Iron cycling in the anoxic cryo-ecosystem of Antarctic Lake Vida

Iron redox cycling in metal-rich, hypersaline, anoxic brines plays a central role in the biogeochemical evolution of life on Earth, and similar brines with the potential to harbor life are thought to exist elsewhere in the solar system. To investigate iron biogeochemical cycling in a terrestrial analog we determined the iron redox chemistry and isotopic signatures in the cryoencapsulated liquid brines found in frozen Lake Vida, East Antarctica. We used both in situ voltammetry and the spectrophotometric ferrozine method to determine iron speciation in Lake Vida brine (LVBr). Our results show that iron speciation in the anoxic LVBr was, unexpectedly, not free Fe(II). Iron isotope analysis revealed highly depleted values of -2.5% for the ferric iron of LVBr that are similar to iron isotopic signatures of Fe(II) produced by dissimilatory iron reduction. The presence of Fe(III) in LVBr therefore indicates dynamic iron redox cycling beyond iron reduction. Furthermore, extremely low dO–SO4 2values (-9.7%) support microbial iron-sulfur cycling reactions. In combination with evidence for chemodenitrification resulting in iron oxidation, we conclude that coupled Responsible Editor: Stuart Grandy. Electronic supplementary material The online version of this article (doi:10.1007/s10533-017-0346-5) contains supplementary material, which is available to authorized users. B. C. Proemse School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia A. E. Murray (&) Division of Earth and Ecosystem Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, USA e-mail: [email protected] C. Schallenberg School of Earth and Ocean Sciences, University of Victoria, PO Box 1700 Stn CSC, Victoria, BC V8W 2Y2, Canada C. Schallenberg A. R. Bowie Antarctic Climate and Ecosystems CRC, and Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 80, Hobart, TAS 7001, Australia B. McKiernan M. E. Wieser Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada B. T. Glazer Department of Oceanography, University of Hawaii, 1000 Pope Rd, Honolulu, HI 96822, USA S. A. Young Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, FL 32306, USA N. E. Ostrom Department of Integrative Biology and DOE Great Lakes Bioenergy Research Center, Michigan State University, 288 Farm Lane, East Lansing, MI 48824-5633, USA