Satellite data processing algorithms developed by ICM-CSIC have played a crucial role in detecting this significant shift in the Southern Hemisphere, which could accelerate the effects of climate change.

Thanks to data obtained from Earth observation satellites, an international team of scientists has detected an unprecedented phenomenon for the first time: a reversal in the ocean circulation of the Southern Ocean. The study, led by the National Oceanographic Center (NOC, United Kingdom), was recently published in the journal PNAS. The Institut de Ciències del Mar (ICM-CSIC) played a fundamental role in the research by developing a set of pioneering satellite observations within the framework of the SO-FRESH project, funded by the European Space Agency (ESA).

The study’s main finding is both surprising and alarming: since 2016, a sustained increase in surface salinity has been detected in the region between the polar and subpolar gyres of the Antarctic Ocean. This change in water composition suggests that the deep ocean circulation in the Southern Hemisphere—known as the SMOC—is not only being altered, but has reversed. That is, instead of sinking into the depths, surface water is being replaced by deep water masses rising to the surface, bringing with them heat and carbon dioxide (CO₂ ) that had been trapped for centuries.

“We are witnessing a true reversal of ocean circulation in the Southern Hemisphere—something we’ve never seen before,” explains Antonio Turiel, ICM-CSIC researcher and co-author of the study. “While the world is debating the potential collapse of the AMOC in the North Atlantic, we’re seeing that the SMOC is not just weakening, but has reversed. This could have unprecedented global climate impacts.”

According to the research team, the consequences of this reversal are already becoming visible. The upwelling of deep, warm, CO₂-rich waters is believed to be driving the accelerated melting of sea ice in the Southern Ocean. In the long term, this process could double current atmospheric CO₂ concentrations by releasing carbon that has been stored in the deep ocean for centuries—potentially with catastrophic consequences for the global climate.

https://www.icm.csic.es/en/news/major-reversal-ocean-circulation-detected-southern-ocean-key-climate-implications