Environmental controls on calcification of phytoplankton from the geological record

Key Questions

Which environmental parameters control calcification efficiency in coccolithophores and foraminifera in time and space?

Background

Why are the oceans supersaturated with respect to calcium carbonate? Foraminifera and coccolithophores generate over 2 billion tonnes of carbonate/yr1 but what limits this production? Our lack of understanding of the response of pelagic calcification to environmental change hinders any predictions of the future ocean carbon cycle and ecosystem. The main objective of this project is to bring together a physiological model of C with innovative stable isotopic approaches applied to the natural laboratory of the geological record to identify the environmental parameters that trigger the highest pelagic adapted calcification efficiency in the modern and Cenozoic ocean.

Aims of the Project

Use novel stable isotopic approaches, and sedimentological methods to reconstruct the calcification efficiency of pelagic calcifiers in the modern and past ocean and assess their sensitivity to environmental parameters.

Project Description

The main objective of this project is to bring together a physiological model of C with innovative stable isotopic approaches applied to the natural laboratory of the geological record to identify the environmental parameters that trigger the highest pelagic adapted calcification efficiency in the modern and Cenozoic ocean. A second objective will be to generate MAR of different coccolith and foraminiferal size fractions to understand how the environmental may influence their changing contribution to the carbonate sink of the ocean. Ultimately, the project will investigate how the environmental sensitivity of calcite production rates, and their carbon isotopic composition, impacts understanding of the past and prediction of the future carbon cycle through use of the cGENIE intermediate complexity model.

The project will use a novel methodology to reconstruct the calcification rate of individual species and the community, composition independent of preservation, over the geological past and across the modern ocean. Size-separated coccolithophore and foraminifera vital effects, the isotopic departure of biominerals from equilibrium are variable in response to the environment and physiology but can be mechanistically understood with a physiological model. This model shows that vital effect expression is driven by the ratio of carbon supply to carbon demand and the PIC/POC ratio. Calcification efficiency over the Cenozoic can then be inferred from the PIC/POC ratio of each species in each size fraction and supported by detailed morphometry, SEM and light microscopy.

LM Claxton, HLO McClelland, M Hermoso, REM Rickaby, Eocene emergence of highly calcifying coccolithophores despite declining atmospheric CO2, Nature Geoscience, 1-6

Hermoso, M, McClelland, H.-L.O., Hirst, J.S., Minoletti, F., Bonifacie, M., Rickaby, R.E.M. Towards the use of the coccolith vital effects in palaeoceanography: A field investigation during the middle Miocene in the SW Pacific Ocean, Deep-Sea Research Part I, 160, Art. No. 103262, 2020

Si, W. and Rosenthal, Y., (2019). Reduced continental weathering and marine calcification linked to late Neogene decline in atmospheric CO2. Nature Geoscience. https://doi.org/10.1038/s41561-019-0450-3

McClelland H. L. O., J. Bruggeman, M. Hermoso & R. E. M. Rickaby, The origin of carbon isotope vital effects in coccolith calcite, Nat Comms, DOI: 10.1038/ncomms14511, 2017

Lee, R. B. Y., Mavridou, D., Papdakos,G., McLelland, H. L. O., and R. E. M. Rickaby, The Uronic acid content of coccolith associated polysaccharide provides insights into evolving coccolithogenesis and climate, Nat. Comms, doi:10.1038/ncomms13144, 2016.

Rickaby, R. E. M., J. Henderiks, and J. N. Young, Perturbing phytoplankton: response and isotopic fractionation with changing carbonate chemistry in two coccolithophore species, Clim. Past, 6, 771-785, 2010.

Methods to be used

Micropalaeontology, stable isotope analyses, carbonate cycle, cellular and earth system models.

Specialised skills required

Some knowledge of microfossils very helpful but also knowledge of modelling languages and how to approach quantitative modelling.

Please contact Ros Rickaby on rosr@earth.ox.ac.uk if you are interested in this project.  The project will be co-supervised by Craig Dedman craig.dedman@earth.ox.ac.uk and Alba Gonzalez-Lanchas alba.gonzalez-lanchas@earth.ox.ac.uk, Department of Earth Sciences.