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Estimating Ocean Carbon Uptake from Profiling Float Data

   Ocean and Earth Science

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  Prof T Tyrrell, Prof Minhan Dai, Dr Zhiman Cao, Dr S Hartman  No more applications being accepted  Funded PhD Project (Students Worldwide)

About the Project

Fully-funded PhD open to Chinese nationals.


Project Rationale

Over the last 20 years, understanding of the distributions of heat and salt in the ocean have been transformed by the deployment of several thousand Argo floats, each one equipped with instruments to measure temperature and conductivity (salinity). The last few years have seen the first stage in a next step forward: more than 150 Argo floats were released into the Southern Ocean (SOCCOM programme: with the difference that every float was also equipped with additional sensors to measure pH (used to determine CO2), oxygen, nitrate (nutrient availability) and phytoplankton concentrations. SOCCOM float data has led to new estimates of carbon uptake (first two references). A coordinated international campaign is now underway to equip 1000 Argo floats globally with these additional sensors. Floats have already been deployed in other oceans, as well as the Southern Ocean, and the fleet will become increasingly global over time. US funding has already been announced for half of the fleet.

If this new data resource can be effectively exploited then our understanding of the distribution of carbon in the global ocean could undergo a similar transformation to our understanding of the distributions of heat and salt. However, this advance will only be possible if issues with data quality (existing pH sensors are not all that accurate, alkalinity has to be estimated, and CO2 has to be calculated from pH and alkalinity) can be overcome. This studentship will contribute to efforts to find ways to assess and improve data quality from floats. The results will hopefully lead to a step change in our ability to understand the ocean’s ocean crucial role in absorbing large amounts of CO2 (globally, ocean uptake removes about one quarter of all anthropogenic CO2 emissions).


A recent study (third reference), based on atmospheric data, suggests that current float-based estimates of the CO2 sink for the Southern Ocean may not be accurate. The overall aim of this PhD is to investigate ways of obtaining the highest possible quality surface ocean pCO2 (partial pressure of CO2) estimates from the data collected by biogeochemically-equipped Argo floats. This topic will be addressed through both fieldwork and data analysis, both in Southampton and Xiamen (approximately 1 year of the PhD will be spent in Xiamen, the rest in Southampton). Data analysis will include, for instance: (1) comparison of oxygen and carbon dioxide deviations from saturation (i.e. from equilibrium with the atmosphere; both O2 and CO2 are dissolved gases in seawater, affected by gas exchange across the sea surface), and (2) comparison of surface water deviations to deep water deviations in regions of deep winter mixing. Fieldwork will include, for instance: (1) pH sensor deployment/evaluation, and (2) collection of underway alkalinity data and comparison to coincident algorithm-estimated alkalinity.


All doctoral candidates will enrol in the Graduate School of the National Oceanography Centre, Southampton (GSNOCS), where they will receive specialist training in oral and written presentation skills, have the opportunity to participate in teaching activities, and have access to a full range of research and generic training opportunities. GSNOCS attracts students from all over the world and from all science and engineering backgrounds. There are currently around 150 full- and part-time PhD students enrolled (~60% UK and 40% EU & overseas). Specific training will include:

Depending upon your previous background, training will be provided in data analysis and practical fieldwork techniques as required. You will be trained in computational techniques (the project will probably be carried out mostly in Matlab or Python) and will be encouraged to attend relevant Masters-level courses that are run at Southampton, such as Computational Data Analysis. You will be trained in the collection of oceanographic measurements through involvement in data collection activities at Xiamen and Southampton. You will benefit greatly from interactions with the large numbers of PhD students, PDRAs and academic staff involved in marine biogeochemistry in the research groups at the two universities. Depending on candidate progress and interests, it may be possible to participate in sea-going activity and/or ongoing experimental work on the effect of alkalinity on carbon storage.

Funding Notes

This project is fully funded, including all tuition fees, research costs and an annual stipend of £15,000. Proposed start date: late September, 2022.
Deadline for applications: 30 March, 2022.
For more information about the science or the project, please contact Prof Tyrrell: [Email Address Removed]. For questions about how to apply, visas, and other administrative questions, please contact the GSNOCS office: [Email Address Removed]. For details on how to apply:


A.R. Gray et al. Autonomous biogeochemical floats detect significant carbon dioxide outgassing in the high-latitude Southern Ocean. Geophys. Res. Lett. 45, 9049–9057 (2018).
S.M. Bushinsky et al. Reassessing Southern Ocean air-sea CO2 flux estimates with the addition of biogeochemical float observations. Global Biogeochem. Cycles 33, 1370–1388 (2019).
M.C. Long et al. Strong Southern Ocean carbon uptake evident in airborne observations. Science, 374, 1275-1280 (2021).

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