Plankton enables enhanced carbon consumption in the ocean, finds study

A study published in the framework of the EU-funded CARBOOCEAN project in Nature reveals that ocean plankton will increase its consumption of dissolved inorganic carbon by up to 39% when CO2 concentration rises.

While plankton will thereby contribute to a dampening of the greenhouse effect on a global scale, higher consumption will speed up the acidification of the deep ocean and decrease its oxygen concentrations. It will also degrade the nutritional quality of plankton, although the initial increase in CO2 intake will act as a fertiliser on plankton, scientists say.

Other studies have shown the effects of acidification on calcifying organisms such as corals, molluscs and the like, but little is known about consequences at community or ecosystem level. Generally, current models of the development of global climate barely take into account the reaction of marine organisms and the processes that they influence, according to scientists in the research group, headed by the Leibniz Institute of Marine Sciences (IFM-GEOMAR) in Kiel, Germany.

‘We need to learn a lot more about the biology of the oceans, because the organisms play a decisive role in the carbon cycle,’ says Professor Ulf Riebesell, marine biologists at IFM-GEOMAR and first author of the study. ‘How do they affect the chemical balance and what are their responses to the enormous environmental changes we are currently experiencing?’

The experimental set-up in the Raunefjord close to the Norwegian city of Bergen simulated different stages of CO2 concentration from current levels to that predicted for the year 2100 and for 2150 in enclosed systems or mesocosms.

Observation showed that the tiny plankton organisms ‘act as a biological conveyor belt for the transport of carbon dioxide out of the surface and into the deep ocean’, the researchers explain, as they take CO2 to deeper levels of the ocean when they die. However, decomposition of the increased mass of plankton will require more oxygen, which will in turn have a negative effect on marine animals in deep habitats. Furthermore, planktonic crustaceans that were fed CO2-enriched microalgae displayed slower growth rates and were less proliferous.

‘Our results probably represent only the tip of the iceberg,’ Professor Riebesell concludes. ‘I am certain that scientists will discover further biological feedback mechanisms in the near future. It is essential not only to identify and to understand these mechanisms, but also to quantify their effect on the global climate system, now and in the future.’

Within the CARBOOCEAN project, 35 partners from 15 countries inside and outside the EU are attempting to assess marine carbon sources and sinks with a special emphasis on the Atlantic and Southern oceans, as the world’s oceans are by far the largest sink of man-made CO2 (nearly half of CO2 emitted through burning of fossil fuels since pre-industrial times). CARBOOCEAN receives €14.5 million of its total cost of over €19 million in funding under the Sixth Framework Programme’s (FP6) sustainable development theme.
Cordis News, 13 November 2007. Press release.

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