Dynamics, instability and tracer spreading in a hydrothermal plume


  • Supervisors: Prof. Ric Williams, University of Liverpool
    Alessandro Tagliabue, University of Liverpool


  • External Supervisors: Dr Carl Spingys (University of Southampton)
    Prof Alberto Naveira Garabato (University of Southampton)
  • Contact:

    Prof. Ric Williams (University of Liverpool), ric@liv.ac.uk

  • CASE Partner:

Application deadline: 10 January 2020

Introduction:

Hydrothermal plumes provide important inputs of trace metals into the deep ocean and these trace metals are often used as tracers of plume dispersion. We know very little about the mechanisms by which these tracers, that are essential for life in the oceans, spread from the hydrothermal plume into the ocean interior and ultimately the upper ocean environment to support primary productivity. 

Hydrothermal vents occur all along ocean tectonic plate margins and they generate warm, buoyant fluid at the sea floor. The buoyant fluid rises in narrow plumes which have a horizontal scale of the order of 100m --- looking much like smoke from an industrial chimney rising in the atmosphere. The buoyant fluid eventually reaches a neutrally buoyant level, approximately 200-500m above the sea floor, and then spreads horizontally. The horizontal spreading is affected by rotation on a horizontal scale of several kilometres, leading to closed horizontal recirculation around the buoyant plume. The tracers entrained in the plume can only spread further horizontally through instability processes or topographic interactions. This PhD project will provide understanding on the control of these instability processes and topographic interactions, and their effect on tracer distributions, using a combination of new field data and high-resolution modeling in idealised configurations. These new insights will transform our understanding of how metals in hydrothermal vents are dispersed throughout the ocean interior. 

At the start of 2018 we measured the physical and biogeochemical characteristics of the hydrothermal plumes above three different vent sites along the mid-Atlantic ridge: Lucky Strike, Rainbow and TAG. These observations included high horizontal resolution tow-yo sections (Fig. 1 & 2) through the plume at each site. In addition, turbulence microstructure instruments were deployed to gain understanding of mixing on the centimeter scale. These new data will provide a unique opportunity to generate new knowledge about the horizontal structure and lateral processes controlling spreading in these environments.

Project Summary:

Our aim is to understand how the plume dynamics operate on the fine scale of several hundreds of metres to kilometres close to topography, and the physical mechanisms affecting the dispersal of trace metals from the vent. The student will explore the following work plan:

  • A synthesis of all of the CTD and tow-yo data will be conducted to provide a time history of the plume evolution and to allow a connection to the available tracer data to be made;
  • An instability analysis for the plume will be extended using a combination of hydrographic and velocity data to identify the nature of the instabilities leading to the tracer dispersion;
  • A high resolution non-hydrostatic circulation model will be applied to examine the evolution of a modelled plume in an idealised domain and identify the processes that affect its tracer dispersion for a variety of topography domains;
  • The student will finally explore how this plume-based view of a hydrothermal vent is reconciled with the larger-scale tracer data.

There will be an opportunity for the student to refine the workplan as the project progresses, modifying the priorities according to the signals emerging from this combined observational and modelling study.

References:

Papers relevant to the work plan: 

Speer, K and Marshall, J (1995). The growth of convective plumes at seafloor hot springs. J. Mar. Res.,  53, 1025-1057. 

Speer, K and Helfrich K. (1995) Hydrothermal plumes: a review of flow and fluxes. Hydrothermal Vents and Processes 87:373-385 

Naveira Garabato, A. C., Forryan, A., Dutrieux, P., Brannigan, L., Biddle, L. C., Heywood, K. J., ... Kimura, S. (2017). Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf. Nature, 542(7640), 219-222. 

Papers relevant to the context of the study: 

German, C. R., A. M. Thurnherr, J. Knoery, J. L. Charlou, P. Jean-Baptiste and H.

N. Edmonds, 2009: Heat, volume and chemical fluxes from submarine venting: A synthesis of results from the Rainbow hydrothermal field, 36 degrees N MAR. Geochimica Et Cosmochimica Acta, 73(13): A428-A428. 

Lough, A.J.M … R.A. Mills (2017). Opposing authigenic controls on the isotopic signature of dissolved iron in hydrothermal plumes. Geochimica Et Cosmochimica Acta, 202, 1-20. 

Thurnherr, A. M. , G. Reverdin, P. Bouruet-Aubertot, L. C. St Laurent, A. Vangriesheim and V. Ballu, 2008: Hydrography and flow in the Lucky Strike segment of the Mid-Atlantic Ridge. Journal of Marine Research, 66: 347-372

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