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K.G. Jebsen Centre for Deep Sea Research

Investigating multiple sulfur isotope variations in active hydrothermal chimneys and fluids from the Arctic Mid Ocean Ridge

MSc project of Lotte Johannessen

Project title

Investigating multiple sulfur isotope variations in active hydrothermal chimneys and fluids from the Arctic Mid Ocean Ridge

Supervisors

Desiree Roerdink, Eoghan Reeves, John Jamieson (Memorial University of Newfoundland, Canada)

Project description

Multiple sulfur isotopes (32S, 33S, 34S, 36S) can provide valuable insights into deep-sea hydrothermal processes. The isotopic composition of hydrothermal fluids, sulfate and sulfide minerals depends on relative contributions from different sulfur sources and fractionation processes happening below or at the seafloor. Abiotic sulfur sources include seawater sulfate, magmatic sulfur and sulfur leached from basaltic host rocks or sediments, each of which has a distinct isotopic composition. Fractionation of major (δ34S) and minor (δ33S, δ36S) sulfur isotopes occurs by chemical reactions such as thermochemical reduction of sulfate to sulfide, precipitation of anhydrite above 150°C and fluid-rock interactions. Biological processes such as microbial sulfate reduction are generally less important in high-temperature systems, but can generate isotope effects at the seafloor or indirectly affect fluid isotopic compositions when biogenic sulfide is leached at depth.

This project will investigate the variations in multiple sulfur isotope ratios in hydrothermal fluids and sulfate and sulfide minerals from active chimneys in vent fields along the Arctic Mid Ocean Ridge (AMOR). It aims to explore the extent to which variations in the AMOR hydrothermal systems (magmatic input, sedimentary input, host rocks, fluid temperature and depth) are reflected in sulfur isotope ratios, and increase our understanding of hydrothermal sulfur cycling along this ridge segment. The project is part of ongoing stable isotope studies (Fe and Cu) at the K.G. Jebsen Centre for Deep Sea Research.