Last reviewed September 2, 2026
The Southern Ocean performs an enormous climate service without making the underlying problem disappear. A 2024 modelling study reported by the British Antarctic Survey estimated that it accounted for 43 ± 3% of historical global ocean carbon uptake. That uptake slows the accumulation of carbon dioxide in the atmosphere. It also acidifies the water and moves carbon into a system whose future behaviour is not fixed.
How carbon enters the ocean
Carbon dioxide crosses the boundary between air and sea. Cold water can hold more dissolved gas than warm water, and strong Southern Ocean circulation continually brings water into contact with the atmosphere. Winds and currents then move some carbon away from the surface, where it may remain isolated from the atmosphere for decades or longer.
This physical pump is joined by a biological pump. Phytoplankton use carbon dioxide during photosynthesis. Some of the carbon in their cells and in the organisms that eat them sinks as organic material. Much is recycled near the surface; a smaller fraction reaches deeper water or sediment.
A sink is not a disposal site
Ocean uptake is sometimes described as though carbon simply vanishes. It does not. Dissolved carbon changes seawater chemistry, increasing acidity and reducing carbonate ions used by many organisms. NOAA estimates that the ocean has become about 26% more acidic on average over the past 250 years.
Nor is the sink guaranteed to grow in direct proportion to emissions. Wind, temperature, stratification, sea ice, circulation, and biological productivity all affect how much carbon crosses the surface and how long it stays away from the atmosphere.
Why the future capacity is uncertain
Warming has competing effects. It reduces the solubility of carbon dioxide, but changes in winds and circulation may expose different water masses to the atmosphere. Shifts in sea ice can alter both gas exchange and the seasonal biology of carbon uptake. The 2024 study projected that the Southern Ocean would remain responsible for close to half of global ocean carbon uptake in a middle-emissions scenario, even as its share of heat uptake became less dominant. Models still differ in the regional and temporal details.
The practical implication is plain. A natural sink is not an alternative to emissions reduction. If the ocean absorbs a smaller fraction of future emissions, more carbon remains in the atmosphere. If it absorbs a large fraction, the chemical and ecological consequences in the ocean increase.
What is known—and what is not
Known: the Southern Ocean is a major regional sink for human-emitted carbon; physical circulation and biological production both store carbon; uptake causes acidification.
Still uncertain: how circulation, stratification, sea ice, and ecosystem change will alter the sink’s strength and distribution over coming decades.