Marine life may temper global warming

Gephyrocapsa oceanica was studied under lab conditions

Scientists in Germany believe that an important group of marine plankton could play a crucial role in determining the speed at which any global warming might proceed.

The tiny but abundant marine organisms called coccolithophorids - free-floating equivalents of corals - produce their own carbon dioxide as a by-product of making their skeletons.

But if atmospheric CO2 rises in accordance with some models, the world's oceans are likely to become more acidic - a development that will interfere with the skeleton making process.

This, the researchers say, will allow the oceans to become a bigger sink for human carbon emissions, producing a "negative feedback" that should counteract global warming.

"As calcification actually releases carbon dioxide into the seawater, a slow-down in calcite production therefore increases the ocean's capacity to store the greenhouse gas," lead researcher Ulf Riebesell, from the Alfred Wegener Institute in Bremerhaven, told the BBC.

Norwegian fjord

But he warned that the changing behaviour of the coccolithophorids would only temper the expected rises in atmospheric CO2.

"The additional carbon dioxide potentially stored in the oceans because of decreasing calcification amounts to, at most, 30 billion tonnes of carbon over the next 100 years," Dr Riebesell said.

"Fossil fuel burning, on the other hand, releases some six billion tonnes of carbon into the atmosphere every year. So it would take us just a few years to fill up the CO2 sink gradually developing over the next 100 years."

Dr Riebesell and his colleagues studied two species of coccolithophorids (Emiliania huxleyi and Gephyrocapsa oceanica) under laboratory conditions. By adding acid or base to the growth medium in which the organisms were kept, the scientists were able to simulate different ocean scenarios.

"We knew that increased atmospheric CO2 would impair conditions for calcite production in the ocean, but we had expected that the organisms would be able to compensate for this - apparently they cannot."

The team now plan to extend some of the their field work by looking at how the organisms living in a Norwegian fjord respond to raised levels of CO2.