Mg2+ and Ca2+ variability in seawater and the impact on marine calcifiers

Director of Studies: Dr Uwe Balthasar

2^nd Supervisor: Dr Vassilis Kitidis

3^rd Supervisor: Dr Simon Ussher

4^th Supervisor: Dr Tracy Aze  

Applications are invited for a 3.5 years PhD studentship. The studentship will start on 1 October 2025.

Scientific background: 

The natural weathering of calcium and magnesium rich minerals and rocks over geological time scales, controls the bulk chemical composition and pH of seawater and influenced the ecological success of marine calcifiers over millions of years [1-2]. The recent global development of ocean alkalinity enhancement (OAE), a carbon dioxide removal (CDR) method by which rock powders are added to seawater [3], has the potential to dramatically accelerate the changes to calcium and magnesium in coastal seas with possibly significant impacts on marine calcifiers [4]. To assess these possible impacts, we need to improve our understanding of the natural variability of the concentrations of calcium and magnesium in seawater [5] and how expected changes of these will impact marine calcifiers. The successful candidate for this project will work in the natural laboratory of Plymouth Sound to establish the first baseline of the natural variability of magnesium and calcium over ecological time scales. The results will help to mitigate the environmental impact of OAE.

This studentship will take advantage of world leading research vessels and facilities at the Western Channel Observatory and the University of Plymouth (UoP). Water samples from Plymouth Sound will be regularly sampled and analysed for Mg2+, Ca2+, pH, DIC, alkalinity, and salinity at the Plymouth Marine Laboratory and the UoP. Alongside this, bivalves will be cultured at the aquaculture facilities at the UoP at various Mg/Ca ratios and analysed for oxygen consumption, tissue growth and shell secretion.

You will receive training in oceanographic surveys, marine sampling, sensor deployment, and the analysis of dissolved inorganic carbon and alkalinity, marine aquaculture, electron microscopy, and to work in ISO 9001 certified laboratories. You will gain expertise in analytical techniques for elemental analysis such as Inductively Coupled Plasma- Atomic Emission Spectroscopy, and data analysis and programming skills (e.g. Python, R, Matlab).

Suited for applicants with a degree in an Earth, environmental, chemistry or biological science subject and a passion for multidisciplinary environmental and biological research. 

Balthasar, U. & Cusack, M., 2015. Aragonite-Calcite seas – Quantifying the gray area. Geology, 43(2), 99-102; https://doi.org/10.1130/G36293.1

Eichenseer, K., Balthasar, U., Smart, C., Stander, J., Haaga, K., and Kiessling, W., 2019. Jurassic shift from abiotic to biotic control on marine ecological success. Nature Geoscience, 12, 638–642; https://doi.org/10.1038/s41561-019-0392-9.

Kitidis, V., et al., 2024. Magnesium hydroxide addition reduces aqueous carbon dioxide in wastewater discharged to the ocean. Communications Earth & Environment, 5, 354; https://www.nature.com/articles/s43247-024-01506-4

Ries, J. B., 2010, Review: geological and experimental evidence for secular variation in seawater Mg/Ca (calcite-aragonite seas) and its effects on marine biological calcification. Biogeosciences, 7, 2795–2849; www.biogeosciences.net/7/2795/2010

Lebrato, M., et al., 2020, Global variability in seawater Mg:Ca and Sr:Ca ratios in the modern ocean. PNAS, 117 (36), 22281–22292; www.pnas.org/cgi/doi/10.1073/pnas.1918943117  

Applicants should have a first or upper second class honours degree in Earth, Environmental, Biological Science, Chemistry or a relevant Masters qualification.

If your first language is not English, you will need to meet the minimum English requirements for the programme, IELTS Academic score of 6.5 (with no less than 5.5 in each component test area) or equivalent.

Successful candidates who meet UKRI’s eligibility criteria will be awarded a fully-funded ARIES studentship of fees, maintenance stipend (£19,237 p.a. for 2024/25) and research costs.

A limited number of ARIES studentships are available to International applicants. Please note however that ARIES funding does not cover additional costs associated with relocation to, and living in, the UK. 

NB: The studentship is supported for 3.5 years of the four-year registration period. The subsequent 6 months of registration is a self-funded ‘writing-up’ period. 

ARIES is committed to equality, diversity, widening participation and inclusion in all areas of its operation. We encourage applications from all sections of the community regardless of gender, ethnicity, disability, age, sexual orientation, and transgender status. Projects have been developed with consideration of a safe, inclusive, and appropriate research and fieldwork environment. Academic qualifications are considered alongside non-academic experience, with equal weighting given to experience and potential. 

For further information, please visit www.aries-dtp.ac.uk.

If you wish to discuss this project further informally, please contact Dr Uwe Balthasar .

Please see our apply for a postgraduate research programme webpage for a list of supporting documents to upload with your application. 

For more information on the admissions process generally, please contact research.degree.admissions@plymouth.ac.uk. 

The closing date for applications is 8 January 2025. Shortlisted candidates will be invited for interview after the deadline. We regret that we may not be able to respond to all applications.  Applicants who have not received a response within six weeks of the closing date should consider their application has been unsuccessful on this occasion.