From a modern highly mineralized spring to the Paleoproterozoic ocean: geomicrobiology and isotopic biogeochemistry of the Arvadi spring, Switzerland
Final Report Abstract
Precambrian Earth was the scene for crucial changes in the Earth's atmosphere, hydrosphere and biosphere, and most of the nature of this earliest history of Earth is poorly constrained. While one approach to understand ancient Earth is to identify and interpret the composition of the rock record, another promising way is the analyses of modern model habitats that comprise geochemical settings similar to those presumably found on ancient Earth. The present study provides new data from a modern iron(II)-, sulphide- and O2-rich model habitat about the potential network of iron- and sulphur-metabolizing microorganisms in an ancient ocean undergoing a transition from ferruginous to ferro-euxinic conditions, influenced by the presence of O2 in the water and atmosphere. The Arvadi Spring geochemistry, mineralogy and microbiology was assessed by a set of multidisciplinary techniques including field measurements, wet-chemical analyses, different types of spectroscopy, cultivation- and sequencing-based analyses and controlled growth studies. The Arvadi Spring data imply that the Mesoarchean to early Proterozoic iron- and sulphur-metabolizing microbial community in neritic zones was dominated by microaerophiles and hence supports other studies that suggest microaerophilic iron(II)- and sulphide-oxidizers to have flourished under the slightly oxic conditions in surface waters of the Mesoarchean to Paleoproterozoic ocean. Our results thus provide the possibility to reconstruct depositional environments of iron formations in Mesoarchean and Paleoproterozoic oceans, using S and Fe isotopes - preferably also in combination with Mo isotopes to investigate the effect of Mn-shuttling to the Fe isotopic composition of the deposits. Furthermore, green rust together with ferrihydrite and lepidocrocite were identified as the major mineral phases under the present geochemical framework. Biotic Fe(III) reduction was demonstrated to be organic-limited and to depend partially on contemporaneously ongoing sulfate reduction. Biotic and abiotic Fe(II) oxidation were observed to proceed only at oxygen levels above 0.5%, whereas at 0.5% Fe(III) reduction was sufficient to keep Fe(II) levels at their initial values. Phototrophic and nitrate-reducing Fe(II) oxidation were shown not to contribute to the overall Fe-turnover in the Arvadi Spring. Collectively, the Arvadi Spring helps us to understand ancient Fe-S-cycling from the perspective of a natural environment and enables to expand and strengthen existing, partly vague models of ancient Fe-S-cycling.
Publications
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(2016) Using modern ferruginous habitats to interpret Precambrian banded iron formation deposition. International Journal of Astrobiology FirstView, 1-13
Koeksoy, E., Halama, M., Konhauser, K.O., Kappler, A.
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(2016). Multiple sulfur and oxygen isotopes reveal microbial sulfur cycling in spring waters in the Lower Engadin, Switzerland. Isotopes in Environmental & Health Studies, 52, 75-93
Strauss, H., Chmiel, H., Christ, A., Fugmann, A., Hanselmann, K., Kappler, A., Koniger, P., Lutter, A., Siedenberg, K., Teichert, B.
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(2018) A case study for late Archean and Proterozoic biogeochemical iron- and sulphur cycling in a modern habitat—the Arvadi Spring. Geobiology 16 (4) 353-368
Koeksoy, Elif; Halama, Maximilian; Hagemann, Nikolas; Weigold, Pascal R.; Laufer, Katja; Kleindienst, Sara; Byrne, James M.; Sundman, Anneli; Hanselmann, Kurt; Halevy, Itay; Schoenberg, Ronny; Konhauser, Kurt O.; Kappler, Andreas
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(2018) Modern rather than Mesoarchaean oxidative weathering responsible for the heavy stable Cr isotopic signatures of the 2.95 Ga old Ijzermijn iron formation (South Africa). Geochimica et Cosmochimica Acta
Albut, G., Babechuk, M.G., Kleinhanns, I.C., Benger, M., Beukes, N.J., Steinhilber, B., Smith, A.J.B., Kruger, S.J., Schoenberg, R.
