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


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


Project Description


Dr Uwe Balthasar, University of Plymouth – Contact me

Dr Vassilis Kitidis, Plymouth Marine Laboratory

Mrs Marie Palmer, University of Plymouth

Dr Simon Ussher, University of Plymouth

Scientific Background

The natural weathering of calcium (Ca) and magnesium (Mg) 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 due to the effects on their skeletal secretion [1-2]. The recent global development of ocean alkalinity enhancement (OAE), a carbon dioxide removal (CDR) method by which Ca- and/or Mg-rich rock powders are added to seawater to convert dissolved CO2 into bicarbonate or carbonic acid [3], has the potential to dramatically accelerate the changes to Ca2+ and Mg2+ 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 Ca and Mg concentrations 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 Mg2+ and Ca2+ over ecological time scales. The results will help to mitigate and environmental impact of OAE.

Research Methodology

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 (Python, R, Matlab).

Person Specification

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


  • 1 Balthasar, U. & Cusack, M., 2015. Aragonite-Calcite seas – Quantifying the gray area. Geology, 43(2), 99-102;
  • 2 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;, 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;
  • 3 National Academies of Sciences, Engineering, and Medicine, 2022, A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. Washington, DC: The National Academies Press, pp. 323.
  • 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;
  • 5 Lebrato, M., et al., 2020, Global variability in seawater Mg:Ca and Sr:Ca ratios in the modern ocean. PNAS, 117 (36), 22281–22292;

Key Information

  • This project has been shortlisted for funding by the ARIES NERC DTP and will start on 1st October 2024. The closing date for applications is 23:59 on 10th January 2024.
  • Successful candidates who meet UKRI’s eligibility criteria will be awarded a NERC studentship, which covers fees, stipend (£18,622 p.a. for 2023/24) and research funding. International applicants are eligible for fully-funded ARIES studentships including fees. Please note however that ARIES funding does not cover additional costs associated with relocation to, and living in, the UK. We expect to award between 4 and 6 studentships to international candidates in 2024.
  • ARIES students benefit from bespoke graduate training and ARIES provides £2,500 to every student for access to external training, travel and conferences, on top of all Research Costs associated with the project. Excellent applicants from quantitative disciplines with limited experience in environmental sciences may be considered for an additional 3-month stipend to take advanced-level courses.
  • ARIES is committed to equality, diversity, widening participation and inclusion in all areas of its operation. We encourage enquiries and applications from all sections of the community regardless of gender, ethnicity, disability, age, sexual orientation and transgender status. Academic qualifications are considered alongside non-academic experience, and our recruitment process considers potential with the same weighting as past experience.
  • All ARIES studentships may be undertaken on a part-time or full-time basis, visa requirements notwithstanding.
  • For further information, please contact the supervisor. To apply for this Studentship follow the instructions at the bottom of the page or click the 'apply now' link.
  • ARIES is required by our funders to collect Equality and Diversity Information from all of our applicants. The information you provide will be used solely for monitoring and statistical purposes; it will remain confidential, and will be stored on the UEA sharepoint server. Data will not be shared with those involved in making decisions on the award of Studentships, and will have no influence on the success of your application. It will only be shared outside of this group in an anonymised and aggregated form. You will be ask to complete the form by the University to which you apply.
  • ARIES funding is subject to UKRI terms and conditions. Postgraduate Researchers are expected to live within reasonable distance of their host organisation for the duration of their studentship. See for more information

Applications open

Click this link to apply to University of Plymouth