Ocean circulation and the Southern Ocean carbon sink

Dr Kevin Oliver, Dr Nathan Briggs, Dr Bieito Fernández Castro, UoS; Dr Jonathan Lauderdale, Massachusetts Institute of Technology

Increasing atmospheric CO2 is partly mitigated by uptake of excess carbon by the ocean, but there is also a large natural ocean-atmosphere carbon cycle which is also vulnerable to change. Carbon is removed from the surface ocean – and therefore the atmosphere – in sinking organic matter, is remineralised (returned to inorganic form) in the subsurface ocean, and is returned to the surface by the circulation. The Southern Ocean is a hub in the global carbon cycle, partly due to its large vertical exchanges, which have a complex structure (Figure 1). A critical question is: “how much remineralisation occurs in waters that are quickly returned to the surface, versus waters that remain isolated from the atmosphere for centuries?”, yet there are large uncertainties in the structure both of the circulation and of remineralisation. This project will seek to answer this question by combining a novel dataset for observing the biological pump (Briggs et al., 2020) with recent modelling advances (Lauderdale & Cael, 2021) in understanding the link between circulation, remineralisation, and the Southern Ocean carbon sink.



The principal scientific tool used in the project will be the ocean general circulation model MITgcm. A significant component of the project will be the analysis of observational data from Biogeochemical-Argo floats (Briggs et al., 2020).  This will be used in combination with existing output from the model (Lauderdale & Cael, 2021) to inform new simulations. The main project outputs are biogeochemical, but the day-to-day work will often be focused on ocean circulation and its underlying physics. The steps are:


  1. Use Biogeochemical-Argo observations (Briggs et al., 2020) of sinking organic matter and dissolved oxygen to estimate the structure of remineralisation. Optionally, the student may examine the validity of extending this dataset to the much larger number of Argo floats with oxygen data only.
  2. Examine the Lauderdale & Cael (2021) simulations, which explored the relationship between remineralisation and the carbon sink, to assess the relationship with Argo-observable quantities.
  3. Design and analyse new simulations which: (a) implement the findings from Step 2; (b) explore the sensitivity of the ocean carbon sink to regional changes in the remineralization, distribution and processes which modify the Southern Ocean circulation, such as surface winds and mixing along and across surfaces of constant density.



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 based at the National Oceanography Centre Southampton. Specific training will include:

  • Numerical modelling and use of high-performance computing.
  • Analysis of large modelling and observational datasets.
  • Combined use of models and observations to develop and test hypotheses.
  • Understanding of ocean circulation and the carbon cycle.
  • Opportunities to attend national/international conferences to disseminate the candidate’s results and to broaden their scientific network.
  • Opportunities to visit co-supervisor at MIT (USA).

There is no fieldwork tied to the project. Students lead-supervised by Oliver have been able to participate in a research cruise if they chose to, but this is not guaranteed.

Eligibility & Funding Details: 

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


Background Reading: 

[1] Briggs, N., Dall’Olmo, G., & Claustre, H. (2020). Major role of particle fragmentation in regulating biological sequestration of CO2 by the oceans. Science, 367 (6479). 791-793. https://doi.org/10.1126/science.aay1790

[2] Lauderdale, J. M., & Cael, B. B. (2021). Impact of remineralization profile shape on the air-sea carbon balance. Geophysical Research Letters, 48(7), e2020GL091746. https://doi.org/10.1029/2020GL091746