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For more than 100 years, scientists have noticed something odd in the North Atlantic Ocean. South of Greenland, there is a patch of ocean water that stays cooler than the rest of the world’s warming seas. This area is now known as the North Atlantic Warming Hole, or NAWH.
A Strange Patch in the Ocean
While most oceans are heating up due to climate change, this cold spot has puzzled experts for decades. Why hasn’t this region followed the same warming pattern as the rest of the planet?
Recently, new research has revealed an important clue. Scientists believe that a weakening ocean current is behind this chilly mystery. This current is called the Atlantic Meridional Overturning Circulation, or AMOC. It plays a big role in moving warm water from the tropics to the north and sending cooler water back down south.
The AMOC acts like a giant conveyor belt in the ocean. When it slows down, it can cause big changes in ocean temperature and salt levels. The new study found that the AMOC has been getting weaker for more than 100 years, and that might be why the cold patch has formed.
What Happens When the Current Slows?
The AMOC is a powerful force in the ocean. It moves warm, salty water northward and pushes cold water back south. This movement helps control the climate in places like Europe and North America.
But when the AMOC slows down, less heat and salt reach the northern waters. This causes the area south of Greenland to become cooler and fresher. Scientists used many years of sea surface temperature and salt level data to study this pattern. They also used over 90 climate models to test what might be happening.
Only the models that showed a slowing AMOC were able to create the same cooling pattern that scientists observed in real life. These models showed a slow drop in temperature of about 0.3°C (about 0.54°F) per 100 years in the region.
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The researchers also looked at deeper parts of the ocean. They discovered that the cold spot doesn’t just affect the surface. It stretches down to 3,000 meters below the sea. That means the slowdown is impacting the whole column of water — from top to bottom.
They found that when the AMOC weakens, a gap forms where warm water normally flows. This heat gap leads to cooler water between 40°N and 65°N — the exact area where the cold spot is located. The salt levels also change, with more freshwater sitting on the ocean’s surface. This freshening trend was strongest in the North Atlantic Warming Hole and reached into the Labrador Sea.
To track the AMOC, scientists created “fingerprints” — special patterns that show up when the current weakens. These fingerprints include cooler temperatures and lower salt levels in certain areas. They found strong links between these patterns and the signs of a slowing AMOC.
Other Theories Don’t Add Up
In the past, some experts thought the cold spot might be caused by wind patterns or even by lower air pollution. But these ideas didn’t hold up when tested.
To figure this out, scientists used two different types of climate models. The first type only looked at the atmosphere, without real ocean currents. In these models, the cold patch didn’t appear. But in the second type — which included real ocean circulation — the cold spot clearly formed.
This means that the cold water patch is not caused by air changes alone. It needs the ocean current, specifically the AMOC, to explain what’s happening.
The cold spot doesn’t just change the ocean. It can also affect the jet stream — the fast-moving air current high above us — and impact weather across continents. It may bring colder winters or wetter summers in some places.
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Another concern is the effect on sea life. Many fish and marine animals depend on certain temperatures and salt levels to survive. When those conditions shift, it can change where they live or how they grow.
This new study shows that only the models with a slowing AMOC can recreate the cold spot. That means some other climate models may be too focused on pollution levels and not paying enough attention to how the ocean is changing.
By using detailed temperature and salinity records, scientists now have a better picture of what’s happening in the Atlantic. This cold patch isn’t just a strange mystery anymore — it’s a clear sign of something much bigger happening deep beneath the waves.
