Antarctic Circumpolar Current

The Antarctic Circumpolar Current (ACC), also known as the West Wind Drift, is the only current that flows completely around the globe, unimpeded by continents. Famous explorers have often referenced the ACC in their navigational logs, including Edmond Halley (the first to note the ACC in a voyage from 1699 to 1700), James Cook, James Clark Ross, Sir Francis Drake, and James Weddell. The ACC is notably the roughest sea crossing for navigators, particularly the 497 mi. (800 km) wide Drake Passage extending around Cape Horn and the Antarctic Peninsula. The role of the ACC as “mixer of the deep oceans” also has a significant impact on global climate.

The ACC, as the name implies, flows around the continent of Antarctica in an eastward direction driven by westerly winds through the Atlantic, Indian, and Pacific oceans. The ACC is as deep as 6,562–13,123 ft. (2,000–4,000 m) and as wide as 1,243 mi. (2,000 km), accounting for the vast transport of waters, despite its relatively slow eastward current. It is estimated that some of the seawater of the ACC travels the entire circumference of the globe (24,900 mi.) in a mere eight years. For comparison, the ACC carries 150 times more water around Antarctica than flows through all of the world’s rivers combined.

While flow of the ACC is not blocked by any landmasses, it is severely constrained by them. The borders of the ACC are further defined by convergence fronts with significant temperature and salinity variability. The greatest temperature change is north of the ACC in the Subtropical Convergence (Front), where the average sea surface temperature decreases from 54 degrees F (12 degrees C) to 45–46 degrees F (7–8 degrees C) in the ACC and salinity decreases from 34.9 or greater to 34.6 or less.

The southern boundary of the ACC is defined by the westward flowing Antarctic Coastal Current with a surface temperature around 30 degrees F (minus 1 degree C). Mean ACC temperature ranges from 41 to 30 degrees F (5 to minus 1 degree C). Climate change and ocean warming will likely have a significant effect on the ACC, because of this typically narrow temperature range. Any otherwise small increases in sea surface temperatures may induce dramatic effects on the system.