Greenland Meltwater Could be Messing With Global Ocean Circulation, Scientists Find

greenland meltwater ocean current study climate change
A new study found that the melting Greenland ice sheet might affect a key aspect of global ocean circulation, which in turn could drive changes in Earth's climate. NASA/Reuters

Take a minute to familiarize yourself with the Atlantic Meridional Overturning Circulation (AMOC). It's a massive ocean current system that's critical to the stability of our climate, as it moves a significant amount of heat from the Southern Hemisphere and the tropics up toward the North Atlantic, where that heat is released to the atmosphere.

For Europe and North America, the AMOC helps regulate how seasons are experienced. But in a study published Friday in the journal Nature Communications, scientists at the University of South Florida used NASA data to conclude that Greenland's rapidly melting ice sheet could be slowing down the AMOC. And that could be a problem.

A map of the surface currents (solid curves) and deep currents (dashed curves) that form a portion of the Atlantic meridional overturning circulation (AMOC). USGCRP/R. Curry/Woods Hole Oceanographic Institution

As the Greenland ice sheet melts and the meltwater runs off (and it's running off much faster than previously thought, according to the latest research), more and more cold freshwater is pushed into the Labrador Sea. The scientists used data from NASA's gravity-sensing GRACE satellite mission to determine that that freshwater is significantly "freshening" the North Atlantic Ocean. Freshwater is more buoyant than salt water, and the GRACE mission can detect that subtle difference in height—and therefore gravitational pull—of the more-buoyant water.

The Greenland runoff, then, "has the potential to increase the buoyancy of surface waters and reduce formation of dense, deep water that helps drive the overturning circulation," explained Don Chambers, a professor of marine science at USF College and an author on the study, in a statement. That, in turn, could "weaken," or slow down, the AMOC. In other words, this ocean current could be knocked off-kilter.

"The major effect of a slowing AMOC is expected to be cooler winters and summers around the North Atlantic, and small regional increases in sea level on the North American coast," Chambers said.

On a global scale, however, the effects are much harder to understand—but could be more consequential.

"The AMOC and Gulf Stream are part of a complex global ocean circulation system that is still not completely understood," Tom Dixon, another USF professor and author on the study, said. "If human activities are starting to impact this system, it is a worrying sign that the scale of human impacts on the climate system may be reaching a critical point."