New Observations Call AMOC-Climate Disaster Fears Into Question

New findings from an international ocean observing network are calling into question the longstanding idea that global warming might slow down a big chunk of the ocean’s “conveyor belt.”

The first 21 months of data from sensors moored across much of the North Atlantic are giving new insight into what controls the strength of the Atlantic Meridional Overturning Circulation, a system of currents that redistributes heat around much of the Western Hemisphere.

Researchers had thought the strength of that circulation, known by the acronym AMOC, was largely influenced by the sinking of cold, fresh water in the Labrador Sea, between Greenland and Canada. And climate simulations suggest that the sea’s deepwater formation might slow as the world continues to warm — which also could slow down the entire Atlantic current system and possibly make temperatures on land in the northeastern United States and the United Kingdom plunge. That concept inspired the (otherwise unrealistic) 2004 climate apocalypse film The Day After Tomorrow.

But, the data collected over those 21 months show that the Labrador Sea’s influence on the AMOC paled in comparison with that of another North Atlantic ocean region, just east of Greenland. How the intensity of deepwater formation in that area changed with time accounted for 88 percent of the observed variability in the entire AMOC, physical oceanographer Susan Lozier of Duke University and colleagues report in the Feb. 1 Science.

The results provide “an unprecedented insight into how the modern North Atlantic operates,” says paleoceaonographer David Thornalley of University College London, who was not involved in the study.

Atlantic Ocean circulation is driven by differences in water density related to freshness and temperature: Warm, salty water (including the Gulf Stream) flows north at the ocean surface, delivering heat to the northeastern United States and the British Isles. Near Greenland, the current splits, with one arm heading for the Labrador Sea west of Greenland and the other toward the Nordic Sea to the east. There, the waters become both colder and fresher, thanks to meltwater from land. The colder water then sinks and travels south again along the ocean floor.

Many studies have suggested that the Labrador Sea regulates AMOC’s strength, but those are largely based on climate simulations, Lozier says. “We need to ground-truth the simulations,” she says. “This is where we really need observations.”