Using underwater robots in waters surrounding Antarctica, scientists have shown that the intersection of strong currents with the slope of landmasses rising from the ocean floor makes a significant contribution to the mixing of different waters in the Southern Ocean.
The finding, detailed in a paper recently published online in the journal Nature Geoscience, has bearing on models of heat transport toward Antarctica and the ocean's role in the carbon cycle. According to the study, in the ocean, global water properties may depend on very localized mixing processes.
"Most global ocean observations acquire measurements in the open ocean or in the top layers of the water, while our research shows that important mixing processes may be occurring in the deep ocean in thin layers over sloping topography," senior author Andrew Thompson, professor at California Institute of Technology (Caltech), was quoted as saying in a news release on Friday.
The research team from Caltech deployed two autonomous underwater drones, or "gliders," for a period of eight months over the course of a year and a half in the Southern Ocean, which encircles Antarctica.
They concentrated on the region around Drake Passage, the 1,000-kilometer-wide waterway between Antarctica and South America.
The gliders were able to reach depths of 1,000 meters, nearly scraping the bottom at times. When they come to the surface, they regularly relay this data back to Thompson and his colleagues.
The data were collected by the instruments, which the gliders carry to measure temperature, salinity, the quantity of various nutrients like nitrogen and iron, and other variables.
"There is growing evidence that topography plays a bigger role in oceanographic mixing than we had previously suspected," says lead author Xiaozhou Ruan, a Caltech graduate student. "While this boundary region represents a small fraction of the ocean, the interaction between water and continental topography plays an outsized role in mixing."
Such mixing has been predicted by high-resolution ocean circulation models, but this is the first time it has been observed directly over a period of many months, according to Caltech.
Documenting these physical processes and improving our understanding of where and how they arise may improve our ability to simulate the changes in ocean circulation and in Earth's climate in the past and in the future, researchers say.