For two years, UM’s Lisa Beal and collaborators gathered hourly measurements of velocity, temperature, and salinity in the Agulhas Current along the southeast coast of Africa. Their data show that while frontal eddies and meanders are pumping deep, cold, nutrient-rich water onto the shelf, offshore meanders are trapping heat and salt closer to the surface.

This helps explain the rapid warming of the current’s surface at the same time that its heat transfer to higher latitudes has apparently declined. “More eddy activity is accelerating surface warming in the Agulhas, while simultaneously enhancing hidden upwelling that cools deeper waters,” says Beal. “This combination—along with the onshore encroachment also driven by eddies—will create more extreme conditions in shelf seas in the future, potentially placing significant strain on coastal ecosystems.”

• Lisa Beal