Atlantic Ocean May 'Soon' Begin to Close

The vast stretch of ocean between the Americas and Europe may be about to close soon—on a geological timescale.

Just before the continents begin to drift back together, an "Atlantic ring of fire" is expected to form, with the area of tectonic activity moving from the Mediterranean into the Atlantic, according to a new paper in the journal Geology.

This is due to begin happening in about 20 million years—just around the corner geologically, but an unfathomably long period of time on a human scale.

Tectonic plates are constantly moving, just incredibly slowly. Sometimes, oceans are born as plates move apart and close again as plates move back together over hundreds of millions of years, in a process called the Wilson Cycle. This is what drove the megacontinent of Pangaea to break up 180 million years ago, forming the Atlantic, and squishing the ancient ocean Tethys into what is now the Mediterranean.

For the Atlantic to close, new subduction zones need to form. These are places where one plate is forced beneath the other into the Earth's mantle, occurring due to differences in density between the two plates, typically with an oceanic plate being subducted beneath a continental plate or another oceanic plate.

Subduction zones are characterized by intense geological activity, including earthquakes, volcanic eruptions and the formation of deep oceanic trenches.

These zones are hard to form, however, as plates are very strong and a subduction zone would require a plate to break and bend. However, subduction zones that already exist can migrate in a process known as subduction invasion.

According to the paper, which used computational models to predict future plate tectonics, the subduction zone in the Mediterranean underneath the Gibraltar Strait is expected to move further into the Atlantic in about 20 million years, forming an Atlantic ring of fire like the one surrounding the Pacific.

"Our work suggests that a small subduction zone that is now below the Gibraltar Arc is dormant but will spread inside the Atlantic in the next 20 million years. This subduction zone, together with another two that already exist on the other side of the Atlantic—in the Caribbean and near Antarctica—will contribute to the formation of an Atlantic ring of fire that with time may lead to its closing," paper co-author João Duarte, a researcher at the University of Lisbon's Instituto Dom Luiz, told Newsweek.

The researchers describe how the Gibraltar subduction zone has slowed down over the past few millions of years, with few scientists considering it still active. After the zone enters the Atlantic, however, it is expected to get much more active, driving the closing of the Atlantic Ocean over several more millions of years.

"According to our calculations, the Atlantic may close in around 200 million years, which is more or less the time it took to open," Duarte said.

"The main driver of subduction zones is the weight of the plate that is subducting. When oceanic plates form at mid-ocean ridges, they are hot and buoyant, but as they move away from the ridge, they cool and become heavy. Gravity will do the job and eventually pull them down back into the Earth's mantle. But for plates to start sinking, they need to break and bend. And this is not easy (plates are thick and strong)," Duarte said.

"So it was always a paradox to understand how subduction zones form in opening Atlantic-type oceans, which generally do not have subduction zones. We suggest that these subduction zones migrate from oceans that have subduction zones (like the Pacific and the Mediterranean) into oceans that do not have them. It is almost like an infection. Subduction is transmitted from ocean to ocean."

The researchers concluded that invasive subduction may be a common way that oceans like the Atlantic start to close and, therefore, may be a major factor in how our planet has geologically evolved.

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Update 2/21/24, 2:03 p.m. ET: This article was updated with comment from João Duarte.