North Atlantic Subpolar Gyre Nears Tipping Point, Clam Study Reveals

The intricate dance of ocean currents in the North Atlantic is showing signs of unusual behavior, hinting at a potential tipping point. A recent study analyzing clam shells has brought this concern to light, raising questions about the stability of these essential oceanic systems.

The North Atlantic subpolar gyre, a crucial component in the heat transport mechanism to the Northern Hemisphere, is part of the larger Atlantic Meridional Overturning Circulation (AMOC). New findings suggest that since the 1950s, this gyre has been losing its stability, which might result in a significant weakening of its circulation in the near future. This was reported in a study published on October 3 in Science Advances.

“It’s highly worrying,” expressed Beatriz Arellano Nava, the study’s lead author and a postdoctoral research fellow at the University of Exeter, in a conversation with Live Science. Recognized as a tipping element, the subpolar gyre’s abrupt weakening could lead to extreme weather events in Europe and shifts in global precipitation patterns.

While the subpolar gyre is a branch of the AMOC, it can independently cross tipping points. The potential climate consequences for Europe, if the gyre weakens, could resemble those of an AMOC collapse but on a smaller scale, according to Arellano Nava. She warns that even without an AMOC collapse, a weakening subpolar gyre could still drastically affect the climate.

Research has indicated that the AMOC might soon face a collapse due to its primary engine faltering. This engine, driven by the descent of dense, cold, and salty water, is being compromised by warming and dilution from meltwater. A similar challenge confronts the subpolar gyre, which relies on surface water descending to the ocean floor, though wind also plays a role in its operation, making a total collapse unlikely.

Although a weakening subpolar gyre does not automatically imply an AMOC collapse, its impact on climate, especially during historical periods like the Little Ice Age, is notable. During this time, average temperatures plummeted, wreaking havoc across Europe and North America.

Clues in Clams

In their study, Arellano Nava and her team analyzed data from the shells of North Atlantic clams, Arctica islandica and Glycymeris glycymeris. These shells, akin to tree rings, provide historical oceanic data. “With clam records, we have that nice dating for each of the layers,” Arellano Nava noted.

The research compiled 25 datasets, painting a 150-year history of the North Atlantic subpolar gyre. Two distinct periods of instability were identified, one of which aligns with the 1920s North Atlantic regime shift. This historical instability suggests that the subpolar gyre might have been recovering from its Little Ice Age state.

Despite the robust data, some experts remain skeptical. David Thornalley from University College London appreciates the value of these datasets but questions the strong link between observed patterns and oceanic physical features. “I am skeptical about the interpretation,” he stated.

As the study continues, Arellano Nava and her team are exploring potential climate scenarios that could emerge from the gyre’s ongoing destabilization. “We don’t know exactly what the tipping point is, but we may be observing a subpolar gyre weakening first,” she concluded, expressing her concern.