Izzy’s coauthors were Jessica Johnson, Lingfeng Kuang, Sophie Naylor, Tommy Subak, Alison Koleszar, and Joe Levy from Colgate University in New York.

Izzy is a scientist based in Washington, DC, who focuses on geochemistry, hydrology, and water and soil contamination.

The GSA Bulletin is a leading international journal for major scholarly research in all branches of the earth sciences and has been published continuously since 1890.

The Geological Society of America, founded in 1888, is a global scientific society with members from academia, government, and industry in more than 100 countries. Through its meetings, publications, and programs, the society enhances the professional growth of geoscientists, encourages cooperative research, fosters public dialogue on geoscience issues, and promotes geosciences in the service of humankind.

Abstract

Groundwater in the McMurdo Dry Valleys of Antarctica is commonly enriched in calcium and chloride, in contrast to surface and groundwater in temperate regions, where calcium chemistry is largely controlled by the dissolution of carbonates and sulfates. These Antarctic Ca-Cl brines have extremely low freezing points, which leads to moist soil conditions that persist unfrozen and resist evaporation, even in cold, arid conditions. Several hypotheses exist to explain these unusual excess-calcium solutions, including salt deliquescence and differential salt mobility and cation exchange. Although the cation-exchange mechanism was shown to explain the chemistry of pore waters in permafrost cores from several meters’ depth, it has not been evaluated for near-surface groundwater and wetland features (water tracks) in which excess-calcium pore-water solutions are common. Here, we use soluble salt and exchangeable cation concentrations to determine whether excess calcium is present in water-track brines and if cation exchange could be responsible for calcium enrichment in these cold desert groundwaters. We show that calcium enrichment by cation exchange is not occurring universally across the McMurdo Dry Valleys. Instead, evidence of the present-day formation of Ca-Cl-rich brines by cation exchange is focused in a geographically specific location in Taylor Valley, with hydrological position, microclimate, soil depth, and organic matter influencing the spatial extent of cation-exchange reactions. Up-valley sites may be too cold and dry for widespread exchange, and warm and wet coastal sites are interpreted to host sediments whose exchange reactions have already gone to completion. We argue that exchangeable cation ratios can be used as a signature of past freeze-concentration of brines and exchange reactions, and thus could be considered a geochemical proxy for past groundwater presence in planetary permafrost settings. Correlations between water-track organic matter, fine-sediment concentration, and cation-exchange capacity suggest that water tracks may be sites of enhanced biogeochemical cycling in cold desert soils and serve as a model for predicting how active layers in the Antarctic will participate in biogeochemical cycling during periods of future thaw.

More Information

Learn more about the article: Brine Formation in Cold Desert, Shallow Groundwater Systems: Antarctic Ca-Cl Brine Chemistry Controlled by Cation Exchange, Microclimate, and Organic Matter
Learn more about the journal: GSA Bulletin
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