Major Indian Ocean current widens as climate warms

The Indian Ocean’s Agulhas Current is getting wider rather than strengthening, according to a new study which may have important implications for global climate change.

The findings suggest that intensifying winds in the region may be increasing the turbulence of the current, rather than increasing its flow rate, researchers said.

Using measurements collected during three scientific cruises to the Agulhas Current, the Indian Ocean’s version of the Gulf Stream, researchers at University of Miami in the US estimated the long-term transport of the current leveraging 22 years of satellite data.

They found the Agulhas Current has broadened, not strengthened, since the early 1990s, due to more turbulence from increased eddying and meandering.

One of the strongest currents in the world, the Agulhas Current flows along the east coast of South Africa, transporting warm, salty water away from the tropics towards the poles.

The Agulhas, which is hundreds of kilometres long and over 2,000-metre0s deep, transports large amounts of ocean heat and is considered to have an influence not only on the regional climate of Africa, but on global climate as part of the ocean’s global overturning circulation.

“Changes in western boundary currents could exacerbate or mitigate future climate change,” said Lisa Beal, professor at UM Rosenstiel School.

“Currently, western boundary current regions are warming at three times the rate of the rest of the world ocean and our research suggests this may be related to a broadening of these current systems,” said Beal.

Previous studies have suggested that accelerated warming rates observed over western boundary current regions, together with ongoing strengthening and expansion of the global wind systems predicted by climate models relate to an intensification and pole-ward shift of western boundary currents as a result of human-made climate change.

“To find decades of broadening, profoundly impacts our understanding of the Agulhas Current and its future role in climate change,” said co-author Shane Elipot, an associate scientist. “Increased eddying and meandering could act to decrease poleward heat transport, while increasing coastal upwelling and the exchange of pollutants,” said Elipot.