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K.G. Jebsen Centre for Deep Sea Research

Detecting microbial sulfate reduction coupled to anaerobic methane oxidation in hydrothermal sediments with stable isotopes (S, Fe) and trace elements

MSc project of Karen Moltubakk

Project title

Detecting microbial sulfate reduction coupled to anaerobic methane oxidation in hydrothermal sediments with stable isotopes (S, Fe) and trace elements

Supervisors

Desiree Roerdink, Francesca Vulcano, Ida Helene Steen, Harald Strauss (University of Münster, Germany)

Project description

Microbial sulfate reduction was probably one of the earliest metabolisms to evolve on Earth and it represents an important component of the modern marine and terrestrial carbon cycle. The presence and activity of sulfate reducers in modern sediments can be detected using molecular biology techniques, geochemical analyses of pore fluids, rate measurements using radioactive sulfate, and stable isotopes measured in sulfide minerals that are produced by sulfate reduction. However, the detection of past microbial activity in the older rock record is more complicated and requires robust tracers for microbial sulfate reduction, that ideally also provide information on the type of electron donors (molecular hydrogen, organic matter or methane) used by ancient sulfate reducers.

Recent work has suggested that a combination of stable sulfur (S) isotopes, iron (Fe) isotopes and trace elements measured in pyrite from methane seep sediments can be used to identify microbial sulfate reduction coupled to anaerobic methane (CH4) oxidation (AOM), a process that involves an association between sulfate reducers and anaerobic methanotrophs (ANME). Identifying this specific pathway is important for our understanding of carbon cycling in the present and past. In this project, we will test the use of the recently proposed proxy for SRB-AOM in anoxic hydrothermal sediments, which represent a different type of environment than methane seeps and may be more representative of settings on the early Earth.