National Aeronautics and Space Administration



W. Andrew Jackson, Texas Tech UniversityFollow
J. K. Böhlke, U.S. Geological Survey, 431 National Center, Reston, VA
Brian J. Andraski, U.S. Geological Survey, 2730 N. Deer Run Rd, Carson City, NV
Lynne Fahlquist, U.S. Geological Survey, 1505 Ferguson Ln, Austin, TX
Laura Bexfield, U.S. Geological Survey, 5338 Montgomery Blvd. NE, Suite 400, Albuquerque, NM
Frank D. Eckardt, Dept. Environ. & Geog. Sci., University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
John B. Gates, University of Nebraska-Lincoln
Alfonso F. Davila, Carl Sagan Center at the SETI Institute, 189 Bernardo Ave., Mountain View, CA
Christopher P. McKay, NASA Ames Research Center, Moffett Field, CA
Balaji Rao, Texas Tech University
Ritesh Sevanthi, Texas Tech University
Srinath Rajagopalan, Department of Civil Engineering, SSN College of Engineering, Kalavakkam 603110, India
Nubia Estrada, Texas Tech University
Neil Sturchio, University of Delaware
Paul B. Hatzinger, CB&I Federal Services, Lawrenceville, NJ
Todd A. Anderson, Texas Tech UniversityFollow
Greta Orris, U.S. Geological Survey, Tucson, AZ
Julio Betancourt, U.S. Geological Survey, 431 National Center, Reston, VA
David Stonestrom, U.S. Geological Survey, Menlo Park, CA
Claudio Latorre, Institute of Ecology & Biodiversity (IEB), Santiago, Chile
Yanhe Li, Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
Gregory J. Harvey, USAFSAM/OEC, Wright-Patterson AFB, OH

Date of this Version



Geochimica et Cosmochimica Acta 164 (2015) 502–522


U.S. Government Work


Natural perchlorate (ClO4-) is of increasing interest due to its wide-spread occurrence on Earth and Mars, yet little information exists on the relative abundance of ClO4- compared to other major anions, its stability, or long-term variations in production that may impact the observed distributions. Our objectives were to evaluate the occurrence and fate of ClO4- in groundwater and soils/caliche in arid and semi-arid environments (southwestern United States, southern Africa, United Arab Emirates, China, Antarctica, and Chile) and the relationship of ClO4- to the more well-studied atmospherically deposited anions NO3- and Cl- as a means to understand the prevalent processes that affect the accumulation of these species over various time scales. ClO4- is globally distributed in soil and groundwater in arid and semi-arid regions on Earth at concentrations ranging from 10-1 to 106 µg/kg. Generally, the ClO4- concentration in these regions increases with aridity index, but also depends on the duration of arid conditions. In many arid and semi-arid areas, NO3- and ClO4- co-occur at molar ratios (NO3-/ClO4-) that vary between ~104 and 105. We hypothesize that atmospheric deposition ratios are largely preserved in hyper-arid areas that support little or no biological activity (e.g. plants or bacteria), but can be altered in areas with more active biological processes including N2 fixation, N mineralization, nitrification, denitrification, and microbial ClO4- reduction, as indicated in part by NO3- isotope data. In contrast, much larger ranges of Cl-/ClO4- and Cl-/NO3- ratios indicate Cl- varies independently from both ClO4- and NO3-. The general lack of correlation between Cl- and ClO4- or NO3- implies that Cl- is not a good indicator of co-deposition and should be used with care when interpreting oxyanion cycling in arid systems. The Atacama Desert appears to be unique compared to all other terrestrial locations having a NO3-/ClO4- molar ratio ~103. The relative enrichment in ClO4- compared to Cl- or NO3- and unique isotopic composition of Atacama ClO4- may reflect either additional in-situ production mechanism(s) or higher relative atmospheric production rates in that specific region or in the geological past. Elevated concentrations of ClO4- reported on the surface of Mars, and its enrichment with respect to Cl- and NO3-, could reveal important clues regarding the climatic, hydrologic, and potentially biologic evolution of that planet. Given the highly conserved ratio of NO3-/ClO4- in non-biologically active areas on Earth, it may be possible to use alterations of this ratio as a biomarker on Mars and for interpreting major anion cycles and processes on both Mars and Earth, particularly with respect to the less-conserved NO3- pool terrestrially.