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08 May 2008
Increased carbon dioxide in the atmosphere is causing microscopic ocean plants to produce more calcium carbonate, or chalk, – with potentially wide-ranging implications for climate modelling.
An international team of scientists including Dr Ian Hall of the School of Earth and Ocean Sciences have just made the surprising discovery about a species of phytoplankton. This group of single-celled marine plants (coccolithopores) is extremely widespread and their deposits have formed chalk and limestone rocks such as the White Cliffs of Dover.
Previously, the fact that increasing carbon dioxide made the oceans more acidic was thought to be harmful to all organisms that produce calcium carbonate (calcification), including the coccolithophores. However, as reported in the journal Science, observations in the laboratory and the deep ocean have shown that the calcification of coccolithophores increases significantly with the rising carbon dioxide levels produced by human activity.
The research also showed that over the past 220 years, coccolithophores have increased the mass of calcium carbonate they each produce by around 40 per cent. However the study also showed that that the rise in carbon dioxide from increased calcification is offset by its removal through increased photosynthesis by the phyloplankton.
Dr Hall said: "This work is potentially of great importance as it contradicts previous findings and shows that calcification by phytoplankton could double by the end of this century. This is significant since the amount of calcium carbonate produced in the upper ocean has a direct influence of atmospheric carbon dioxide. We now plan to conduct work on additional marine sediment cores from different oceans, particularly those most susceptible to ocean acidification, such as the Southern Ocean, and determine exactly what the effect of increased calcification will be."
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