Biogeochemistry of hydrothermal systems in the Scotia Sea

Abstract

Submarine hot springs play an important role in global heat transfer; element cycling; economic ore deposition; and as an energy source for chemosynthetic ecosystems. Almost four decades of deep-sea exploration have revealed hydrothermal venting to be a ubiquitous phenomenon across the global ocean floor, yet these systems have only recently been discovered in Antarctica. Between 1998 and 2012, high-temperature vents were detected and sampled along the East Scotia Ridge (ESR) and within the Kemp Caldera, which forms part of the South Sandwich island arc, during four research cruises to the Scotia Sea. These vent sites are the first discovered south of the polar front, and they have a distinct faunal assemblage that has characterised them as a new biogeographic province. In this thesis, I investigate the controls on hydrothermal fluid chemistry at the ESR and the Kemp Caldera, using the rare earth elements (REEs) as geochemical tracers. I demonstrate that REE distributions in hydrothermal fluids and associated sulphate deposits are variably influenced by reaction with the host rock; temperature and phase separation; fluid composition and magmatic gas injection; and anhydrite precipitation/dissolution. Secondly, I assess tissue bioaccumulation of metals in Kiwa tyleri sp. nov., the dominant macrofaunal species at the ESR vent sites, in response to their environmental exposure. Significant variation in metal burden between tissues reflects both abiotic and biotic controls on metal uptake, including external concentration; trophic position; ecological niche and behavioural traits; in addition to cellular mechanisms of regulation. Finally, I investigate proteomic pathways of metal regulation in the shallow water mussel, Mytilus edulis, and the vent-living mussel, Bathymodiolus sp. I show that both species have strong defence mechanisms against metal toxicity and oxidative stress, which may be important for successful colonisation of hydrothermal systems. This work highlights the diversity in chemical compositions of fluids venting in back-arc and island-arc settings, and provides an insight into metal regulatory mechanisms that may have facilitated faunal colonisation of these extreme habitats.

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ORCID for Rachael H. James: orcid.org/0000-0001-7402-2315

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