Scientists Shed Light on the Mysterious ‘Cold Blob’ in the North Atlantic Amid a Search for Its Cause
In two recent studies, researchers suggest a weakening ocean current system is to blame for a persistent cold spot in the Atlantic Ocean, though other factors may also be at play
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Just south of Greenland, in the northern Atlantic Ocean, a strange area of water has been confounding scientists for years. While the rest of the ocean warms, that patch has been mysteriously cooling. Researchers have offered different theories behind this “cold blob,” such as changes in ocean circulation patterns or aerosol pollution in the atmosphere.
Now, two recent studies are shedding more light on the phenomenon, adding to existing evidence that the slowdown of a key ocean current system is producing the cool region.
The cold blob—also known as a warming “hole”—can be spotted on maps of Earth’s changing surface temperature, appearing as a blue dot of cooling in a sea of red heat. As the water around it warms, the blob’s temperature has been steadily dropping by up to 0.5 degrees Fahrenheit.
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Researchers at the University of California, Riverside (UCR), looked at 20 years of observations of the Atlantic Meridional Overturning Circulation (AMOC), a system of ocean currents that circulate in the Atlantic Ocean. Then, they used 100 years of temperature and salinity data to reconstruct the ocean dynamics from before official records began. They published their work in the journal Communications Earth & Environment in May.
“People have been asking why this cold spot exists,” co-lead author Wei Liu, a climate scientist at UCR, says in a statement. “We found the most likely answer is a weakening AMOC.”
The AMOC acts like a water conveyor belt. It transports warm, salty water from the tropics to the North Atlantic, where the water cools, becomes more dense and sinks. That cooler water then travels south, continuing the cycle. However, research suggests the AMOC has been slowing down over the last century, because excess freshwater from melting ice in Greenland is making the water less dense, reducing the southward flow.
This is “a weakening of a major part of the climate system,” David Thornalley, a paleoceanographer at University College London who was not involved in the recent work, writes in an email to Perri Thaler at Live Science. Two years ago, a pair of scientists warned that climate change could lead the AMOC to collapse during this century.
Need to know: Melting of the Greenland Ice Sheet
The Greenland Ice Sheet is the largest mass of ice in the Northern Hemisphere, and it’s melting rapidly, losing mass at a rate of about 267 billion tons per year.
The UCR team compared the long-term records of the ocean to various climate models and found that only models simulating a slowdown of the AMOC aligned with the real-world conditions at the cold blob.
“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,” study co-lead author Kai-Yuan Li, a researcher at UCR, says in the statement. “It’s a very robust correlation.”
While the UCR scientists name ocean slowdown as the main cause for the cold blob, a new paper by researchers at Penn State University suggests the ocean and the atmosphere contribute equally. Their findings were published in the journal Science Advances on June 30.
In their study, the Penn State team writes that a weakened AMOC is linked not only to a slowdown of the water conveyor belt, but also to colder, drier conditions in the lower atmosphere. Above the cold blob, lower temperatures lead to less evaporation—and because water vapor has a warming effect on the atmosphere, a reduced amount of water vapor will lead to further cooling.
“Reducing the greenhouse effect, to put it simply, will feed back to the surface and amplify the pre-existing cold anomaly,” Yifei Fan, a graduate student at Penn State and lead author of the study, explains in another statement. “And on a longer time scale, this feedback can make the cold blob more persistent.”
As a result, this drop in heat from the atmosphere, along with oceanic processes, both keep the blob cool, the researchers say.
Scientists want to understand the cold blob because of its possible climate impacts, says Laifang Li, an atmospheric scientist at Penn State and study co-author, in the statement. Further research on the warming hole and the AMOC can help scientists build better climate predictions.
“The cold blob can disturb the atmospheric jet stream and storm activities, so it has implications for extreme weather events in North America and Europe,” adds Li.
