Sasha Turchyn (proposal 2)

Growth of bacteria on iron minerals - impact of carbon source on changing mineralogy
Lead supervisor: Sasha Turchyn, Department of Earth Sciences
Co-supervisor: Bizhou Zhu, Department of Earth Sciences

Research proposal

Life didn't leave a great record of itself early in Earth history. At best we can hope for changes in the chemistry and mineralogy of rocks that we think are indicative of microbial activity. We are currently working in a model ecosystem which we think has similar mineralogy and microbial communities to rocks we find in the geological record. In the North Norfolk salt marshes the sediment is iron-rich and dominated by microbial communities that are reducing the iron while oxidising organic matter. Often there are areas of the salt marsh where the sediment has accumulated an excess of organic matter and the pond has become sulfidic, full of hydrogen sulfide and dominated by microbial sulfate reduction. The pond sediment that has sulfide also has methane.

We have been interested in the changes that happen to sediment when the iron rich mineralogy is exposed to sulfide through a change in microbial community assemblage. We have managed to do this before using a supply of carbon. This process mimics what happens in the real world when iron rich sediments are exposed to sulfide produced through microbial sulfate reduction during burial. This overprinting was likely common and we would like to figure out how we can recognised this microbial overprinting in the geological record.

The student will sample sediment from Norfolk and set up a series of incubations, feeding them different amounts of organic carbon. The student will monitor changes in the fluid chemistry as the cultures grow and then will sample the sediment and analyse the mineralogy and geochemistry of the sediment over time. This will be done using XRD, chemical speciation and Fourier Transform Infrared Spectrometry (FTIR). The equipment is available either in Earth Sciences or the Turchyn lab.

This project is linked to the other project in Norfolk and the students can work in parallel.

Professor Alexandra (Sasha) Turchyn is an environmental and isotope geochemist who studies sediment biogeochemistry. Bizhou Zhu is a PhD student in her group who will help supervise the day to day.