A special high-speed winch that the researchers used to swiftly raise and lower instruments to track the dye’s movements underwater. Credit: San Nguyenhave led an international team to directly measure the upwelling of cold, deep water through turbulent mixing along the slope of a submarine canyon in the Atlantic Ocean.
Despite the conveyor belt’s importance, however, a component of it known as meridional overturning circulation , has proven difficult to observe. In particular, the return of cold water from the deep ocean to the surface through upwelling has been theorized and inferred but never directly measured.In 1966, Munk calculated a global average pace of upwelling using the rate at which cold, deep water was formed near Antarctica. He estimated the speed of upwelling at one centimeter per day.
Wynne-Cattanach, Alford, and their collaborators set out to see if they could directly observe this phenomenon by conducting an experiment at sea with the help of a barrel of a non-toxic, fluorescent green dye called fluorescein. Beginning in 2021, the researchers visited a roughly 2,000-meter-deep undersea canyon in the Rockall Trough, about 370 kilometers northwest of Ireland.
Where Munk inferred a global average of one centimeter per day, measurements at Rockall Trough found upwelling proceeding at 100 meters per day. Additionally, the team observed some dye migrating away from the canyon’s slope and toward its interior, suggesting the physics of the turbulent upwelling were more complex than Ferrari originally theorized.