New Research Solves 100-Year Mystery of the Atlantic’s “Cold Blob”

By U. of California - Riverside. Nov. 15, 2025
https://scitechdaily.com/new-research-solves-100-year-mystery-of-the-atlantics-cold-blob/

New research shows that a long-debated cold patch near Greenland is linked to a weakening Atlantic circulation system. By matching a century of ocean data with climate models, scientists uncovered signs of a long-term slowdown with major implications for weather, ecosystems, and future climate change.
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Research confirms that a weakening circulation is driving the South Greenland anomaly.

For more than 100 years, a persistent pocket of unusually cold water south of Greenland has stood out against the steady warming of the Atlantic Ocean. This feature has sparked scientific debate, and a new study now points to its underlying cause: a long-term decline in a key ocean circulation system.

Researchers at the University of California, Riverside report that only one factor can account for the patterns seen in both ocean temperature and salt levels. Their analysis shows that the Atlantic Meridional Overturning Circulation, or AMOC, has been slowing down. This large system of currents influences global climate by carrying warm, salty water toward the north and returning cooler, deeper water toward the south.

“People have been asking why this cold spot exists,” said UCR climate scientist Wei Liu, who led the study with doctoral student Kai-Yuan Li. “We found the most likely answer is a weakening AMOC.”

The AMOC functions much like a conveyor belt, transporting heat and salt from the tropics into the North Atlantic. When this circulation weakens, less warm and salty water reaches the sub-polar region, producing the cool and fresh conditions observed near southern Greenland.

A reduced flow means that smaller amounts of heat and salt enter the North Atlantic, which creates cooler and less saline surface waters. This relationship is why scientists can use salinity and temperature measurements to assess the strength of the AMOC.
 

Reconstructing a Century of Change

Liu and Li examined temperature and salinity records covering roughly 100 years, since direct measurements of the AMOC have only been available for about two decades. Using these long-term datasets, the researchers pieced together how the circulation has changed over time and then tested their reconstruction against nearly 100 climate models. 


According to the paper published in Communications Earth & Environment, only the models that depicted a weakened AMOC successfully aligned with the observed data. Simulations that relied on a stronger circulation were unable to reproduce what is actually happening in the ocean.

“It’s a very robust correlation,” Li said. “If you look at the observations and compare them with all the simulations, only the weakened-AMOC scenario reproduces the cooling in this one region.”

Atlantic sea surface temperature trend between 1900-2005 (color shading in °C) for the average of six
observation datasets.
Credit: Kai-Yuan Li/UCR

The study also found that the weakening of the AMOC correlates with decreased salinity. This is another clear sign that less warm, salty water is being transported northward.

The consequences are broad. The South Greenland anomaly matters not just because it’s unusual, but because it’s one of the most sensitive regions to changes in ocean circulation. It affects weather patterns across Europe, altering rainfall and shifting the jet stream, which is a high-altitude air current that steers weather systems and helps regulate temperatures across North America and Europe.

The slowdown may also disturb marine ecosystems, as changes in salinity and temperature influence where species can live.
 

A Debate Resolved

This result may help settle a dispute amongst climate modelers about whether the South Greenland cooling is driven primarily by ocean dynamics or by atmospheric factors such as aerosol pollution. Many newer models suggested the latter, predicting a strengthened AMOC due to declining aerosol emissions. But those models failed to recreate the actual, observed cooling.

“Our results show that only the models with a weakening AMOC get it right,” Liu said. “That means many of the recent models are too sensitive to aerosol changes, and less accurate for this region.”

By resolving that mismatch, the study strengthens future climate forecasts, especially those concerning Europe, where the influence of the AMOC is most pronounced.

The study also highlights the ability to draw clear conclusions from indirect evidence. With limited direct data on the AMOC, temperature and salinity records provide a valuable alternative for detecting long-term change, and for helping to predict future climate scenarios.

“We don’t have direct observations going back a century, but the temperature and salinity data let us see the past clearly,” Li said. “This work shows the AMOC has been weakening for more than a century, and that trend is likely to continue if greenhouse gases keep rising.”

As the climate system shifts, the South Greenland cold spot may grow in influence. The hope is that by unlocking its origins, scientists can better prepare societies for what lies ahead.

“The technique we used is a powerful way to understand how the system has changed, and where it is likely headed if greenhouse gases keep rising,” Li said.

 

 

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