Atlantic Ocean may be nearing a climate tipping point

The Atlantic Ocean has always been a powerhouse of climate regulation. But new findings reveal that this vast system might be nearing a critical threshold.

A recent study based on clam shells and supported by advanced modeling shows that two key North Atlantic currents are becoming unstable. The results indicate the ocean’s delicate balance could soon reach a point of no return.

Clams reveal ocean history

Scientists from the University of Exeter and collaborators analyzed shells of quahog clams and dog cockles, species that can live for centuries.

Each shell contains yearly layers, storing physical and chemical clues about the ocean’s past. These archives allow researchers to trace changes over hundreds of years without gaps in data.

“Anticipating a tipping point requires good data, covering a long period with no gaps,” explained study lead author Dr. Beatriz Arellano Nava.

How ocean currents work

By reading shell bands, researchers reconstructed a continuous record of Atlantic circulation behavior, focusing on two critical systems: the Atlantic Meridional Overturning Circulation (AMOC) and the Subpolar Gyre (SPG).

Both systems transport heat across the planet. The AMOC carries warm water northward, helping to keep Europe mild. The SPG stabilizes the North Atlantic climate by circulating cooler waters.

If the AMOC collapses, winters in Europe could become harsher, while rainfall patterns might change globally. A weakened SPG could still cause more storms and regional temperature swings.

Atlantic Ocean weakening

The study used 25 shell-based records from the North Atlantic shelves, applying indicators such as autocorrelation and restoring rate to detect stability loss.

When these indicators rise over time, it means the system is taking longer to recover from disturbances – a sign of “critical slowing down,” a known precursor to tipping points.

Across twelve key sites – from Newfoundland to Norway – scientists found two major destabilization periods.

The first occurred before the 1920s regime shift, suggesting an early crossing of a tipping point. The second began around 1950 and continues today, aligning with broader evidence of ocean weakening.

Evidence of change

The study revealed that the strongest instability occurred in areas sensitive to SPG temperature changes. This indicates that basin-scale processes, rather than local weather, drive the destabilization.

“When a system is stable, there will still be variations – but we would typically see a rapid return to the normal state after a change,” said Professor Paul Halloran, co-author of the study.

“When a system destabilizes, it doesn’t recover as quickly – and this could be a sign of an approaching tipping point.”

Atlantic Ocean instability

Bivalve records show a rise in instability before 1920, followed by a decline and then another increase after 1950.

These patterns match ocean temperature data from modern models, confirming that the results are not artifacts of statistical processing but genuine climate signals.

The early 20th century destabilization coincided with a known North Atlantic regime shift that brought warmer conditions and biological changes, including shifts in fish populations.

The later destabilization, still ongoing, reflects the cumulative effects of human-driven climate change.

Lessons from the Atlantic Ocean

Researchers concluded that the SPG and AMOC may both be losing stability, but it is difficult to pinpoint which is closer to a critical state.

Evidence from the Science Advances study suggests the SPG might weaken first. A weaker SPG could alter ocean heat transport, disrupt regional ecosystems, and affect the AMOC’s ability to circulate deep water.

“Melting of polar ice due to climate change is certainly contributing to the weakening of ocean currents and pushing them closer to a tipping point,” said Dr. Arellano Nava.

Rapid ice melt adds freshwater, disrupting density-driven circulation. This imbalance threatens to amplify instability across the entire Atlantic system.

An ocean under pressure

The research combines biology and physics, showing how long-lived marine organisms can record early warning signs of climate imbalance.

These shell records extend the timeline of ocean monitoring far beyond human observation. The findings emphasize that the Atlantic is already showing symptoms of declining resilience.

The study, funded by the European Union’s Horizon 2020 COMFORT and ARIA AdvanTip projects, concludes that the North Atlantic may be entering a dangerous phase.

“Rapidly reducing greenhouse gas emissions is the best way to prevent tipping points in the Atlantic Ocean,” said Dr. Arellano Nava.

The clam shells, once silent witnesses of history, now speak urgently of an ocean under strain. Their layered memories warn us: if humanity does not act, the tides of change could become irreversible.

The study is published in the journal Science Advances.

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