Japanese and Australian researchers have found that a deep-sea current moves millions of cubic metres of water northward from Antarctica every second.
The scientists came to the conclusion after two years of measurements.
Previous studies had noted a deep current along the eastern edge of the Kerguelen Plateau, an over 2,200—kilometre—long rise about 3,000 kilometres southwest of Australia. However, estimates of its speed, taken as “snapshots” by instruments used from research vessels, had been “all over the place”, according to Steve Rintoul, a physical oceanographer at the Antarctic Climate and Ecosystem Cooperative Research Centre in Hobart, Australia, and a co—author of the new study.
Yasushi Fukamachi, an ocean scientist at Hokkaido University in Sapporo, Japan, fronted a team effort to find the exact nature of the current. The scientists moored more than 30 current and temperature recorders across its probable path for two years. After retrieving the instruments they discovered the current, which flows at depths below 3,000 metres, at times hit speeds greater than 700 metres per hour, carrying volumes as high as 30 million cubic metres per second. No other deep current in the Southern Hemisphere moves that quickly.
The current is formed by cold water sinking in the Ross Sea and off the coast of Adelie Land, on the Australian—facing side of Antarctica. Once in the abyss, the water flows eastward along the coast of Antarctica before hitting the Kerguelen Plateau. Then, just as the Gulf Stream hugs the eastern edge of North America, Coriolis force from Earth’s rotation causes the Antarctic water to embrace the plateau’s eastern flank. The result is a narrow, and so fast—moving, stream, about 50 kilometres wide.
This is important because it represents a “fast lane” by which climatic and environmental changes affecting the Southern Ocean can propagate northward, pointed out Alejandro Orsi, a physical oceanographer at Texas A & M University in College Station, who was not involved in the study.
According to him, proof that this is already taking place can be seen from the fact that the deep waters near the Kerguelen Plateau already show “clear signs” of reduced salinity relating to changes in the rate of melting of Antarctic ice sheets. Richard Alley, a geoscientist at Pennsylvania State University in University Park, believes understanding such currents could help scientists to predict how the world will react to increasing levels of carbon dioxide, reports Nature.
He said if heat warms the deep ocean rather than surface waters, it will have less effect on sea—level rise because cold water in the ocean’s depths expands less than warm surface waters.
Similarly, heat and carbon dioxide contained in deep—ocean currents are sequestered from the atmosphere until the water rises back the surface, many years later.
Similar flows in the North Atlantic account for the fact that Europe is warmer than comparable latitudes in Japan, Fukamachi said.
But the currents could change. “We’re not saying this could happen instantaneously, like the movie The Day After Tomorrow,” Fukamachi said, “but understanding this kind of current is very important to understanding global climate.”
