Study: Marine Shell Data Tracks Changes In Ocean Currents; Large Changes In Conveyer Possible Under Today's Conditions [View all]

A new study analyzing chemical traces in the growth rings of clam shells reinforces growing concerns about the stability of a key North Atlantic Ocean current that helps keep the global climate livable. The findings, published on Thursday in Science Advances, examined changes in the ocean south of Greenland during the last 150 years and found that the inflow of freshwater has been disrupting the subpolar gyre, which distributes ocean heat, since the 1950s.

The research is another sign that climate heating caused mainly by fossil fuel pollution is pushing the climate toward dangerous tipping points, out of the “safe operating space” for humans, said lead author Beatriz Arellano-Nava, a University of Exeter climate researcher. A weakening or shutdown of the subpolar gyre and related currents would weaken the northward transport of ocean heat from the tropics to higher latitudes, with different impacts by region. The tropics would experience more extreme heat on land and even worse ocean heatwaves than those already killing billions of marine organisms, from sea stars to sea birds. Sea level rise in most of the tropics would also accelerate from thermal expansion, with warming oceans swelling higher onto shorelines.

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Varying oxygen isotopes show changes in seawater linked to temperature and the influence of different water masses, which helps show the changes in ocean circulation, she said. The width of the growth rings tells scientists about temperature, the supply of food to the seabed and circulation dynamics that bring nutrients, she added. The changes in the rings are clear once a tipping point has been crossed, she said, explaining that during a transition to a colder climate period in the Northern Hemisphere a few hundred years ago, the shift of oxygen isotope values reflected colder conditions and a stronger influence of Arctic waters. And the growth bands became narrower, indicating both lower temperatures and reduced food availability.

Levermann, the Potsdam Institute researcher, said the new paper is remarkable because it provides direct evidence that vital ocean circulations can shift into a new state under current oceanic and atmospheric conditions, not just in a theoretical model or under vastly different ancient climate conditions. “To find such recent evidence for tipping in a large oceanic system is worrisome and supports the increasingly large literature on tipping points from Antarctica to Greenland and the Amazon rain forest,” he said.

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https://insideclimatenews.org/news/03102025/atlantic-meridional-overturning-current-disruption/