PhD position in Marine Microbial Biogeochemistry

PhD position in Marine Microbial Biogeochemistry

Position: PhD position in Marine Microbial Biogeochemistry
Employer: School of Ocean and Earth Sciences, University of Southampton
Location: Southampton, United Kingdom
Type: Full time
Level: Student / Graduate
Salary: Open
Education required: Undergraduate degree
Final date to receive applications: 8 January 2026
Posted: 20 November 2025

PhD position – Unravelling the Mystery of Mesopelagic Carbon Cycling by Microbes – University of Southampton, UK.

Marine microbes are key drivers of biogeochemical cycling. Assessment of their activities, so far mostly done by shipboard incubations, are prone to artefacts from inevitable changes in incubation conditions. This project utilizes a novel technology to capture microbial activities in situ to tackle critical questions on carbon‑cycling in the mesopelagic ocean.

Marine microbes in the ‘twilight’ (or mesopelagic) ocean exert critical controls on the ocean’s ability to sequester atmospheric CO₂ into the ocean interior. Some respire and thereby remove most organic carbon escaping the sunlit ocean preventing it from reaching the deep; while others perform dark CO₂‑fixation (chemo synthesis) to replenish the organic carbon pool. Mysteriously, while diagnostic genes for biochemical pathways fuelling chemo synthesis can be highly abundant, the chemical substrates required to drive these pathways are at vanishingly low concentrations in the mesopelagic.

Meanwhile, we still do not have a good handle on the true microbial respiration rates (CO₂ production and oxygen consumption) in these waters, with estimates so far ranging across orders of magnitude. A possible reason for the disconnects is that microbial processes have mostly been assessed via shipboard incubations that are prone to artefacts. This project will use a newly‑developed In situ Incubation and Filtration System (InSIncFS) to capture the true, in‑situ microbial activities by incubating under the temperature and pressure conditions that microbes experience.

The candidate will lead the testing of the novel equipment through field trials and laboratory tests, integrating biogeochemistry and microbial analysis, to compare biological rates in‑situ under pressure conditions vs ex‑situ in non‑pressurised conditions. The transformative project will deliver a first‑of‑its‑kind reassessment of key processes in carbon cycling in a critical zone of the ocean, capturing the true modes and magnitudes of these fluxes in situ that were impossible before.

• Deployment and maintenance of the InSIncFS system
• Microbial activity measurements on shipboard and in laboratories
• Experimental design, stable isotope analyses
• Molecular sampling, omics and bioinformatic analyses
• Transferable skills: communication, publication, management, teamwork and leadership
• Join a multidisciplinary research team within the UoS Marine Biogeochemistry Research Group, NOC Ocean Biogeosciences, and Ocean Technology and Engineering Groups, exposure to a variety of biogeochemical and molecular techniques, engineering support, and data integration and interpretation
• Must have an aptitude for practical fieldwork at sea
• Opportunities to attend and present results at international conferences are strongly encouraged

All applications for the IGNITE Doctoral Landscape Award should be submitted by 11:59pm on Thursday 8 January 2026. Use the following link to apply for the full‑time or part‑time programme. For project inquiry, contact Phyllis Lam (). We advise you to contact the lead supervisor of a project to discuss the project and check your suitability before submitting an application. You are strongly advised to apply for one project so that you can tailor your application to the project, but you can apply for a maximum of two projects.

Both UK and international students are eligible to apply for an IGNITE award. However, NERC stipulates that a maximum of 30% of IGNITE studentships (usually 5 studentships per year) can be provided to international applicants, so competition for these studentships is very high. We welcome applications from…