UNIVERSITY PARK, Pa. — A peculiar phenomenon in the Atlantic Ocean, known as the “cold blob,” has puzzled scientists for years. Located just south of Greenland, this area is cooling while much of the world continues to warm. Researchers at Penn State have now identified that the weakening of the Atlantic Meridional Overturning Circulation (AMOC) affects both the ocean and the atmosphere, contributing equally to this anomaly.
The findings, published in the journal Science Advances, suggest that the cooling ocean also leads to a cooler, drier atmosphere, which in turn amplifies the cold anomaly. “In the past century, most of the planet has warmed while the subpolar North Atlantic has been stubbornly cooling,” said Pengfei Zhang, an assistant research professor at Penn State and co-author of the study. “Our findings help explain why this so-called cold blob exists and shed light on how future changes in ocean currents could ripple through the climate system.”
Understanding the Cold Blob
Previous studies have primarily focused on ocean currents that transport warm water to the North Atlantic. However, the new research highlights the atmospheric contributions to the cold blob. “We analyzed state-of-the-art climate models to quantify two pathways for how the AMOC contributes to the cold blob,” explained Yifei Fan, the study’s lead author. “And we found that the contribution from the atmosphere is comparable to that from ocean transport itself, which has never been found before.”
The AMOC functions like an ocean conveyor belt, bringing warm, salty water from the tropics to the North Atlantic, where it cools, becomes denser, and sinks. This process is crucial for regulating global climate. However, the influx of freshwater from the melting Greenland Ice Sheet dilutes the salty ocean water, making it less dense and less able to sink, thereby weakening the conveyor belt.
Atmospheric Feedback Loop
Fan noted that cooler ocean surface temperatures reduce evaporation and atmospheric moisture, which means less water vapor—a greenhouse gas that traps heat—is present. “Reducing the greenhouse effect, to put it simply, will feed back to the surface and amplify the pre-existing cold anomaly,” Fan said. “And on a longer time scale, this feedback can make the cold blob more persistent.”
The researchers employed advanced global climate models and a diagnostic tool called a partial temperature decompositional framework to investigate the physical processes linking the AMOC to the cold blob. This approach revealed the atmospheric feedback as more significant than previously realized.
“Usually, people think about why this cold blob occurs and their very natural, intuitive thought is to look for the oceanic contribution,” said Laifang Li, assistant professor of meteorology and atmospheric science at Penn State. “We ask the question, why can’t the AMOC influence the cold blob through other processes? And I think that is a philosophical novelty to this study.”
Implications for Climate and Weather
Understanding the cold blob is crucial due to its potential impact on climate patterns. “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,” Li added. The study’s findings are based on climate models, which, while accurate, are not perfect representations of reality. Future research is needed to confirm the extent to which the two pathways contribute to the cold blob.
The research team included Eugene Clothiaux, professor of meteorology at Penn State, and Duo Chan, assistant professor at the University of Southampton, UK. The study was supported by NASA and the U.S. National Science Foundation.
The Broader Context of Climate Research
At Penn State, researchers are tackling real-world problems that affect the health, safety, and quality of life globally. For decades, federal support for research has driven innovations that enhance national security, industrial competitiveness, and economic strength. However, recent federal funding cuts threaten this progress.
As scientists continue to unravel the complexities of climate phenomena like the cold blob, the need for sustained research funding becomes ever more critical. The outcomes of such studies not only deepen our understanding of climate systems but also inform policy and preparedness for future climate-related challenges.
