How do calcifying marine organisms grow? Determining the role of non-classical precipitation processes in biogenic marine calcite formation

Dr Christopher Pearce, Dr David Evans, UoS; Professor Sumeet Mahajan, UoS

The shells of planktonic marine calcifying organisms represent one of the largest long-term carbon sinks on Earth’s surface and are an important archive of geochemical systems that record past climate change. As such, and because the response of these organisms to anthropogenic climate change may be an important carbon cycle feedback, it is vitally important to understand how these organisms calcify. There is growing evidence that most marine calcifying organisms produce crystalline calcite or aragonite (CaCO3) via a ‘precursor’ phase, usually amorphous calcium carbonate (ACC) [1]. However, no laboratory experiment has succeeded in producing CaCO3 via an amorphous precursor with the characteristics of biological marine calcites. Solving this issue would constrain an important component of the biomineralisation process and enable us to understand the sensitivity of calcification to past, present, and future environmental change.

This project will experimentally determine the physical and chemical conditions required to form calcite via ACC with the geochemical and structural properties of that of marine organisms. Ultimately, the project will build this information into a biomineralisation model to help mechanistically underpin our understanding of the extent to which marine organisms will be impacted by future climate change and ocean acidification.



As the most abundant CaCO3 producers in the modern ocean, the project will primarily focus on understanding the biomineralisation processes of the ‘low-magnesium’ planktonic foraminifera. Previous work has shown that inorganic ACC precipitated from seawater contains ~10-100 times more MgCO3 than foraminiferal calcite [2], such that a key goal will be to understand how low-Mg calcite can be formed via a nonclassical pathway. To do so, the project will:

1] Produce crystalline CaCO3 with the properties of foraminiferal calcite by conducting titration experiments under a wide range of environmental and chemical conditions to determine how these impact the polymorph and geochemistry of the resulting crystalline phase.

2] Mechanistically understand how ACC transforms into crystalline CaCO3 by using isotopic tracers coupled with Raman spectroscopy.

3] Increase the complexity of the system by conducting experiments in the presence of organic molecules extracted from the intra-crystalline organic component of modern marine organisms, which have been implicated in stabilising ACC and directing crystallisation [3].

Ultimately, the project aims to artificially produce calcite via ACC with the chemical characteristics of that of the foraminifera for the first time, and to apply this knowledge to determining the sensitivity of these organisms to future climate change.



The INSPIRE DTP 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. The student will be registered at the University of Southampton and hosted at the School of Ocean and Earth Science.

The project will provide interdisciplinary training and transferable skills that will add value for a career in academia or industry. Specifically, the candidate will be trained in:

  • The use of computer-controlled titration equipment and the production of amorphous and crystalline materials under highly controlled conditions.
  • Analytical geochemistry, including working in ultra-clean laboratories, the operation of (multi collector) inductively coupled plasma mass spectrometers, and data processing.
  • The use of Raman spectroscopy to track precipitation and crystallisation in situ.
  • The development and application of numerical models to geochemical datasets and (bio)mineralisation.
  • Proficiency in programming languages (Matlab/python) including for the purposes of building geochemical models.
  • Quantitative and qualitative analytical skills.
  • Scientific communication through multiple media and at various local, national and international conferences/meetings.
  • The project may contain the possibility to gain experience in working with live marine organisms, depending on the project trajectory and individual preference.


Eligibility & Funding Details: 

Please see for details.


Background Reading: 

[1] Sviben, S., et al. (2016) A vacuole-like compartment concentrates a disordered calcium phase in a key coccolithophorid alga. Nature Communications 7, 11228.

[2] Evans, D., et al. (2020) Trace and major element incorporation into amorphous calcium carbonate (ACC) precipitated from seawater. Geochimica et Cosmochimica Acta 290, 293.

[3] Tyszka, J., et al. (2019) Form and function of F-actin during biomineralization revealed from live experiments on foraminifera. PNAS, 116, 4111.