The Southern Ocean is an important carbon sink, absorbing a large amount of the excess carbon dioxide emitted into the atmosphere by human activities, according to a new study led by the National Center for Atmospheric Research (NCAR).
The new study makes use of observations from research aircraft flown during three field projects over nearly a decade, as well as a collection of atmospheric models, to determine that the Southern Ocean takes up significantly more carbon than it releases.
“Airborne measurements show a drawdown of CO2 in the lower atmosphere over the Southern Ocean surface in summer, indicating carbon uptake by the ocean”, said Matthew Long, the paper’s lead author.
For a long time, scientists have thought that the Southern Ocean is an important carbon sink. In the region around Antarctica, cold water from the deep ocean travels to the surface. This rising water may not have seen the surface of the ocean for hundreds of years – but once in contact with the atmosphere, it’s able to absorb CO2 before sinking again.
Measurements of CO2 and related properties in the ocean indicate that 40 percent of all human-produced CO2 now stored in the ocean was originally taken up by the Southern Ocean. But measuring the balance at the surface – the back and forth exchange of CO2 between the water and the overlying air throughout the year – has been challenging.
In the new study, the researchers sought to address the uncertainty by looking at carbon in the air instead of in the water. The atmosphere and the ocean are in balance, and they are constantly exchanging CO2, oxygen, and other gases with each other.
The research team turned to a suite of atmospheric models to help them translate their atmospheric profiles into an estimate of how much CO2 the ocean was soaking up or releasing. They concluded that the Southern Ocean takes in significantly more carbon in the summer than it loses during the winter, absorbing a whopping 2 billion tons of CO2 over the course of a year. In the summer, blooms of photosynthetic algae, or phytoplankton, play a key role in driving CO2 uptake into the ocean.
https://phys.org/news/2021-12-aircraft-reveal-surprisingly-strong-southern.html