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Ozone hole shrinks atmospheric CO2 uptake in Southern Ocean

Researchers in Europe have discovered that the ozone affects the ocean's role as a carbon sink, a reservoir that absorbs and stores carbon from another part of the carbon cycle. The four sinks are the atmosphere, terrestrial biosphere, oceans and sediments. The findings, publi...

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Researchers in Europe have discovered that the ozone affects the ocean's role as a carbon sink, a reservoir that absorbs and stores carbon from another part of the carbon cycle. The four sinks are the atmosphere, terrestrial biosphere, oceans and sediments. The findings, published in the journal Geophysical Research Letters, will help improve future models developed by the Intergovernmental Panel on Climate Change (IPCC) that assesses the scientific, technical and socioeconomic information needed for the understanding of the risk of human-induced climate change.

The results are part of the CARBOOCEAN ('Marine carbon sources and sinks assessment') project, backed with EUR 14.5 million in funding under the 'Sustainable development' Thematic area of the EU's Sixth Framework Programme (FP6). CARBOOCEAN targeted 'the reduction of existing uncertainties in the quantification of net annual air-sea CO2 fluxes by a factor of two for the world ocean and by a factor of four for the Atlantic Ocean'.

In this latest study, researchers from three laboratories in France used original simulations to show that the ozone layer hole shrinks atmospheric carbon uptake in the Southern Ocean and helps raise ocean acidity.

Human activities directly impact the levels of carbon dioxide (CO2) in the atmosphere; in turn, these higher levels contribute to global warming. The Southern Ocean, which absorbs nearly 15% of anthropogenic carbon released each year, is one of the main sinks for atmospheric CO2. The problem, however, is that its effectiveness is declining. The researchers found that the saturation of the carbon sink in the Southern Ocean has not been correctly simulated by the climate models used.

Oceanographers, climatologists and modellers teamed up to develop a model that more accurately simulates the Southern Ocean's ability to act as a carbon sink. The team based their assessments on the coupled ocean/atmosphere model of the Institut Pierre Simon Laplace (IPSL) in France. The model has been integrating the carbon cycle and taking into account changes in the concentration of stratospheric ozone for the past 34 years, according to the researchers.

'The simulations obtained with this model accurately reproduce the oceanic observations obtained in the field over the last few years,' explained Dr Nicolas Metzl, a researcher at Laboratoire d'Océanographie et du Climat: Expérimentation et Approches Numériques (LOCEAN/IPSL).'

Overall, the study drew attention to two major phenomena concerning the Southern Ocean: CO2 uptake shrank considerably and the acidification of high southern latitude oceanic water grew more rapidly. Some 2.3 billion tonnes of carbon were not taken up by oceans from 1987 to 2004, the team said. This corresponds to a relative decrease of almost a tenth of the global ocean carbon uptake, they added.

Also, the study showed how existing climate models have overestimated oceanic carbon uptake and underestimated ocean acidification. The ozone must be considered in future modelling, said the researchers, adding that this would enhance future climate predictions.

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France