期刊
BIOGEOCHEMISTRY
卷 134, 期 1-2, 页码 17-27出版社
SPRINGER
DOI: 10.1007/s10533-017-0346-5
关键词
McMurdo dry valleys; Lake Vida; Iron; Redox
资金
- National Science Foundation [ANT-0739681, ANT-0739698]
- NSF Geobiology and Low Temperature Geochemistry program [1053432, 1348935]
- DOE Great Lakes Bioenergy Research Center (DOE Office of Science) [BER DE-FCO2-07ER64494]
- NASA-NASA Astrobiology Institutes Icy Worlds
- Water and Astrobiology at the University of Hawaii
- National Science Foundation McMurdo LTER Award [ANT-1041742]
- Division Of Earth Sciences
- Directorate For Geosciences [1456430] Funding Source: National Science Foundation
- Division Of Earth Sciences
- Directorate For Geosciences [1053432, 1348935] Funding Source: National Science Foundation
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 -2.5aEuro degrees 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 delta O-18-SO4 (2-) values (-9.7aEuro degrees) support microbial iron-sulfur cycling reactions. In combination with evidence for chemodenitrification resulting in iron oxidation, we conclude that coupled abiotic and biotic redox reactions are driving the iron cycle in Lake Vida brine. Our findings challenge the current state of knowledge of anoxic brine chemistry and may serve as an analogue for icy brines found in the outer reaches of the solar system.
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