Shifting Patterns in the Southern Ocean’s Carbon Absorption
The Southern Ocean plays a critical role in the Earth’s carbon cycle, yet climate change is altering its function as a carbon sink. Despite anticipated reductions in its CO₂ absorption capacity, recent findings reveal a more complex situation beneath the ocean’s surface.
Research conducted by the Alfred Wegener Institute sheds light on how the Southern Ocean continues to absorb substantial amounts of carbon dioxide, contrary to model predictions suggesting a decline. This study, published in Nature Climate Change, delves into the mechanisms maintaining this oceanic carbon storage despite climate-induced disruptions.
The Southern Ocean is responsible for storing around 40% of human-generated CO₂ absorbed by the world’s oceans, making it a key player in mitigating global warming. The process involves deep ocean waters, which are rich in natural CO₂, rising to the surface and exchanging gases with the atmosphere. However, as climate change intensifies, the dynamics of this process are shifting.
According to Dr. Léa Olivier, a leading oceanographer at AWI, “Deep water in the Southern Ocean is normally found below 200 meters. It is salty, nutrient-rich, and relatively warm compared to water nearer the surface.” This water, laden with CO₂, returns to the surface through upwelling, yet its interaction with surface waters is changing.
Freshwater Influence and Climate Change
Recent observations indicate that the surface waters of the Southern Ocean are becoming less salty due to increased freshwater inputs from precipitation and melting ice. This “freshening” creates a stronger density barrier, preventing CO₂-rich deep waters from reaching the surface.
Olivier explains, “Our study shows that this fresher surface water has temporarily offset the weakening of the carbon sink in the Southern Ocean.” This effect, however, is not permanent and could reverse if the stratification weakens.
Strengthening westerly winds, another consequence of climate change, are causing the deep water masses to rise closer to the surface, potentially leading to increased CO₂ release. These winds have already shifted the upper boundary of deep water closer to the surface by approximately 40 meters since the 1990s, raising concerns about future carbon absorption capacities.
“What surprised me most was that we actually found the answer to our question beneath the surface. We need to look beyond just the ocean’s surface, otherwise we run the risk of missing a key part of the story,” states Olivier. Further research is underway to closely monitor these changes and their implications for global climate patterns.
For more insights, the Alfred Wegener Institute is part of the international Antarctica InSync program, aiming to deepen the understanding of these complex processes and their broader impacts on climate change.
Original Story at phys.org