Microscopic ocean algae called coccolithophores are providing clues about the impact of climate change both now and many millions of years ago. The study found that their response to environmental change varies between species, in terms of how quickly they grow.
Coccolithophores, a type of plankton, 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 Dover, 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 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 an 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).
The study, involving researchers from the University of Southampton, the National Oceanography Centre and University College London, found that the species Toweius pertusus continued to reproduce relatively 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 work provides us with a whole new way of looking at living and fossil coccolithophores," said lead author Dr Samantha Gibbs, Senior Research Fellow at University of Southampton Ocean and Earth Science.
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.
"We use knowledge of how coccolithophores build their calcite skeletons in the modern ocean to interpret how climate change 56 million years ago affected the growth of these microscopic plankton," said co-author Dr Alex Poulton, a Research Fellow at the National Oceanography Centre.
"This is a significant step forward and allows us to view fossils as cells rather than dead 'rocks'. Through this we can begin to understand the environmental controls on oceanic calcification, as well as the potential effects of climate change and ocean acidification."
The study was primarily supported by the UK Ocean Acidification 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).
Notes to editors
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
The image shows fossil and modern coccolithophore cells of species Toweius pertusus and Coccolithus pelagicus. Courtesy of Paul Bown, University College London (UCL).
This collaborative study, which straddles modern and palaeo research, arose from linkages within the UK Ocean Acidification research programme (UKOA, co-funded by NERC, Defra and 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 information on UKOA can be found at: www.oceanacidification.org.uk
The study was led by the University of Southampton Ocean and Earth Science, based at the National Oceanography Centre, Southampton (NOCS). Co-authors were from NOCS itself and University College London (UCL).
The National Oceanography Centre (NOC) is the UK's leading institution for integrated coastal and deep ocean research. NOC operates the Royal Research Ships James Cook and Discovery on behalf of the Natural Environment Research Council, and develops technology for coastal and deep ocean research. Working with its partners NOC provides long-term marine science capability including: sustained ocean observing, mapping and surveying, data management and scientific advice.
NOC operates at two sites, Southampton and Liverpool, with the headquarters based in Southampton.
Among the resources that NOC provides on behalf of the UK are the British Oceanographic Data Centre (BODC), the Marine Autonomous and Robotic Systems (MARS) facility, the National Tide and Sea Level Facility (NTSLF), the Permanent Service for Mean Sea Level (PSMSL) and British Ocean Sediment Core Research Facility (BOSCORF).
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