A major system of ocean currents in the Atlantic has been losing strength for close to 20 years, and scientists say the decline is broad enough to suggest a large-scale shift in how the ocean is moving, not a temporary fluctuation.
The research comes from scientists at the University of Miami Rosenstiel School of Marine, Atmospheric and Earth Science. According to Science Daily, their findings represent some of the strongest direct observational evidence gathered so far that the Atlantic Meridional Overturning Circulation, known as the AMOC, is weakening.
The AMOC is a vast system of currents that moves warm water from the tropics northward along the surface of the Atlantic and returns colder, denser water southward along the ocean floor. It functions somewhat like a conveyor belt, and it plays a central role in regulating temperatures and weather across large parts of Europe and North America.
To track changes in the system, the research team examined long-term data from four ocean monitoring arrays spread along the western side of the North Atlantic. The sites ranged from tropical waters near 16.5 degrees north latitude up to mid-latitudes around 42.5 degrees north. Instruments anchored to the seafloor continuously recorded pressure, temperature, density, and current movement at depths below roughly 1,000 meters.
By applying the same analytical method across all four sites and comparing measurements taken over time, the scientists identified a consistent and sustained decline in the deep ocean circulation along the western boundary of the Atlantic.
The geographic range of the slowdown was one of the findings that stood out. Because the weakening appeared across such a wide stretch of the Atlantic, not just at one location, the researchers concluded it reflects a genuine long-term change rather than a regional or short-lived variation.
"A weaker AMOC can shift weather patterns, potentially leading to more extreme storms, changes in rainfall, or colder winters in some regions," said Shane Elipot, a senior author of the study and physical oceanographer at the Rosenstiel School. "It can also influence sea-level rise along coastlines, affecting communities and infrastructure."
Sea level rise tied to AMOC changes would not be uniform. A weaker current system can cause water to pile up along certain coastlines, particularly in the northeastern United States, increasing the risk of flooding in those areas beyond what global average sea level rise would otherwise produce.
Scientists have been concerned about the AMOC's stability for years, but direct observational data confirming a long-term weakening across such a broad region has been limited. Climate models have long projected that the AMOC could slow as global temperatures rise and freshwater from melting ice sheets enters the North Atlantic, disrupting the density differences that drive the circulation. This study adds measured, on-the-ground evidence to support those projections.
The researchers said their findings could help improve the climate models used to project future conditions, giving scientists a better foundation for understanding how ongoing changes in the ocean might reshape weather and sea levels in the decades ahead. The study's methods, which rely on bottom pressure measurements to estimate deep ocean movement, may also offer a more consistent and comparable approach for future monitoring efforts across different parts of the Atlantic.
