Slowdown of Major Ocean Currents in the Atlantic: Key Insights and Implications

The latest buoy measurements indicate that the Atlantic Meridional Overturning Circulation (AMOC), crucial for regulating Europe’s climate, is weakening across four distinct latitudes. This represents the strongest evidence yet that this pivotal ocean current system is slowing and may be nearing collapse.

The AMOC is part of a global oceanic conveyor belt that transports warm, salty water from the Gulf of Mexico to the North Atlantic, helping maintain milder temperatures in Western Europe compared to those in Canada or Russia. As this water cools and sinks, it continues south along the ocean floor on the western side of the Atlantic.

Analysis of historical ocean temperature data suggests a 15% decline in the AMOC since 1950, with computer models predicting a potential closure within decades. However, direct measurements have only been reliable for roughly 20 years, making definitive conclusions difficult.

Recent research in the Western Atlantic has provided compelling evidence of an AMOC slowdown.

“Our findings indicate that Atlantic circulation is indeed weakening at the western boundary, and data from multiple latitudes supports this consistent signal across the broader North Atlantic,” said Qianjiang Xing from the University of Miami, Florida, who led the study.

In 2004, a collaborative effort led by the University of Miami established a series of moorings named RAPID-MOCHA from the Bahamas to the Canary Islands. These measurements, encompassing temperature, salinity, and velocity, allow scientists to estimate pressure changes across the Atlantic, providing insight into how much water is being effectively stored, according to team member Shane Elipot, also from the University of Miami.

Water moves from areas of high pressure to those of low pressure, but the Earth’s counterclockwise rotation causes deflection to the right, leading to reverse circulation. Thus, pressure changes can be indicative of AMOC strength variations.

The latest analysis of RAPID-MOCHA data reveals that AMOC flow is decreasing at a rate of approximately 90,000 cubic meters per second each year—a faster decline than previously observed. This indicates that the AMOC weakened by about 10% from 2004 to 2023.

However, the variation in certainty surrounding this reported change is quite significant. To address this, the study also examined pressure dynamics from three mooring arrays installed along the western Atlantic coast—near the West Indies, the U.S. East Coast, and Nova Scotia, Canada. Results show considerably lower uncertainty and a more pronounced weakening of the AMOC.

“This represents the strongest direct observational evidence to date of AMOC weakening, aligning with long-held model predictions,” commented Stefan Rahmstorf from the University of Potsdam in Germany, who was not involved in the study.

Scientists speculate that freshwater from the melting Greenland ice sheet is diluting the AMOC’s intensely salted waters, impeding their sinking action and thus weakening the southward flow along the ocean floor of the western Atlantic. The observed declining trends across four latitudes in the Western Atlantic point to this phenomenon.

“We anticipate these changes to be evident deep within the western boundary,” team members assert, including David Smeed from the UK National Marine Centre. “This strengthens our confidence in that interpretation.”

“They provide the first robust evidence of a consistent weakening of overturning across various latitudes in the Deep West,” claims René van Westen, a professor at Utrecht University in the Netherlands, who did not participate in the study.

Elipot emphasized the need for ongoing observations to clarify whether the AMOC is on the brink of collapse, a scenario that could lead to significantly colder winters in Europe and disrupt monsoon patterns in Asia and Africa.

“This trend suggests we might be approaching a tipping point,” he notes.