Context

Observations from research aircraft show that the Southern Ocean absorbs much more carbon from the atmosphere than it releases, confirming it is a very strong carbon sink and an important buffer for the effects of human-caused greenhouse gas emissions, according to a new, NASA-supported study.

Background

• In recent years various studies were conducted which suggested the Southern Ocean might be less of a sink than previously thought.
• The present study is 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.

Analysis

What has been found?

• The findings provide clarity about the role the icy waters surrounding Antarctica play in buffering the impact of increasing greenhouse gas emissions.
• The research also highlights the power that airborne observations have to reveal critical patterns in the global carbon cycle.
• Airborne measurements show a drawdown of CO2 in the lower atmosphere over the Southern Ocean surface in summer, indicating carbon uptake by the ocean.
• The findings highlight the importance of aircraft-based observations to understand carbon cycling.

About Southern Ocean The Southern Ocean is a body of salt water covering the portions of the world ocean and tributary seas surrounding Antarctica below 60° S. It is also known as the Austral Ocean or the Antarctic Ocean. The Southern Ocean is indeed a significant carbon sink -- absorbing a large amount of the excess carbon dioxide emitted into the atmosphere by human activities.

What is the basis of measurement?

• Those studies relied on measurements of ocean acidity – which increases when ocean water absorbs CO2 – taken by instruments that float in the ocean.
• When CO2 is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions.
• This increase causes the seawater to become more acidic and causes carbonate ions to be relatively less abundant.

Carbonate ions Carbonate ions are an important building block of structures such as sea shells and coral skeletons. Decreases in carbonate ions can make building and maintaining shells and other calcium carbonate structures difficult for calcifying organisms such as oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton.

• Ocean acidification is affecting the entire world’s oceans, including coastal estuaries and waterways.

How Oceans act as a carbon sponge?

• When human emissions of CO2 enter the atmosphere, some of that gas is absorbed by the ocean, slowing the rise in global temperature and climate change.
• Cold water from the deep ocean rises to the surface through a process called upwelling.
• Once at the surface, that colder water absorbs CO2 in the atmosphere – often with the help of photosynthesizing organisms called phytoplankton – before sinking again.

Conclusion

As society continues to emit more CO2, understanding the location, scale and variability of carbon sinks is crucial to understand the future trajectory of climate change, and evaluating the impact of future emission reductions measures and CO2 removal technologies.