30 July 2012

Huge carbon-sucking funnels found in Southern Ocean

Agençe France-Presse
Wind, eddies and currents work together to create 1,000 km-wide, carbon dioxide-sucking funnels that takes Earth-warming carbon deep into the Southern Ocean to be safely locked away. But the process may itself be threatened by climate change.
Climate change water vortex_COSMOS science magazine

Carbon dioxide is sucked into the Southern Ocean through huge funnels. This process stores carbon, but may itself be threatened by climate change. Credit: iStockphoto

PARIS: Wind, eddies and currents work together to create 1,000 km-wide, carbon-sucking funnels that takes Earth-warming carbon deep into the Southern Ocean to be safely locked away.

The process itself could be threatened by climate change, according to the research team from Britain and Australia that made the discovery, published in Nature Geoscience.

About a quarter of the carbon dioxide on Earth is stored away in its oceans – some 40% of that in the Southern Ocean encircling Antarctica, and this process adds to the toolkit of scientists attempting climate warming predictions.

Carbon locked away for thousands of years

At a depth of about 1,000 metres (3,200 feet), carbon can be locked away for hundreds to thousands of years, yet scientists had never been sure exactly how it gets there after dissolving into surface waters.

They had suspected the wind was the main force at play, pooling up surface water in some areas and forcing it down into the ocean depths.

Using 10 years of data obtained from small, deep-sea robotic probes, the researchers found that in addition to the wind, eddies – big whirlpool-like phenomena about 100km (60 miles) in diameter on average, also played a part.

Five 1,000 km-wide funnels

“You add the effect of these eddies and the effect of the wind and the effect of prominent currents in the Southern Ocean, you add these three effects, it makes … 1,000 km-wide funnels that bring the carbon from the sea surface to the interior,” said study author Jean-Baptiste Sallee.

The team had also used temperature, salinity and pressure data collected from ship-based observations since the 1990s.

“This is a very efficient process to bring carbon from the surface to the interior. We found in the Southern Ocean there are five such funnels,” said Sallee.

Climate change could affect the Southern Ocean

The team also found that the eddies counterbalanced a different effect of strong winds – that of releasing stored carbon by violent mixing of the sea.

“This does seem to be good news, but the thing is what will be the impact of climate change on the eddies? Will they stop, will they intensify? We have no idea,” said Sallee.

A changing climate could theoretically affect the nature and effect of the Southern Ocean eddies by changing ocean currents, intensifying winds or creating stark temperature spikes.

Climate models must include these eddies

The findings mean that eddies must be taken into account in future climate models, said Sallee. They are not currently.

The study focussed on the part of the Southern Ocean south of 35 degree south latitude.

The team could not say whether the same funnelling process would be at play in other seas, but Sallee said the Southern Ocean was “one of the most energetic places on Earth”, and the effect of eddies would likely be larger there than anywhere else.

There is also another carbon capturing process, not covered by this study, of CO2-producing micro organisms that live near the ocean surface sinking to the sea floor and settling there when they die.

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