Southern Ocean Defies Climate Predictions, Maintaining Carbon Absorption Despite Global Warming

Southern Ocean’s Surprising Carbon Absorption Defies Climate Models

According to a new study published in Nature Climate Change, the Southern Ocean surrounding Antarctica continues to absorb significant amounts of carbon dioxide despite climate models predicting this capacity would weaken due to global warming. Researchers from the Alfred Wegener Institute report that long-term measurements show the ocean’s carbon absorption has remained largely unchanged in recent decades, contrary to what climate projections had indicated.

Southern Ocean’s Surprising Carbon Absorption Defies Climate Models
The Carbon Sink Paradox
Freshwater Creates Protective Barrier
Temporary Solution With Risks
Critical Need for Winter Data

The Carbon Sink Paradox

The report states that oceans collectively absorb approximately one quarter of human-produced CO₂, with the Southern Ocean alone accounting for roughly 40 percent of that amount. This makes it one of the planet’s most critical regions for slowing global warming. The Southern Ocean’s unique circulation patterns, where deep waters rise to the surface, exchange gases with the atmosphere, and then sink again carrying newly absorbed CO₂ into the depths, creates this powerful carbon sink effect.

Analysts suggest the paradox emerged because climate models predicted strengthening westerly winds would push more carbon-rich deep water to the surface, limiting the ocean’s ability to absorb additional human-produced CO₂. However, observational data from recent decades has shown no reduction in its capacity as a carbon sink.

Freshwater Creates Protective Barrier

Sources indicate that the answer lies beneath the surface. Dr. Léa Olivier, AWI oceanographer and lead author of the study, explains that their research examined biogeochemical data from Southern Ocean expeditions between 1972 and 2021. “We were able to determine that, since the 1990s, the two water masses have become more distinct from one another,” she stated.

The study reveals that increased freshwater from precipitation and melting glaciers and sea ice has reduced surface water salinity. This “freshening” reinforces the density stratification between surface and deep water masses, keeping CO₂-rich deep water trapped in the lower layer and preventing it from reaching the surface.

Temporary Solution With Risks

According to the analysis, this fresher surface water has temporarily offset the weakening of the carbon sink that model simulations predicted. However, researchers warn this situation could reverse as the strengthening westerly winds push deep water approximately 40 meters closer to the surface since the 1990s.

“As the transition layer between surface and deep water moves closer to the surface, it becomes more susceptible to mixing,” the report states. Such mixing would release the CO₂ that had accumulated beneath the surface water layer, potentially reducing the Southern Ocean’s capacity to absorb anthropogenic CO₂ and further driving climate change.

Critical Need for Winter Data

Professor Alexander Haumann, co-author of the study, emphasizes that additional data is needed, particularly from winter months when water masses tend to mix more extensively. “To confirm whether more CO₂ has been released from the deep ocean in recent years, we need additional data,” he explained.

The AWI plans to examine these processes more carefully through the international Antarctica InSync program, aiming to better understand climate change effects on the Southern Ocean and potential interactions. Researchers stress the importance of looking beyond the ocean’s surface to fully comprehend these complex processes and their implications for global climate patterns.

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