In a new study from the University of Exeter, researchers have identified the key factors that influence the Atlantic meridional overturning circulation (AMOC). This critical ocean current pattern carries warm water from the tropics northward.
“The Atlantic meridional overturning circulation (AMOC) is pivotal for regional and global climate due to its key role in the uptake and redistribution of heat and carbon,” wrote the study authors.
“Establishing the causes of historical variability in AMOC strength on different timescales can tell us how the circulation may respond to natural and anthropogenic changes at the ocean surface.”
Many scientists believe that heat transport through the AMOC is responsible for making some regions, including northwest Europe and the UK, warmer than they would be otherwise. Climate model simulations suggest that the AMOC could weaken in the coming decades, with widespread implications for regional and global climate.
In collaboration with experts at the University of Oxford, the Exeter team has managed to pinpoint the causes of monthly and annual AMOC variation.
The study was focused on observational data from large arrays of monitoring equipment off the coasts of Florida and Africa, and in the North Atlantic between Greenland and Scotland.
“Understanding AMOC variability is challenging because the circulation is influenced by multiple factors that all vary and whose overlapping impacts persist for years,” explained study lead author Dr. Yavor Kostov. “Our findings reveal the vital role of winds in driving changes in this ocean circulation.”
“Winds were a key factor both in the sub-tropical and sub-polar locations we examined. As the climate continues to change, more efforts should be concentrated on monitoring those winds – especially in key regions on continental boundaries and the eastern coast of Greenland – and understanding what drives changes in them.”
While AMOC variability off the southern United States was found to be dominated by wind variability, the combined effects of wind, heat, and freshwater anomalies were found to influence variability in the North Atlantic.
“Our reconstruction suggests that, compared to the subtropics, the overturning circulation in the subpolar North Atlantic is more sensitive to changes in the background ocean state such as shifts in the sites of deep convection,” said Dr. Kostov.
“This implies that future climate change may alter annual AMOC variability in this region. It emphasises the need for continued observations of the subpolar North Atlantic ocean.”
The researchers also discovered that changes in the surface temperature and salinity near Canada and Greenland can trigger a delayed remote impact on the Atlantic circulation as far south as Florida.
The study is published in the journal Nature Geoscience.