In our previous post we wrote that we’d enter the Agulhas Current, a western boundary current, about 4 hours out of Durban. Here are some interesting facts about western boundary currents, and the Agulhas in particular:

They originate from equatorial waters flowing westward in response to easterly winds. Where westerly equatorial flow meets a continental shelf, the equatorial current turns and becomes a western boundary current, earning its name. In the Northern Hemisphere, they veer right, flowing north; in the Southern Hemisphere, they veer left, flowing south.

Along the western edges of ocean basins, they move warm water from equatorial latitudes toward the poles. Their warm-water transport mitigates, to some extent, the incoming solar energy difference between equator and poles; the difference between polar and equatorial regions would be more extreme without them or if they weakened.

Western boundary currents are among the world’s most powerful surface currents, each transporting a warm-water volume in the hundreds to thousands of times that of the Mississippi River. They are major features of the ocean’s surface, and current science indicates they exert an appreciable influence on world climate, especially at high latitudes where solar energy input is significantly less.

Though biology is not our topic here, you might like to know western boundary currents transport not just warm water but entrained populations of warm-water flora and fauna, as well, toward both poles. These populations can leave their signature on the ocean floor below their parent current.

Among western boundary currents, the Indian Ocean’s Agulhas is 2nd only to the Gulf Stream in strength.

Beginning in the equatorial reaches of the Indian Ocean north of Madagascar, the Agulhas Current moves Southern Hemisphere warm water, some originating in the Indonesian equatorial Pacific, poleward along the east coast of Africa. It’s one of the Southern Hemisphere’s counterparts to our Gulf Stream, which we know moves warm equatorial Atlantic water northward along the U.S. eastern seaboard.

Our research vessel, RV Roger Revelle, will be cruising this current during the first week out of port. More on surface currents and their characteristics soon. Hope you’ve enjoyed this post. Till next time...