Major reversal in ocean circulation detected in the Southern Ocean, with key climate implications

[-]

eeeking@reddit

At first, this sounded really alarming, but going to the original article on PNAS, it isn't quite as awful. Still bad, but perhaps not catastrophic, yet.... this phenomenon has been previously observed. Here's the abstract:

Abstract

For decades, the surface of the polar Southern Ocean (south of 50°S) has been freshening—an expected response to a warming climate. This freshening enhanced upper-ocean stratification, reducing the upward transport of subsurface heat and possibly contributing to sea ice expansion. It also limited the formation of open-ocean polynyas. Using satellite observations, we reveal a marked increase in surface salinity across the circumpolar Southern Ocean since 2015. This shift has weakened upper-ocean stratification, coinciding with a dramatic decline in Antarctic sea ice coverage. Additionally, rising salinity facilitated the reemergence of the Maud Rise polynya in the Weddell Sea, a phenomenon last observed in the mid-1970s. Crucially, we demonstrate that satellites can now monitor these changes in real time, providing essential evidence of the Southern Ocean’s potential transition toward persistently reduced sea ice coverage.

[-]

velocitivorous_whorl@reddit

Yes, agreed. The real question is “why is the Southern Ocean getting saltier when we expect it to be freshening as a result of climate change?” It’s entirely possible that this is a transient phenomenon, or — since it was last observed in the 1970s — that there is multi-decadal variability associated with the emergence of these polynynas.

[-]

Otto_Von_Waffle@reddit

Yeah, climate science (water current science, and many other climate adjacent science as well) is fairly new and barely understood.

Remember reading an article that some scientists were positing that California climate has been incredibly gentle and humid for the past 200-300 years and what we are seeing right now is a return to normal temperature/precipitation combined with global warming which is why California is turning into literal hell on earth

[-]

wet_suit_one@reddit

And so it begins...

It's fascinating how Homo colossus' unguided and uncontrolled activities are going about terraforming this world.

It will be really interesting to see where things end up. Sadly I won't live long enough to see it, but generations from now, assuming the records of the present persist as well as those of intervening time periods, the differences and changes will be able to be observed.

Here's hoping the unplanned future isn't too hellish. We only barely know what we're doing now and we have, effectively, no control over it. Like the creatures that transformed the atmosphere from a reducing one to an oxidative one, we're going to radically change this world of ours. It's going to be utterly amazing (kinda shit to live through, but times of great change usually are).

Just totally fascinating.

One our climate positve feedback loops really kick in (they might have already, it's not clear), boy oh boy are things gonna get wild!

What a time to be alive!

[-]

empleadoEstatalBot@reddit

Major reversal in ocean circulation detected in the Southern Ocean, with key climate implications

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.

This discovery was made possible thanks to a key technical breakthrough developed by the Barcelona Expert Center (BEC), a laboratory of ICM-CSIC specialized in satellite ocean observation. Until now, the Southern Ocean region was virtually inaccessible to satellites due to its low temperatures and the complex, ever-changing dynamics of sea ice. As a result, the BEC team developed a new data processor for the European SMOS satellite, tailored to the geographical and climatic variability of the polar environment.

“The new processor has allowed us to obtain surface salinity data of unprecedented quality in this region,” explains Verónica González. “Thanks to this improvement, we can now provide a coherent explanation for the rapid Antarctic sea ice loss that had puzzled the scientific community.”

The study not only provides a key piece in the climate change puzzle, but also redefines the role of the Southern Ocean in the global climate system. The SMOC plays an essential role in regulating the planet’s heat and carbon. Its disruption could trigger cascading effects on other circulation systems such as the AMOC, with potential consequences for the climate in Europe and other regions.

Aware of the urgent need to better understand these processes, BEC has launched two new ESA-funded projects in 2025: ARCTIC-FLOW, focused on the study of freshwater and density fluxes in the Arctic Ocean, and the climate change initiative CCI OSHF (Ocean Surface Heat Flux), dedicated to analyzing heat fluxat the ocean surface. Both projects aim to develop new satellite methodologies that will be key to monitoring, understanding, and anticipating the effects of accelerated climate change.

“The planet is sending us increasingly clear signals that we are crossing critical thresholds,” concludes Estrella Olmedo. “And in this case, it has done so from a remote corner of the world that is very difficult to monitor: the Southern Ocean. Thanks to satellites and cutting-edge observation tools, we can now see what was once invisible.”

Maintainer | Source Code | Stats

[-]