How does seawater composition influence calcification in marine calcifiers?_REP2025

Project background

The skeletons of marine calcifiers are composed of aragonite and/or calcite, the primary minerals of calcium carbonate. Aragonite is typically more soluble than calcite, making the mineral composition of organisms’ skeletal structures a key factor in their response to ocean acidification. One of the main determinants of the mineral form of calcium carbonate is the Mg/Ca ratio in the surrounding solution during formation. Magnesium ions (Mg²⁺) act as a growth inhibitor for calcite, replacing calcium ions (Ca²⁺) within its crystal structure, a substitution that does not occur in aragonite. This incorporation of magnesium reduces the stability of calcite crystals, and the process is temperature-dependent, which is why the magnesium content in calcite can be used as a paleothermometer. Both Mg²⁺ and Ca²⁺ are among the most abundant cations in seawater, and their concentrations are influenced by slow geological processes, such as mid-ocean ridge activity and continental weathering (via river runoff). While the concentrations of Mg²⁺ and Ca²⁺ in global seawater change gradually over geological time scales, their fluctuations over millions of years are linked to shifts in the skeletal mineralogy of marine calcifiers.

In contrast to open ocean seawater, which has an average Mg/Ca ratio of 5.2, the Mg/Ca ratio in coastal waters can vary significantly, especially near rivers, where it is typically much lower. Preliminary data from Plymouth Sound indicate that the Mg/Ca ratio fluctuates between 5.5 and 4 over just a few days—equivalent to more than 10 million years of change in bulk ocean water. Plymouth Sound therefore serves as an excellent natural laboratory to explore the impact of seawater Mg/Ca variation on the mineral composition of calcifiers and the incorporation of magnesium into calcite.

In this project, you will collect seawater and intertidal calcifying organisms from shoreline locations along a transect extending farther from the influence of the Tamar River. Seawater samples will be analysed for major cations, while invertebrate calcite will be examined for magnesium content and the proportion of aragonite to calcite in the shells (for taxa that secrete both minerals). The results will shed light on how natural variation in seawater composition affects the skeletal structure of calcifiers, with potential implications for their vulnerability to ocean acidification. Additionally, understanding the variability of magnesium content in biomineralized calcite from coastal ecosystems will enhance the reliability of Mg-based thermometry for coastal species.

Eligibilty criteria

Students must meet all of the eligibility requirements listed below to apply for a REP:

Be undertaking their first undergraduate degree studies (or integrated Masters) – note that students in in their final year who have graduated and no longer have student status at the time the placement starts are not eligible;
Be eligible for subsequent NERC PhD funding (please see the relevant text in the Terms and conditions for training funding and associated guidance for further information); and
have the right to work in the UK.

Students from outside the UK who do not already have right to work in the UK, should not apply.

How to apply

The deadline for applications will be 12:00 on Monday 19 May 2025.

In order to be considered for a placement, please apply to aries.dtp@uea.ac.uk providing the following:

A supporting statement explaining your motivation for applying for this project. Please include answers to the following questions:
- which project are you applying for?
- why have you applied for this project (e.g. what interested you about this project, what in particular made you want to undertake this research)?
- what do you hope to achieve by undertaking this placement (e.g. is it for experience, to gain skills, to develop your interests)?
- what skills do you have that make you an ideal candidate for this placement (e.g. what skills have you developed during your degree that might apply)?
- what do you hope to do when you complete your degree (e.g. have you considered a working in scientific research in the future, or is this your first experience)?
A recent CV
A reference from your personal tutor (please ask your tutor to send this to us directly)
An interim transcript if available
Please also complete the online EDI form (this form is a mandatory part of the application process, but contains ‘prefer not to say’ options for all questions asked)

Selection process

· Applications are screened for eligibility

· Applications are forwarded to supervisors (the EDI form is not included)

· Supervisors shortlist candidates and interview for the placement.

Candidates will be scored according to the following criteria:

Fit to project (e.g. your current skills, area of study, interests)
Enthusiasm for environmental research (e.g. what you hope to achieve through undertaking this placement, why you chose this project in particular)
Evidence of suitability to undertake a research placement (e.g. evidence from your tutor reference, transcript, and CV that you are an engaged student)

Successful candidates will be informed by Friday 13^th June 2025