For decades, computer models of climate change have predicted that as the Earth gets warmer, the water at the surface of the ocean becomes less salty — melting polar ice adds a lot of water to the system, but not the salt to go along with it. That prediction matched the observations scientists have recorded for decades.
But between 2015 and 2016, the trend unexpectedly reversed. The surface water around Antarctica in the Southern Ocean began getting more salty, not less.
On June 30, 2025, a team of researchers led by Alessandro Silvano at the University of Southampton released a report titled "Rising surface salinity and declining sea ice: A new Southern Ocean state revealed by satellites" in the peer-reviewed scientific journal
Less than a week later, an online newswire service misreported that Silvano's team had discovered that a current in the Southern Ocean had "reversed directions" for the first time in recorded history.
In an article titled "Southern Ocean current reverses for first time, signalling risk of climate system collapse," bne IntelliNews ostensibly summarized the study's findings for the public, which were then were copied and shared across social media, where many people believed the findings were accurately described.
But according to Silvano, who spoke to Snopes via Zoom, the framing of that news article was wholly incorrect — while his report did document a changing trend, it did not document an ocean current reversing direction.
(The sections below focus mostly on the study's findings of increased ocean salinity. Reduced sea ice and its potentially devastating climate impacts is also an important topic, but is not relevant to the claim in question).
What was the research actually about?
Up until 2014, according to Silvano, scientists had observed two trends in the Southern Ocean: fresher water, and perhaps counterintuitively, more sea ice (cold, fresh surface water slows circulation patterns that transfer heat to the ocean surface). But beginning in 2015, the trends flipped — sea ice dramatically decreased and the surface water got saltier. Scientists immediately noticed, but haven't quite figured out what caused the change.
"We've been thinking about these things for a long time now," Silvano said. "And something we started thinking about a couple of years ago was, 'can we use satellites to observe salinity from space?'"
They weren't the first to think of it — NASA and the European Space Agency have satellites that track sea salinity. However, there was problems using those satellites to observe polar regions. It was harder for the satellite signal to measure colder waters, and roaming pieces of sea ice could block the measurements.
Silvano's team was able to develop algorithms to sort through the noise, and the big changes in the Southern Ocean made for a natural testing ground. When the satellite data came back,
Indeed, the data showed saltier water at the surface, matching previous observations and proving that satellites could be used to measure surface salinity near the poles.
The paper never said anything about an ocean current reversal
However, the study didn't draw conclusions on why the surface water in the Southern Ocean was getting saltier, whether that trend would continue, or suggest that a Southern Ocean current had reversed completely.
One of the most insidious aspects of climate change is that it occurs on a scale that is longer than a human lifetime, even as human actions have rapidly increased how fast the Earth is warming. Silvano's team looked at 12 years of data for their research. He said a team would need "hundreds of years" of data in order to truly understand the patterns and draw conclusions.
The idea that a Southern Ocean current had completely reversed is a conclusion that simply can't be made off of 10 years of data. The only thing that had reversed in the last 10 years was a trend in the sea ice and the water salinity.
"Something that I'm really passionate about is the 'Why,'" Silvano said. "Ours was a report that showed [the salinity reversals], but we really still don't know why."
What is ocean salinity and why is it important?
Oceans cover about 70% of the planet, according to the U.S. Geological Survey, and as anyone who's been to an oceanic beach can tell you, that water is salty. However, salt in the ocean is not distributed evenly.
According to the National Oceanic and Atmospheric Administration, for instance, areas of the ocean that are rather enclosed and don't have a lot of fresh water sources feeding them, like the Mediterranean and Red Seas, are quite salty, or high in salinity. Oceans near the equator are less salty — lower in salinity — because that area of the planet receives more rain. And, as already mentioned, oceans near the poles also tend to be have fresher water because of melting ice.
But there's another key variable — depth. Saltier water is denser — heavier — and sinks down to the ocean floor, whereas warmer, fresher water sits near the surface.
Ocean salinity is therefore, one of the two key factors (alongside temperature), that creates deep ocean currents. When sea ice freezes, the salt stays in the ocean. The same amount of salt in less water makes the now-colder, saltier water sink, and warmer, fresher surface water must flow in to replace it. That water then cools down in turn, keeping the cycle going.
This process is called thermohaline circulation (thermo: temperature, haline: salinity), and the large, worldwide current it creates, sometimes nicknamed the "global conveyor belt," is essential in stabilizing the Earth's climate.
As an example, one part of that network, the North Atlantic Current that brings warmer waters to the west coast of Europe, is known for keeping temperatures on the continent higher than expected for those latitudes. It's also responsible for backfilling the cold, salty water in the Arctic that sinks to the ocean floor as part of the massive Atlantic meridional overturning circulation (AMOC) current, one of two main parts of the "global conveyor belt."
According to the misleading news report on the study, the AMOC's "Deep Western Boundary Current" had supposedly reversed. As previously explained, that idea was false.