Clue to carbon storage in the Southern Ocean

Carbon is channelled deep into the sea through a funnel-like mechanism. tbdevries

Carbon emissions are drawn deep into the Southern Ocean by plunging currents, scientists have found, challenging the idea that carbon is locked away from the atmosphere by being absorbed across vast areas of ocean.

The team of scientists from the British Antarctic Survey and CSIRO found carbon makes its way into the sea through funnels created by a combination of winds, currents and massive whirlpools which carry warm and cold water around the ocean.

This carbon capture process occurs in well-defined regions in the Southern Ocean, which the researchers have mapped.

The findings are published today in Nature Geoscience.

“The Southern Ocean is a large window by which the atmosphere connects to the interior of the ocean below,” said lead author Dr Jean-Baptiste Sallée from the British Antarctic Survey.

“Until now we didn’t know exactly the physical processes of how carbon ends up being stored deep in the ocean,” he said.

The team explored the workings of the ocean with the help of small robotic probes, known as Argo floats, which dive to depths of two kilometres. The researchers also analysed temperature, salinity and pressure data.

Study co-author Dr Richard Matear from CSIRO’s Marine and Atmospheric Research division said the investigators focused on how carbon was transferred from the surface layer into the ocean interior because “the process sets how much carbon the ocean can take up,” he said.

“The ocean plays a really important role in the uptake of our anthropogenic carbon emissions. About a quarter of our CO2 emissions end up in the ocean and the Southern Ocean accounts for almost half (40%) of that number.”

The map of carbon capture in the Southern Ocean will be used to model climate change projections and help assess potential methods to increase the ocean’s carbon capture.

Carlos Duarte, Director of the University of Western Australia’s Oceans Institute, said the Southern Ocean was known as a carbon sink, but until now “the suite of processes responsible for this sink was poorly understood”.

Professor Duarte said the findings would give researchers a better grasp of the role the Southern Ocean played in the uptake of CO2 by the ocean. “The new estimate will not alter the global estimate, which is independently constrained, but gives a quantitative understanding of the processes involved,” he said.

“Researchers will now be able to explore possible changes in this role as ocean dynamics change – not just from climate change, but from other impacts such as changes in atmospheric circulation over the Southern Ocean, driven by the depletion of the ozone layer over Antarctica.”