Earth Sciences

Microscopic ocean plankton called coccolithophores are providing clues about the impact of climate change both now and many millions of years ago.

The study by scientists from UCL (Paul Bown, Cherry Newsam and Jeremy Young) and the National Oceanography Centre, Southampton, found that their response to environmental change varies between species, in terms of how quickly they grow.

Coccolithophores, a type of planktonic algae, are not only widespread in the modern ocean but they are also prolific in the fossil record because their tiny calcium carbonate shells are preserved on the seafloor after death – the vast chalk cliffs of southern England, for example, are almost entirely made of fossilised coccolithophores.

The fate of coccolithophores under changing environmental conditions is of interest because of their important role in the marine ecosystem and global carbon cycle. Because of their calcite shells, these organisms are potentially sensitive to ocean acidification, which occurs when rising atmospheric carbon dioxide (CO2) is absorbed by the ocean, increasing its acidity.

There are many different species of coccolithophore and in the article, published in Nature Geoscience this week, the scientists report that they responded in different ways to a rapid climate-warming event that occurred 56 million years ago, the Palaeocene-Eocene Thermal Maximum (PETM). By comparing immaculately preserved and complete fossil cells with modern coccolithophore cells, the researchers could interpret how different species responded to the sudden increase in environmental change at the PETM, when atmospheric CO2 levels increased rapidly and the oceans became more acidic. The species Toweius pertusus continued to reproduce quickly despite rapidly changing environmental conditions. This would have provided a competitive advantage and is perhaps why closely-related modern-day species considered to be its descendants, such as Emiliana huxleyi, still thrive today.

In contrast, the species Coccolithus pelagicus grew more slowly during the period of greatest warmth and this inability to maintain high growth rates may explain why its descendants are less abundant and less widespread in the modern ocean.

This collaborative study, which links modern and palaeo research, was primarily supported by the UK Ocean Acidification (UKOA) Research Programme, which is jointly funded by the Natural Environment Research Council (NERC), the Department of Environment, Food and Rural Affairs (Defra) and the Department of Energy and Climate Change (DECC). It was also supported by Royal Society and NERC Fellowships. UKOA aims to reduce uncertainties in the response of marine organisms, ecosystems and biogeochemistry to ocean acidification and other climate related stressors. 

Further reading: Palaeontology: Plankton in a greenhouse world by Gerald Langer.
Nature Geoscience 6, 164–165 (2013) doi:10.1038/ngeo1750

Reference: Gibbs S.J., Poulton A.J., Bown P.R., Daniels C.J., Hopkins J. Young J.R., Jones H.L., Thiemann G.J., O’Dea S.A., Newsam C. (2013) Species-specific growth response of coccolithophores to Palaeocene–Eocene environmental change. Nature Geoscience doi: 10.1038/NGEO1719