School of Ocean and Earth Sciences, University of Southampton

Homepage: https://www.southampton.ac.uk/oes

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

Project Overview:

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.

Project Description:

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; whilst others perform dark CO2-fixation (‘chemosynthesis’ – CO2 fixed into biomass without light) to replenish the organic carbon pool. Mysteriously, while diagnostic genes for biochemical pathways fuelling chemosynthesis 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 magnitudes. 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 utilize 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 with 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-pressurized conditions. This 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.

This project will be located in Southampton.

Training:

The IGNITE 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.

* 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. The student will join a multidisciplinary research team within the UoS Marine Biogeochemistry Research Group, NOC Ocean Biogeosciences, and Ocean Technology and Engineering Groups, with exposure to a variety of biogeochemical and molecular techniques, engineering support, and know-how’s on data integration and interpretation. The student must have an aptitude for practical fieldwork at sea. Opportunities to attend and present results at inter/national conferences are strongly encouraged.

All applications to the IGNITE Doctoral Landscape Award should be submitted by 11:59pm on Thursday 8th January 2026. Please use the following link to apply for either the full time or part time programme:

Full time

Part time

For project inquiry, please contact Phyllis Lam (P.Lam@southampton.ac.uk). 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 applicants from a diverse range of backgrounds but recognise systemic barriers to entry into postgraduate research for certain groups. To support this, IGNITE has an opt-in guaranteed interview scheme for qualifying UK applicants who self-identify as racially minoritised (i.e., come from a Black, Asian or minority ethnic background). Please contact nerc-dla@soton.ac.uk once you have submitted a complete application to opt into this scheme.

IGNITE DLA Webinar

Watch the IGNITE Doctoral Landscape Award webinar here. Find out more about the IGNITE DLA programme, the application process and what happens if you are shortlisted for interview.

Funding Notes

The IGNITE Doctoral Landscape Award funds PhD researchers for 3.5 years, full- or part-time. An IGNITE DLA studentship includes a tax-free stipend at the UKRI standard rate (£20,780 for the academic year 2025/26). Funding covers Home tuition fees; the difference between Home and International tuition fees will be waived by the University. The IGNITE DLA provides a Research Training Support Grant of £2200 per year (£7700 across the 3.5 years) to be used on small project costs, conference attendance and individual training needs.