Atlantic Ocean Current Has Been Weakening for Nearly 20 Years

Key Points

• Scientists found evidence that the Atlantic Meridional Overturning Circulation has been weakening for nearly two decades.
• The decline was detected across a broad stretch of the North Atlantic, from about 16.5°N to 42.5°N.
• The AMOC helps move heat through the Atlantic and influences temperatures, rainfall, storms and sea levels.
• Researchers used long-term measurements from four ocean monitoring systems along the western North Atlantic.
• Scientists say continued monitoring could help provide an early warning of wider climate changes.

Scientists have found some of the clearest observational evidence yet that a major Atlantic Ocean circulation system has been weakening for nearly 20 years. The system, known as the Atlantic Meridional Overturning Circulation, or AMOC, plays an important role in moving heat through the Atlantic and influencing climate conditions around the region.

The new research was led by scientists at the University of Miami Rosenstiel School of Marine, Atmospheric and Earth Science. Their findings suggest the weakening is not limited to a small part of the ocean, but can be seen across a broad section of the western North Atlantic. That matters because changes in a large-scale circulation system can eventually affect weather and sea levels well beyond the area where the measurements are taken.

The AMOC works as a huge ocean conveyor system. Warm water moves northward near the surface, while colder and denser water travels southward at greater depths. This movement redistributes enormous amounts of heat through the Atlantic, helping shape temperatures, rainfall and other climate conditions in parts of Europe and North America.

To understand how the circulation has changed, researchers examined long-term observations from four monitoring arrays positioned along the western side of the North Atlantic. The sites stretch from tropical waters into higher latitudes, giving the scientists measurements from different parts of the basin rather than relying on a single location.

The monitoring systems use instruments anchored to the seafloor to record pressure, temperature, density and ocean currents. The researchers paid particular attention to changes in pressure at the ocean bottom, using those measurements to estimate the movement of deep water below roughly 1,000 meters.

The results showed a similar decline at several different latitudes, covering an area between about 16.5°N and 42.5°N. According to the researchers, seeing the same broad pattern across multiple locations makes it more consistent with a larger change in Atlantic circulation than with a short-lived local fluctuation.

The potential effects are significant because the AMOC is closely connected to the distribution of heat in the North Atlantic. A continued weakening could influence European winters, rainfall patterns, storm activity and coastal sea levels, although the research itself focuses on the observed circulation decline rather than predicting a specific future outcome.

Researchers also say the western boundary of the Atlantic could become an important place to monitor future changes. Long-term measurements in this region may help scientists identify broader shifts in the AMOC before their effects become more apparent in other parts of the climate system.

Shane Elipot, a senior author of the study and physical oceanographer at the Rosenstiel School, said a weaker AMOC can shift weather patterns and potentially contribute to changes in storms, rainfall and winter conditions. He also noted that changes in the circulation can influence sea-level rise along coastlines.

The researchers stressed the importance of maintaining long-term ocean observations. Ocean currents naturally vary over years and decades, so extended records allow scientists to separate temporary changes from longer-lasting trends.

The study, titled “Meridionally consistent decline in the observed western boundary contribution to the Atlantic Meridional Overturning Circulation,” was published in Science Advances. The research was supported by grants from the U.S. National Science Foundation and the UK Natural Environment Research Council.