A Troubling Signal from the North Atlantic
A massive system of swirling ocean currents in the North Atlantic — known as the subpolar gyre — is showing unusual and unstable behavior that may indicate it’s approaching a climate tipping point, according to new research published in Science Advances.
By studying the chemistry locked inside clam shells, scientists have reconstructed 150 years of ocean history and found that the gyre has destabilized twice in the modern era: once around 1920, and again from 1950 to the present.
“It’s highly worrying,” says Dr. Beatriz Arellano Nava, lead author and postdoctoral research fellow at the University of Exeter. “We still need to understand more of the impacts of a subpolar gyre weakening. But what we know so far is that it would bring more extreme weather, particularly in Europe — and alter global rainfall patterns.”
What Is the Subpolar Gyre—and Why Does It Matter?
The North Atlantic subpolar gyre is a vast system of rotating ocean currents that sits just south of Greenland.
It forms part of the larger Atlantic Meridional Overturning Circulation (AMOC) — a global conveyor belt of water that distributes heat from the tropics to the northern latitudes.
This circulation system regulates the weather across the Northern Hemisphere. It influences everything from European winters and Atlantic hurricanes to African monsoons and Amazon rainfall.
If it slows down or collapses, the results could include:
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Colder, stormier winters in northern Europe
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Drought in parts of Africa and South America
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Shifts in marine ecosystems and fish populations
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Rising sea levels along the U.S. East Coast
How Clam Shells Tell Ocean Stories
To understand long-term ocean behavior, Arellano Nava and her team turned to an unexpected archive: clams.
Two species — Arctica islandica and Glycymeris glycymeris — live for centuries, building growth rings in their shells that record environmental changes much like tree rings.
By analyzing 25 datasets of isotopic ratios (like oxygen-18) from these shells, the team reconstructed year-by-year variations in ocean conditions.
“With clam records, we have that nice dating for each layer,” Arellano Nava explained.
“They are like the tree rings of the ocean.”
Two Alarming Periods of Instability
The clam data revealed two clear signals of instability in the North Atlantic subpolar gyre:
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Around 1920, coinciding with the North Atlantic regime shift, a period of abrupt climate reorganization occurred.
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From 1950 to today, suggesting a long-term loss of stability that continues to intensify under modern climate change.
The 1920s event likely reflected the gyre’s recovery from its collapse during the Little Ice Age (13th–19th centuries), when weaker ocean circulation contributed to centuries of cooler temperatures in Europe and North America.
The current signal, however, is more troubling — a gradual weakening that could soon cross a tipping threshold.
A Tipping Point Within Reach?
The subpolar gyre and the AMOC are closely linked, but the gyre can destabilize independently, according to Arellano Nava.
A collapse of the gyre would produce regional effects similar to an AMOC shutdown, though on a smaller scale.
Cold, dense water sinking in the gyre’s center helps keep it spinning, but melting Greenland ice and warming oceans are diluting and warming this water, making it less dense and less able to sink.
If this continues, the system could weaken further — or even reorganize itself entirely.
“We don’t know exactly what the tipping point is,” Arellano Nava cautions.
“It could be the AMOC itself, but we may be observing a subpolar gyre weakening first, and that’s worrying.”
Skepticism and Scientific Debate
Not all experts are convinced that the clam data conclusively show a shift in gyre dynamics.
Professor David Thornalley of University College London notes that while the data are “very useful,” they don’t directly link the chemical patterns to measurable ocean features.
“I am skeptical about the interpretation,” Thornalley said.
“The datasets allow insights into climate changes on a year-by-year basis, but they don’t necessarily prove a shift in the subpolar gyre’s operation.”
Even so, most oceanographers agree that the North Atlantic is changing rapidly, and that continuous monitoring is essential for detecting early warning signs.
Lessons from the Past, Warnings for the Future
During the Little Ice Age, a slowdown in the North Atlantic’s circulation coincided with centuries of cooler, harsher climate.
Today, the situation is different — but the drivers of instability (melting ice, rising temperatures, and salinity changes) are even more intense.
If the gyre weakens further, Europe could face more extreme storms, shifts in rainfall, and unpredictable weather patterns — effects that may ripple worldwide through atmospheric and oceanic feedback loops.
Key Takeaway
The North Atlantic subpolar gyre — a vital engine in Earth’s climate — may be losing stability faster than expected.
While not yet catastrophic, these early warning signals show that even the ocean’s deepest systems are feeling the pulse of global warming.By Sascha Paré, Live Science
Adapted for DatalytIQs Academy Climate & Oceanography Blog
Published: October 3, 2025
Source: Science Advances (2025)
Image Credit: NASA’s Scientific Visualization Studio
References:
Arellano Nava, B. et al. (2025). Early warning signals of subpolar gyre destabilization revealed by North Atlantic bivalve records. Science Advances. DOI: 10.1126/sciadv.ady8347
NASA’s Scientific Visualization Studio imagery
