Study expedition crossing Drake Passage in the Southern Ocean (Photo: British Antarctic Survey (BAS))

Study expedition crossing Drake Passage in the Southern Ocean (Photo: British Antarctic Survey (BAS))

Scientists have discovered  how carbon dioxide is drawn from the atmosphere and stored  deep in the ocean.

According to a new study published in Nature Geoscience, instead of CO2 being evenly absorbed deep into the water over wide areas of the Southern Ocean, it is pulled down and locked away from the atmosphere through localized pathways  created by a combination of winds, currents and  whirlpools that are 1,000 kilometers wide.

The world’s oceans help ease climate change by absorbing carbon dioxide in a process called carbon sequestration.  The Southern Ocean is considered to be one the most important carbon sinks in the world, absorbing around 40 percent of the annual global CO2 emissions.

“The Southern Ocean is a large window by which the atmosphere connects to the interior of the ocean below. Until now we didn’t know exactly the physical processes of how carbon ends up being stored deep in the ocean,” says the paper’s lead author, Dr. Jean-Baptiste Sallée from British Antarctic Survey. “It’s the combination of winds, currents and eddies that create these carbon-capturing pathways drawing waters down into the deep ocean from the ocean surface.”

Because of the Southern Ocean’s size and remoteness, researchers have only just begun to explore the mechanisms of the ocean with the help of small robotic probes called Argo floats.

The robotic probes are just over a meter in length and can dive  about two kilometers.  Eighty of these floats were set out in the Southern Ocean back in 2002  to collect information on the ocean’s temperature and salinity. Ten years of observations from these probes allowed  scientists to study this remote area of the world for the  first time.

Australian oceanographer and Southern Ocean specialist Steve Rintoul explains how the ocean absorbs CO2.
(Video: Commonwealth Scientific and Industrial Research Organisation)

The researchers were also able to gather further information, such as water temperature, salinity and pressure, by using an instrument called the CTD profiler, a cluster of sensors which records measurements as it is lowered deep into the ocean to depths of more than seven kilometers.

“Now that we have an improved understanding of the mechanisms for carbon draw-down we are better placed to understand the effects of changing climate and future carbon absorption by the ocean,” says  Sallée.”