Although optimistic, recent research indicates that the Southern Ocean remains highly effective in absorbing carbon dioxide (CO₂). That’s still the case, despite the drastic changes to the lake’s salinity and overall climate conditions. This rich marine ecosystem has experienced one of the largest declines in surface water salinity. The prime culprit is the increasing freshwater input from extreme precipitation and rapid land-based glacier and sea-ice melting. Human connection The Southern Ocean plays a critical role in actively sequestering carbon. This process substantially delays the release of CO₂ into the atmosphere.
These realizations have huge implications. Climate change is quickly changing the fate of the Southern Ocean and impacting its current status as a carbon sink. Since the 1990s, scientists have been sounding alarms about a major change in the upper limit of deep water masses. It has advanced nearly 130 feet toward the surface. That’s a big change. It indicates that CO₂-rich water has been slowly but surely replacing the historically low-salinity winter surface water.
Changes in Salinity and Carbon Sequestration
The Southern Ocean’s surface water is losing salinity. This shift is due to the effects of more precipitation and extreme rainfall events, and increased glacial and sea ice melt. As these newfound freshwater sources multiply, they begin to make the salinity of the upper ocean more uniform. This low-salinity water has historically been effective at trapping carbon in deeper ocean layers, preventing its escape into the atmosphere.
The Southern Ocean’s role in sequestering carbon is complex and highly dependent on the region’s circulation patterns. Cold and often nutrient-rich water masses upwell from deeper levels and enrich the euphotic zone with cold, nutrient rich waters. This process is important for marine organisms and is an important driver of global climate patterns. Of course, that upwelled water is usually pretty darn old. It has spent hundreds or even thousands of years deep beneath the surface before it emerges once more to the surface.
Beyond ongoing warming and changes in salinity, the Southern Ocean appears to be retaining its ability to take up anthropogenic CO₂. Future warnings are not in sight. Current reality should not be misinterpreted as showing an imminent tipping point toward a diminishing ability of forests to absorb CO₂. The increasing enrichment of surface waters with nutrients may have in the immediate past compensated for some deteriorating trends, but carbon was still being sequestered.
Implications of Climate Change on Carbon Sink Functionality
As anthropogenic climate change continues, changes in the physical and chemical state of the Southern Ocean are ever-more detectable. Increasing temperatures and salinity levels are compounding and interacting in ways that we need to examine more closely. These alterations can significantly affect the ocean’s overall ability to absorb CO₂. This phenomenon is not new — observational studies had previously observed strengthening winds across the region and attached the cause to human-induced climate change.
These strengthening winds may additionally tip ocean circulation patterns, possibly boosting stratification even more. If that occurs, fewer CO₂-rich deep waters will make it up to the surface. Consequently, the Southern Ocean’s capacity to serve as a carbon sink will collapse. This kind of feedback loop would be particularly dangerous. Lower absorption capacity increases atmospheric CO₂ concentration, which subsequently exacerbates climate change, making this a vicious cycle.
Previous research showed that deep, old water in the Southern Ocean usually lives farther down, below about 200 meters. Deep water is essential to the global cycling of carbon. It contains nearly 40% of all carbon ever measured in ocean systems. It’s important to know how a changing surface salinity might be impacting our deep water. This newfound understanding will allow us to better gauge our future potential to absorb carbon.
Future Directions for Research
The continued study of the Southern Ocean’s dynamics underscores the importance of long-term observation and analysis. Scientists aim to better understand how the interplay between natural and anthropogenic factors influences carbon sequestration in this critical region. Future studies should monitor changes in salinity, temperature, and changes in ocean circulation to better understand these impacts. Our research will provide a sharper picture of how those factors will make or break the Southern Ocean’s contribution to slowing climate change.