Southern Ocean’s Carbon ‘Burp’ Threatens Climate Stability, New Study Finds

Southern Ocean’s Carbon ‘Burp’ Threatens Climate Stability, New Study Finds

The Southern Ocean, a critical global climate regulator, may be far less stable in its ability to absorb atmospheric carbon dioxide (CO2) than previously understood. New research, published in Science, reveals significant year-to-year fluctuations in the ocean’s CO2 uptake, raising concerns that it could intermittently “burp” stored carbon back into the atmosphere, potentially accelerating global warming.

This groundbreaking study, utilizing advanced robotic ocean sensors, challenges long-held assumptions about the Southern Ocean’s consistent role as a carbon sink. It highlights a complex interplay between ocean dynamics and atmospheric patterns that could have profound implications for future climate predictions.

The Ocean’s Vital Role in Climate Regulation

For decades, the world’s oceans have provided an invaluable service to humanity, absorbing approximately one-quarter of all anthropogenic CO2 emissions and over 90% of the excess heat generated by these emissions. This massive absorption capacity has significantly mitigated the pace of global warming, preventing even more drastic climate shifts.

Among all ocean basins, the Southern Ocean stands out as particularly crucial. It accounts for roughly 40% of the total oceanic CO2 uptake, making it the single most important oceanic region for buffering atmospheric carbon. Its cold, nutrient-rich waters are highly efficient at dissolving CO2 from the atmosphere and transporting it into the deep ocean, effectively locking it away for centuries.

Unveiling the “Burp”: New Research and Argo Floats

Until recently, accurately measuring the Southern Ocean’s carbon dynamics on a year-to-year basis was a formidable challenge. Traditional methods, like ship-based surveys, offer only snapshots in time and space. However, a new generation of Argo floats, robotic ocean profilers equipped with sophisticated biogeochemical sensors, has revolutionized this field.

This study, led by Dr. Peter Landschützer from the University of Liège in Belgium and co-authored by Professor Richard Matear of CSIRO in Australia, analyzed data collected by these advanced floats between 2014 and 2020. These floats autonomously drift through the ocean, repeatedly diving from the surface down to 2,000 meters and transmitting valuable data on pH, oxygen, and other parameters back to satellites.

This continuous, deep-ocean data allowed scientists to observe interannual variability – significant year-to-year changes – in the Southern Ocean’s carbon absorption. They discovered that in some years, the ocean absorbed more CO2 than expected, while in others, its uptake was significantly reduced, or it even released CO2 back into the atmosphere. This release is what scientists refer to as an oceanic “burp.”

“Our research shows that the Southern Ocean’s capacity to absorb CO2 is not a constant, steady process. It fluctuates significantly from one year to the next, influenced by powerful natural climate patterns,” stated Dr. Landschützer.

The Southern Annular Mode Explained

The key driver behind this newly observed variability is the Southern Annular Mode (SAM). SAM is a major climate pattern that describes the north-south movement of the westerly wind belt that encircles Antarctica. It has two primary phases:

• Positive SAM Phase: The westerly winds shift southward, closer to Antarctica. These stronger, more southerly winds enhance the mixing of surface waters, bringing more CO2-poor water to the surface which can then absorb more atmospheric CO2. This typically leads to increased CO2 uptake by the Southern Ocean.
• Negative SAM Phase: The westerly winds shift northward, away from Antarctica. This reduces the efficiency of CO2 absorption, and in some cases, can lead to a net outgassing of CO2 from the ocean back into the atmosphere.

Previous climate models and satellite observations struggled to fully capture this intricate relationship and the resulting interannual variability. The detailed, subsurface data from the Argo floats provided the crucial missing link, offering an unprecedented look at how SAM directly impacts the ocean’s carbon cycle.

Implications for a Warming Planet

The findings underscore the fragility of the Southern Ocean’s role as a reliable carbon sink. If the Southern Annular Mode were to enter a prolonged negative phase, or if other climate feedbacks were to weaken the ocean’s absorption capacity, the consequences could be severe:

• Accelerated Warming: A reduced oceanic carbon uptake, or worse, a net release of CO2, would mean more greenhouse gases remain in the atmosphere, directly accelerating global warming.
• Challenges for Climate Models: The newly identified variability adds another layer of complexity to climate projections. Accurate predictions of future warming will require models that can precisely account for these dynamic ocean-atmosphere interactions.
• Urgency of Emissions Reduction: This research reinforces the critical need for aggressive and sustained reductions in anthropogenic CO2 emissions. Relying on natural carbon sinks to continuously buffer our emissions is a risky strategy, as their capacity can fluctuate and potentially diminish.

The Path Forward: More Data, Better Understanding

The study highlights the immense value of the Argo program, which has been collecting vital oceanographic data since 2000. However, the number of Argo floats equipped with biogeochemical sensors, while growing, is still relatively small—only around 200 globally. To fully understand and predict the Southern Ocean’s future carbon dynamics, a significant expansion of this observational network is essential.

Increased deployment of these advanced floats will provide scientists with the comprehensive, real-time data needed to refine climate models, improve our understanding of ocean-atmosphere feedback loops, and ultimately, better anticipate the trajectory of global climate change.

Key Takeaways

• Southern Ocean’s Critical Role: It absorbs approximately 40% of the ocean’s total CO2 uptake, significantly slowing global warming.
• New Variability Discovered: Recent research shows the Southern Ocean’s CO2 absorption fluctuates significantly year-to-year, sometimes even releasing CO2 (a “burp”).
• Southern Annular Mode (SAM): This atmospheric pattern is the primary driver of these fluctuations, influencing westerly winds and ocean mixing.
• Argo Float Technology: Advanced robotic floats with biogeochemical sensors provided the crucial data for this discovery, offering unprecedented subsurface insights.
• Climate Implications: This variability could accelerate global warming if the ocean’s capacity to absorb CO2 diminishes, posing new challenges for climate predictions.
• Need for More Data: Expanding the network of biogeochemical Argo floats is vital for better understanding and predicting future climate scenarios.

What’s Next

Scientists will continue to monitor the Southern Ocean’s carbon dynamics closely, with efforts focused on deploying more biogeochemical Argo floats to build a denser, more continuous dataset. This expanded data will be crucial for integrating these findings into global climate models, enabling more accurate long-term predictions and informing international climate policy discussions throughout 2025 and beyond.