In a new study which has important implications for global climate change, researchers from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science have found that the Indian Ocean’s Agulhas Current is not strengthening, but getting wider. This suggest that the winds that have been intensifying in the region may not be increasing the flow rate of the current, but rather its turbulence.
Researchers have leveraged 22 years of satellite data and used measurements collected during three scientific cruises to the Agulhas Current. The data was then used to estimate the long-term transport of the current. They found that due to more turbulence from increased meandering and eddying, the Agulhas Current has not strengthened, but broadened since the early 1990s.
The Agulhas Current, the Indian Ocean’s version of the Gulf Stream, is one of the strongest currents in the world and flows along the east coast of South Africa. It transports salty, warm water away from the tropics toward the poles. The Agulhas is over 2,000-meters deep and hundreds of kilometers long. It transports large amounts of ocean heat and is thought to influence not only the regional climate of Africa, but also the global climate as part of the ocean’s global overturning circulation.
Lisa Beal, a UM Rosenstiel School professor of ocean sciences and lead author of the study, notes that future climate change can be mitigated or exacerbated by changes in western boundary currents. Western boundary current regions presently warm at three times the rate of the rest of the world ocean. The new research suggests this may be related to a broadening of current systems such as the Agulhas Current.
Studies done previously have suggested that the faster warming rates that have been observed over western boundary current regions, combined with ongoing expansion and strengthening of the global wind systems predicted by climate models, relate to an intensified shift of western boundary currents towards the poles as a result of human made climate change.
Shane Elipot, a UM Rosenstiel School associate scientist and study co-author, notes that the discovery of decades of broadening, rather than intensification, has profoundly impacted on our understanding of the Agulhas Current and its future role in climate change.
Poleward heat transport could be decreased by the increased meandering and eddying, while coastal upwelling and the exchange of larvae and pollutants across the current from the coast to the open ocean could increase.