Sasha Turchyn

Microbially drive iron mineralogy changes in sediment
Lead supervisor: Sasha Turchyn, Department of Earth Sciences
Co-supervisor: Bizhou Zhu, Department of Earth Sciences

Research proposal 

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 beneath certain small ponds 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 and this methane can escape through the rhizosphere and could be emitted to the atmosphere.

We are interested in the salt marsh sediments because they may be a good analogue for sediments that were deposited in oceans early in Earth history and therefore may hold clues for the geochemical and mineralogical signals that we might find in ancient rocks. Throughout the early part of Earth history, all ocean sediments were iron rich.

The student will be involved with collecting sediment core from the North Norfolk Marshes, separating out the layers of sediment and then doing analysis on the sediment mixtures as well as the pore fluids. These analyses will include mineralogical analysis involving X-ray diffraction and infrared spectroscopy (FTIR). The student will be involved with interpreting the IR spectra and understanding how the mineralogy of the sediment is changing. There will be an opportunity to then apply this to literature data of iron minerals extracted from ancient sedimentary rocks to compare one with the other. There may be the opportunity to also do iron speciation and isotope analysis on the various sediment fractions.

Professor Alexandra Turchyn is an environmental and isotope geochemist who studies the carbon cycle in sedimentary environments and across Earth's surface. She has been studying the Norfolk salt marshes as a model ecosystem for over a decade. Bizhou Zhu is a PhD student in the Turchyn lab and will be the day-to-day contact for the student. She is working on iron isotope analysis to understand the mineralogical changes when sediment undergoes diagenetic transformations.