CANBERRA, Australia, July 31, 2012 (ENS) – A team of British and Australian scientists has discovered how the greenhouse gas carbon dioxide, CO2, is drawn down from the surface of the Southern Ocean to the deep waters beneath.
The Southern Ocean is an important carbon sink in the world. Around 40 percent of the annual global CO2 emissions absorbed by the world’s oceans enter through this region.
Carbon dioxide is not absorbed uniformly into the deep ocean in vast areas. Instead, it is drawn down and locked away from the atmosphere by plunging currents a thousand kilometers wide, according to the study published this week in the journal “Nature Geoscience.”
The team includes scientists from the British Antarctic Survey and Australia’s national research agency, the Commonwealth Scientific and Industrial Research Organisation, CSIRO.
“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,” said Dr. Jean-Baptiste Sallée of the British Antarctic Survey.
Winds, currents and massive whirlpools called eddies that carry warm and cold water around the ocean create localized pathways or funnels for carbon to be stored, the scientists have learned.
Lead author, Dr. Sallée said, “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. 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.”
CSIRO co-author, Dr. Richard Matear says limiting step in the uptake by the ocean of the carbon dioxide emitted by human activities is the physical transport of the gas from the surface into the ocean interior.
“Our study identifies these pathways for the first time and this matches well with observationally-derived estimates of carbon storage in the ocean interior,” Dr. Matear said.
Due to the size and remote location of the Southern Ocean, scientists have only recently been able to explore the workings of the ocean with the help of small robotic probes – known as Argo floats.
In 2002, 80 floats were deployed in the Southern Ocean to collect information on the temperature and salinity. This unique set of observations spanning 10 years has enabled scientists to investigate this remote region of the world for the first time.
The floats are just over one meter (39 inches) in length and dive to depths of two kilometers (1.2 miles).
Today, there are over 3,000 floats in the oceans worldwide providing detailed information used in oceanic climate models.
The British-Australian team also analyzed temperature, salinity and pressure data collected from ship-based observations since the 1990s. The data was gathered with clusters of sensors taking measurements as they were lowered into the ocean to depths of more than seven kilometers (4.3 miles).
The work was supported through the Wealth from Oceans and Australian Climate Change Science Programs, and the Australian Government’s Cooperative Research Centre program.