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AEROBIC Report Summary

Project ID: 337183
Funded under: FP7-IDEAS-ERC
Country: Israel

Mid-Term Report Summary - AEROBIC (Assessing the Effects of Rising O2 on Biogeochemical Cycles: Integrated Laboratory Experiments and Numerical Simulations)

Progress on AEROBiC is occurring on all fronts. In work towards experimentally and theoretically constraining the early S cycle, we combined laboratory experiments of anoxic S species reaction kinetics with models of seawater-sediment interactions and of the global S cycle. This has yielded new and unique insight into the processes of importance in the early S cycle and the isotopic record they have left behind. In work towards similarly constraining the Fe cycle, we combined mineral precipitation experiments with models of the global Fe cycle. This combination has shed light on the processes responsible for generation of banded iron formations, a conspicuous and economically important rock type that formed exclusively in Precambrian times, and a key component of the early Fe cycle until the rise of atmospheric oxygen. In our attempt to better understand proxy records of environmental conditions before and after the rise of atmospheric oxygen, we experimentally investigated the isotopic fractionation of S upon incorporation of sulfate into carbonate minerals. We found appreciable fractionation, especially with decreasing sulfate concentration in the carbonate lattice, with implications for the reconstruction of seawater sulfate isotopic composition from the record of carbonate-associated sulfate (CAS). Work is ongoing to understand the isotopic and trace metal (e.g., Zn, Ni) fingerprint of green rust formation as a possible proxy for Fe chemistry in the early oceans. Finally, in the effort to integrate all of the above knowledge into coupled models of the biogeochemical cycles of redox active elements, we developed a multi-box model of the early marine cycles of S and Fe. In addition to tracking the chemistry of these elements in seawater, the model predicts their concentration and speciation in sediments from various marine depositional environments, thereby allowing direct comparison of model predictions and geologic observations. We have additionally developed a reactive-transport model of sediment diagenesis, into which we embedded a novel model linking cell physiology to S isotope fractionation during microbial sulfate reduction. In aggregate, these models provide important, quantitative constraints on the operation of biogeochemical cycles before and after the rise of atmospheric oxygen.

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