Submitted Feb 17:

Among western boundary currents, the Agulhas flowing south along East Africa is 2nd only to the Gulf Stream in strength. It carries hundreds to thousands of times the water volume of the Mississippi River. Opposing waves generated by storms off Antarctica can be anomalously large. In meeting the thrust of the Agulhas Current, anomalies can be magnified to produce “rogue” waves of enormous proportions.

Any given western boundary current’s volume is appreciably exceeded by that of the Antarctic Circumpolar Current (ACC), also called the West Wind Drift (WWD). It circles Antarctica west to east and dominates the Southern, or Antarctic, Ocean.The ACC is the granddaddy of surface currents and the only major surface current having the geographic opportunity to circle the earth uninterrupted by land. It flows eastward unbroken in a continual circuit of Antarctica in response to powerful prevailing westerly winds. This unique situation gives the Southern Ocean the capacity to generate exceptionally large waves. Its ferocity and general latitude has earned this part of the world ocean several well-known nicknames, including the “Roaring Forties,” the “Furious Fifties,” and the “Screaming Sixties.” At the ACC’s confluence with the Agulhas, challenging conditions for ships are business as usual.

David and Goliath: Agulhas meets ACC:
The ACC’s powerful action seals the fate of the southwest-bound Agulhas. As the Agulhas leaves the southern tip of Africa, its waters are entrained by the more powerful eastward flowing ACC or West Wind Drift. At this merger, the ACC slams the Agulhas backward upon itself, redirecting it abruptly from southwest to east, and the Agulhas ceases to exist as a discrete current. It can be traced as a hairpin turn on surface current maps and quickly disappears. Oceanographers call this the Agulhas Retroflection.

Such a witches-brew of oceanic forces hammering each other from south, west, and northeast, often all at once, poses serious challenges for vessels operating in these waters — especially scientific vessels, which have to stop for researchers to drop things into the ocean, frequently big, fragile things, and haul them back out, hopefully still functional and intact. Maneuvering an idling vessel is much harder to do than steering it through the waves; maneuvering it in a confused sea appears impossible.

The real challenges... and our appreciation:
So here we are, after a week in the Agulhas Current, now having left it behind for the push of the ACC, some of us still trying to get used to the ocean’s motion making us queasy while struggling to do sensitive work on a pitching deck for the first time in our lives. Suddenly, then, we realize the true challenges are those facing Captain David Murline and 22 crew who run our vessel and keep it comfortable for us. Not only do they make it all happen for us, but they make much of it look easy when we know it’s really not — thanks, guys!

As stated in our Feb. 5th blog post, RV Roger Revelle is operated by the Scripps Institute of Oceanography. The ship is actually owned by the U.S. Navy. Revelle himself was a scientist very interested early on in the problem of CO2 emissions and global warming, so our cruise and the CLIVAR program is appropriately supported. Captain Murline’s enthusiasm for supporting science safely at sea is a great bonus. Thanks, Captain Murline and Scripps Institution of Oceanography. You are great hosts!