The salt fraction in permafrost soils/sediments of the McMurdo Dry Valleys (MDV) of Antarctica can be used as a proxy for cold desert geochemical processes and paleoclimate reconstruction. Previous analyses of the salt fraction in permafrost soils have largely been conducted in coastal regions where permafrost soils are variably affected by aqueous processes and mixed inputs from marine and stratospheric sources. We expand upon this work by evaluating permafrost soil/sediments in University Valley, located in the ultraxerous zone where both liquid water transport and marine influences are minimal. We determined the abundances of Cl-, NO 3

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Recent investigations have reported a widespread occurrence of chlorate (ClO 3 − ) and perchlorate (ClO 4 − ) throughout the solar system, including terrestrial arid environments. ClO 3 − and ClO 4 − are deposited/ accumulated at an approximate equal molar ratio, with some exceptions, such as the Antarctica Dry Valley soils (MDV) and perhaps Martian surface material, where ClO 4 − is the dominate ClO x − species. All known ClO 4 − production mechanisms produce molar ratios of ClO 3 − /ClO 4 − equal to or much greater than 1, suggesting that reduced ratios may be due to post-depositional mechanism(s). The objective of this study was to investigate potential iron-mediated abiotic reduction of ClO 3 − , similar to transformation mechanisms reported for nitrate (NO 3 − ) by Fe(II) minerals. Three types of Fe(II)-containing minerals, wustite (FeO), siderite (FeCO 3 ), and sulfate green rust (GR SO4 2− ), were investigated in completely mixed batch reactors as potential ClO 3 − reductants at a range of pH (4− 9) and iron mineral concentrations (1−10 g/L). ClO 3 − was stoichiometrically reduced to chloride (Cl − ) by wustite, siderite, and green rust, but no transformation occurred by dissolved Fe(II). Wustite and green rust reduced NO 3 − but not by siderite. When both NO 3 − and ClO 3 − are reduced simultaneously, ClO 3 − is reduced preferentially to NO 3 − , although the effect is somewhat concentration-dependent. An increased background salt concentration (NaCl) increased ClO 3 − reduction but decreased NO 3 − . The stability of ClO 3 − and subsequent impacts on the ratio of ClO 3 − /ClO 4 − in the environment have implications for understanding the cycling of oxyanions and stability of iron minerals, and related to this, the ratio of ClO 4 − and ClO 3 − may be an indicator of the past availability of free water. On Mars, these reactions may help to explain the unusually high concentrations of ClO 4 − compared to ClO 3 − and NO 3 − .

Due to the high volume of crude oil released by the Deepwater Horizon oil spill, the salt marshes along the gulf coast were contaminated with crude oil. Biodegradation of crude oil in salt marshes is primarily limited by oxygen availability due to the high organic carbon content of the soil, high flux rate of S(2-), and saturated conditions. Chlorate, nitrate, and perchlorate were evaluated for use as electron acceptors in comparison to oxygen by comparing oil transformation and mineralization in mesocosms consisting of oiled salt marsh sediment from an area impacted by the BP Horizon oil spill. Mineralization rates were determined by measuring CO2 production and δ (13)C of the produced CO2 and compared to transformation evaluated by measuring the alkane/hopane ratios over a 4-month period. Total alkane/hopane ratios decreased (~55-70 %) for all treatments in the following relative order: aerated ≈ chlorate > nitrate > perchlorate. Total CO2 produced was similar between treatments ranging from 550-700 mg CO2-C. The δ (13)C-CO2 values generally ranged between the indigenous carbon and oil values (-17 and -27‰, respectively). Oil mineralization was greatest for the aerated treatments and least for the perchlorate amended. Our results indicate that chlorate has a similar potential as oxygen to support oil mineralization in contaminated salt marshes, but nitrate and perchlorate were less effective. The use of chlorate as a means to promote oil mineralization in situ may be a promising means to remediate contaminated salt marshes while preventing unwanted secondary impacts related to nutrient management as in the case of nitrate amendments.

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