Hot Rocks: Calcium carbonate production in a warming ocean

   School of Energy, Geoscience, Infrastructure and Society

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  Dr A Poulton  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

Fully funded PhD position available to UK and international students! Apply by 12 noon, 5 January 2024 (international applicants must have contacted supervisor by 11 December 2023).

The ocean is warming at an alarming rate, having absorbed around 90% of the excess heat caused by atmospheric warming. How ocean biology responds to this rapid warming is a major research question, with many species shifting their spatial distributions and biogeography, as well as undergoing radical changes to their metabolism and trophic interactions. The impact of these biogeographical and physiological changes to ocean biogeochemistry are poorly understood, though gaining such understanding is crucial for future predictions due to the strong feedback between the marine carbon cycle and climate.

Coccolithophores, with their cellular production of calcium carbonate, are an important component of the marine carbon cycle and their growth provides a negative feedback to oceanic carbon dioxide uptake through their influence on seawater alkalinity. One of the key calcifying coccolithophore species, Emiliania huxleyi, exists in the ocean as morphometrically distinct ‘ecotypes’ (Fig. 1). These different ‘morphotypes’ are hypothesized to have different biogeographical ranges and environmental niches; however, there is lack of robust quantitative biogeographical or physiological evidence to support or refute the existence of such ecotypes. Between coccolithophore species, coccolith morphology dictates calcium carbonate content so that different species or morphotypes have varying levels of calcium carbonate (Fig. 1) and differ in their potential to influence the marine carbon cycle.

Coccolithophores have a long geological history, evolving around 220 million years ago, providing a rich proxy record that has been used to reconstruct past environmental changes. Organic biomarkers originating from haptophytes (e.g. alkenones), the taxonomic group that coccolithophores are affiliated with, are used to reconstruct ocean temperatures in the past. However, differences in organic biochemistry between closely related species (such as the E. huxleyi morphotypes), which may have strongly different biogeographical distributions, has not been examined in detail. Such differences may impact past climate reconstructions and so there is a need to examine organic biomarkers in the context of species level responses to environmental temperature and resource availability (light, nutrients) to ensure accurate paleo-proxy interpretation.

This studentship is designed to provide the student with a broad multidisciplinary skill set, from image analysis to biogeographical modelling and organic geochemistry, as well as allowing a global perspective on the impact of biodiversity on calcite production and the marine carbon cycle. This studentship will collect the necessary quantitative data to test for the existence and impact of different E. huxleyi ecotypes on the marine carbon cycle and organic biomarker interpretation. The studentship will take a multidisciplinary approach, including biogeographical, physiological, bio-molecular and modelling studies.

The student will take advantage of material collected and models developed through independently funded NERC projects working in the Iceland Basin (in 2024) to examine Coccolithophore controls on ocean alkalinity (NE/Y004736/1) and developing Machine Learning tools to reveal coccolithophore trait diversity and its climatic impacts (NE/X001261/1, 2022-2026). Collaborating with the teams of researchers involved in these projects will provide significant networking and career development opportunities.


The experience and diverse expertise of the supervisory team (Poulton, McClymont, Monteiro) will allow for the student to receive full training in the analytical and statistical techniques required for the studentship; prior experience in these techniques is not essential. Utilizing an existing global archive of Scanning Electron Microscopy (SEM) images, the student will define and test the biometric characteristics of the different E. huxleyi morphotypes proposed in the literature and in existence in culture collections. With a well-defined biometric matrix of morphotype identity, the student will utilize the SEM image archive to examine the pole to pole distribution of the different morphotypes, using multivariate statistics to examine spatial patterns in the context of environmental controls (temperature, resource availability). The student will use laboratory cultures of the different morphotypes to test their physiological (e.g., growth rate, photo-physiology, bio-molecular composition) responses to temperature variability. The laboratory cultures will include determination of organic biomarker composition across temperature and resource gradients, with utilization of analytical facilities in Durham. The biogeographical and physiological information gained will be combined within a Species Distribution Model (in collaboration with Dr Fanny Monteiro, Bristol) to globally map the distribution of the different E. huxleyi morphotypes, and examine how this impacts estimates of global calcium carbonate production under different warming scenarios.

A number of opportunities for fieldwork will be explored to collect further information on morphotype distribution along strong temperature and resource availability gradients; for example, from the equatorial Atlantic to Benguela upwelling and South Atlantic Ocean in 2025.

The studentship will have strong ties to a number of funded NERC and EU projects examining coccolithophore dynamics, biodiversity and their controls on ocean alkalinity; this will allow the student to network across diverse communities of international researchers and experience multidisciplinary teams, as well as putting their research into a wider context of policy development around the marine carbon cycle.


Eligibility is under UKRI Terms and Conditions, which means that UK and International candidates may apply. For International Students, UKRI only pay the equivalent of home fees. The differential between home and international fees will likely need to be self-funded. International applicants need to contact the primary supervisor (Prof Alex Poulton, [Email Address Removed]) of the project by no later than Monday 11th December 2023 in order to be considered for shortlisting.

How to Apply

All prospective students need to complete the online IAPETUS2 form (link here). Before completing this form, please read the DTP privacy policy as you will need to tick that you have read and understood this.

Both parts of the application must be made by Friday 5th January 2023 at 12pm (GMT), which is the public deadline for applications that will apply across all of the Partnership. 

Environmental Sciences (13) Geology (18)

Funding Notes

APETUS2’s postgraduate scholarships are tenable for up to 3.5 years and provide the following package of financial support:
A tax-free maintenance grant set at the UK Research Council’s national rate, which in 2023/24 is £18,622;
Payment of tuition fees at the Home rate*;
Access to extensive research support funding; &
Support for an external placement of up to six months.
Part-time award-holders are funded for seven years and receive a maintenance grant at 50% of the full-time rate.
*Eligibility is under UKRI terms and conditions. International Students can apply but it is expected that the differential between home and international fees will likely be self-funded.


Poulton, A.J. (2019). Phytoplankton, Calcareous Nanoplankton – The Coccolithophores. In J.K. Cochran, H.J. Bokuniewicz, & P.L. Yaker (Eds.), Encyclopedia of Ocean Sciences (3rd Edition, Vol. 1, pp. 606-612).
De Vries, J.C., Monteiro, F.M., Wheeler, G., Poulton, A., Godrijan, J., Cerino, F., Malinverno, E., Langer, G., Brownlee, C. (2021). Haplo-diplontic life cycle expands coccolithophore niche. Biogeosciences, 18, 1161-1184.
Charalampopoulou, A., Poulton, A.J., Bakker, D.C.E., Lucas, M.I., Stinchcombe, M.C., Tyrrell, T. (2016). Environmental drivers of coccolithophore abundance and calcification across Drake Passage (Southern Ocean). Biogeosciences 13, 5917-5935.
McClymont, E.L., Elmore, A.C., Kender, S., Leng, M.J., Greaves, M., Elderfield, H. (2016). Pliocene-Pleistocene evolution of sea surface and intermediate water temperatures from the southwest Pacific. Paleoceanography and Paleoclimatology, 31, 895-913.
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