dry Valleys (MDV) (77◦ S, 162◦ E), the largest ice-free area in Antarctica, showed that the soil environments in Antarctica are among the most saline systems on Earth (Jones and Faure, 1967; Keys and Williams, 1981). Antarctic ice-free environments are often utilized as Martian analogs, and salt formation processes in Antarctica may aid in our understanding of salt sources and the current and past availability of water on Mars (Wynn-Williams and Edwards, 2000; Vaniman et al, 2004; Bishop et al, 2015)
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