New research led by the University of East Anglia (UEA) has brought a hopeful perspective to the complex interplay between the Antarctic ozone hole and the carbon uptake capacity of the Southern Ocean. Through advanced modeling and detailed simulations, the study reveals that the detrimental effects of the ozone hole on the ocean’s ability to absorb atmospheric carbon dioxide are reversible—but this reversal crucially depends on a substantial and rapid reduction in global greenhouse gas emissions. The findings provide new insights into how atmospheric chemistry and oceanic processes are entangled, highlighting a dynamic balance that could shift as humanity’s climate choices unfold.
The Southern Ocean, encircling Antarctica, plays an outsized role in the global carbon cycle. Despite covering a relatively small fraction of the Earth’s surface, it accounts for a disproportionately large share of carbon dioxide absorption, acting as a crucial brake on the acceleration of human-driven climate change. Its unique circulation patterns, driven by strong circumpolar winds and deep mixing processes, bring carbon-rich waters to the surface where CO2 can be exchanged with the atmosphere. Understanding the factors that modulate this carbon sink is essential for projecting future climate trajectories.
In this comprehensive study, researchers from UEA and the UK’s National Centre for Atmospheric Science (NCAS) employed the UK Earth System Model (UKESM1) to dissect the competing influences of stratospheric ozone depletion and greenhouse gas (GHG) forcing on Southern Ocean circulation and carbon uptake. By simulating multiple scenarios spanning from the mid-20th century to the end of the 21st century, the team addressed how the wind-driven circulation, ocean stratification, and carbon distribution will evolve under different future conditions.
The research scrutinized three distinct ozone states: an idealized scenario in which the ozone hole never opened, a realistic scenario reflecting the observed depletion and gradual healing following the Montreal Protocol’s success in curbing ozone-depleting substances, and a hypothetical case where the ozone hole’s maximum size persisted throughout the 21st century. These ozone trajectories were paired with two greenhouse gas emission pathways—one representing low emissions in line with aggressive mitigation, and the other simulating continued high emissions.
A key finding is that the loss of stratospheric ozone in the late 20th century intensified the circumpolar westerly winds over the Southern Ocean. These stronger winds invigorated ocean upwelling, bringing carbon-rich deep waters to the surface. This process reduced the ocean’s capacity to absorb carbon dioxide because waters closer to the surface became saturated with carbon, diminishing the chemical gradient that drives CO2 uptake from the atmosphere. Thus, the ozone hole indirectly lessened the Southern Ocean carbon sink, undermining one of Earth’s crucial climate moderators.
However, as ozone levels recover—a process projected to occur over the coming decades thanks to international environmental policy—the study suggests the effects of ozone depletion on Southern Ocean winds and circulation will progressively weaken. The healing ozone layer should theoretically return wind patterns towards their historical state, reducing upwelling-induced carbon saturation at the surface and enhancing the ocean’s capacity to sequester atmospheric CO2 once again.
Yet, this optimistic outlook is tempered by the competing influence of rising greenhouse gas concentrations, which independently act to strengthen winds through different mechanisms, including atmospheric warming and altered temperature gradients. Under a high-emission future, the greenhouse gas forcing could sustain or even amplify the strong circumpolar winds, effectively negating the benefits of ozone recovery on carbon uptake. This interplay injects significant uncertainty into projections of the Southern Ocean carbon sink.
Furthermore, the authors’ analysis uncovers that the coupling between ocean circulation changes and carbon uptake efficiency will lessen over time. This diminishing influence stems from shifts in the vertical distribution of carbon within the ocean—a consequence of continual ocean warming and resultant stratification changes that reduce the ventilation of deeper waters. As carbon accumulates at depth, the capacity of circulation changes to impact surface carbon levels diminishes, altering the feedbacks between climate and the carbon cycle in the Southern Ocean.
Methodologically, the study leverages state-of-the-art Earth system modeling that integrates atmospheric chemistry, physics, and ocean biogeochemistry, enabling nuanced exploration of how coupled processes dictate carbon fluxes. The model’s simulations carefully isolate the effects of ozone evolution and greenhouse gas forcing, providing a clearer attribution of observed and projected changes to their respective drivers. This approach offers critical insights into the sometimes counteracting forces shaping the Southern Ocean’s role as a carbon sink.
Lead author Dr. Tereza Jarníková of UEA’s Tyndall Centre for Climate Change Research emphasizes that this research unmasks a complex yet hopeful narrative. “Our work shows that the anthropogenic impact via the ozone hole on Southern Ocean carbon uptake is not a one-way street. If strong greenhouse gas mitigation is pursued, the reversibility of ozone-driven wind changes could enable the ocean’s carbon sink to recover, partially restoring a vital Earth system feedback,” she explains.
These revelations underscore the delicate balance within the Earth system, where atmospheric chemistry and human emissions intersect to influence marine biogeochemistry and physical circulation. The study calls attention to the pivotal role of international policies like the Montreal Protocol, not only in healing the ozone layer but also in indirectly influencing global carbon cycles and climate stabilization.
As the 21st century unfolds, the Southern Ocean will continue to be a frontline for climate feedbacks. The research highlights that the future efficiency of this carbon sink is contingent not only on natural recovery processes but also on human decisions regarding greenhouse gas emissions. The complexity of these interactions necessitates continued, detailed observations and advanced modeling efforts to refine projections and guide policy.
In sum, this study provides a sophisticated and hopeful outlook on the Southern Ocean carbon sink’s trajectory amidst evolving atmospheric conditions. It signals that the recovery from ozone depletion is a key piece of the puzzle—but its positive effects on carbon uptake can only be fully realized in a world where greenhouse gas emissions are rapidly curtailed. This work contributes to a deeper understanding of the carbon-climate feedbacks critical for anticipating the Earth’s future under climate change.
Subject of Research: The impact of ozone hole depletion and its recovery, alongside greenhouse gas emissions, on the Southern Ocean circulation and its capacity to absorb atmospheric carbon dioxide.
Article Title: Decreasing importance of carbon-climate feedbacks in the Southern Ocean in a warming climate
News Publication Date: 16-May-2025
Web References:
https://research-portal.uea.ac.uk/en/persons/tereza-jarnikova
http://dx.doi.org/10.1126/sciadv.adr3589
References:
Jarníková, T., Le Quéré, C., Rumbold, S., Jones, C. (2025). Decreasing importance of carbon-climate feedbacks in the Southern Ocean in a warming climate. Science Advances. DOI: 10.1126/sciadv.adr3589
Keywords: Ozone hole, Southern Ocean, carbon uptake, greenhouse gases, atmospheric chemistry, ocean circulation, climate change, carbon sink, ozone recovery, Earth system model, climate feedbacks, Antarctic circulation
