Determining the duration of ridge flank hydrothermal exchange and its role in global biogeochemical cycles

Dr Rosalind Coggon, Prof Damon Teagle, Prof Anthony Koppers (Oregon State)
Rationale: 

Ocean chemistry reflects a dynamic balance between riverine inputs, biological processing, sediment burial, and hydrothermal exchanges with ocean crust. Current models of seawater geochemical evolution generally only consider high temperature hydrothermal venting along ridge axes, ignoring the lower temperature reactions across the vast ridge flanks. Investigating ridge flank exchange, however, is not easy: it requires scientific ocean drilling through thick sediments into the oceanic crust. To date, most investigations have taken place on only young and very old crust. Consequently, although there is a measurable conductive heat flow anomaly in young ocean crust for on average ~65 million years, whether this thermal exchange also results in continual chemical exchange is not known. This project aims to quantify hydrothermal exchange, providing a baseline to investigate vital Earth processes from records of past ocean chemistry. The student will work on the very first samples of 7-63 Ma ocean crust from the Southern Mid-Atlantic Ridge flank that will be collected in spring/summer 2022 by the International Ocean Discovery Program. This will allow the timing and duration of ridge flank hydrothermal exchange to be determined, and consequently its role in setting the chemical composition of the oceans, for the first time.

 

Methodology: 

Low temperature ridge flank flow occurs wherever seawater is able to enter the crust and can continue even if the crust is buried by thick sediment, given sufficiently high crustal permeability. Chemical exchange between the fluid and the ocean crust can be determined from geochemical analyses of representative samples of the different alteration features and their fresh counterparts.  Crucially, the impact of ridge flank hydrothermal exchange on seawater chemistry depends on its duration because the age-area distribution of the ocean crust has varied significantly through the Phanerozoic in response to changing crustal production and subduction rates due to the long-term rearrangement of Earth’s tectonic plates. To quantify ridge flank hydrothermal fluxes the PhD student will:

  1. Determine trace element, major element and isotopic compositions of representative samples from South Atlantic Transect cores.
  2. Determine absolute ages of hydrothermal minerals using a variety of radiometric dating techniques, including: Laser-Ablation MC-ICP-MS U/Pb dating of CaCO3; 87Rb/86Sr dating of clay minerals using TIMS-isotope dilution; and 40Ar/39Ar dating of clay minerals using vacuum encapsulation.
  3. Combine these geochemical analyses with quantitative estimates of the proportions of different alteration features in the cores to quantify hydrothermal exchange across the SAT ridge flank.

 

Location: 
University of Southampton
Training: 

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the National Oceanography Centre Southampton. Specific training will include:

  • Training in state-of-the-art geochemical techniques, including sample preparation, trace element analysis by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and isotope analyses via Thermal Ionization Mass Spectrometry (TIMS).
  • The student will attend the European Petrophysics Consortium/UK-IODP Petrophysics Summer School (University of Leicester), receiving 36 hours of Continuing Professional Development-accredited training and a Techlog Fundamentals training certificate.
  • The student will be part of a world-class team of Integrated Ocean Drilling Program scientists, membership of which is a unique training experience providing opportunities to learn from, be supported by, and develop collaborations within a diverse international research group.
Eligibility & Funding Details: 

Please see https://inspire-dtp.ac.uk/how-apply for details.

Background Reading: 
  • Coggon & Teagle 2011, Hydrothermal calcium-carbonate veins reveal past ocean chemistry. Trends in Analytical Chemistry, vol 30, 1252-1268, doi:10.1016/j.trac.2011.02.011
  • Coggon, R. Christeson, G. Sylvan, J., Teagle, D., Williams, T., and Alvarez Zarikian, C., 2020. Expedition 390/393 Scientific Prospectus. https://doi.org/10.14379/iodp.sp. 390393.2020

 

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