Scientists say it vital to understand the Antarctic Circumpolar Current’s dynamics
A satellite image shows a major ocean current that is speeding up due to climate change.
The Antarctic Circumpolar Current (ACC), which sweeps around the abyss off Antarctica, is the only ocean current that circumnavigates the planet.
Researchers used satellite measurements of sea-surface height and data collected by the global network of ocean floats called Argo to detect a trend in Southern Ocean upper layer velocity that had been hidden to scientists until now.
The researchers found that prevailing westerly winds have sped up as the climate warms. Models show that the wind speedup does not change the ocean currents much. Rather, it energises ocean eddies, which are circular movements of water running counter to main currents.
“From both observations and models, we find that the ocean heat change is causing the significant ocean current acceleration detected during recent decades,” said Jia-Rui Shi, formerly a PhD student at Scripps Oceanography and currently a postdoctoral researcher at Woods Hole Oceanographic Institution.
“This speedup of the ACC, especially its jet centred on the Subantarctic Front, facilitates property exchange, such as of heat or carbon, between ocean basins and creates the opportunity for these properties to increase in subsurface subtropical regions.”
The ACC encircles Antarctica and separates cold water in the south from warmer subtropical water just to its north. This warmer part of the Southern Ocean takes up a lot of the heat that human activities are adding to Earth’s atmosphere.
For this reason, scientists consider it vital to understand its dynamics, since what happens there could influence climate everywhere else.
The ocean warming pattern is important. When the gradient, or amount of heat difference, between warm and cold waters increases, currents between those two masses speed up.
“The ACC is mostly driven by wind, but we show that changes in its speed are surprisingly mostly due to changes in the heat gradient,” said co-author Lynne Talley, a physical oceanographer at Scripps Oceanography.
Besides Shi and Talley, the research team included Scripps Oceanography climate scientist Shang-Ping Xie, Qihua Peng of the Chinese Academy of Sciences, and Wei Liu of UC Riverside.