A narrow, high-speed, westward flow which extends for more than 1000 km along the coast of Alaska. This is a separate feature from the offshore, deepwater Alaskan Stream. It was not recognized as such up until the mid-1970s when a series of hydrocast surveys in the area was begun which led to its identification as a distinct circulation feature. The ACC is driven by freshwater discharge from the mountainous and coastal regions around the Gulf of Alaska and the consequent nearshore confinement of this low-salinity water by westward winds. It is typically narrow (<50 km), shallow (<150 m) and partially baroclinic. It flows most intensely between 145 and 155° W through the Shelikov Strait between the Alaskan Peninsula and Kodiak and Afognak Islands, but extends recognizably along the Peninsula as far as 165° W.

The baroclinic speeds and transports have been estimated as typically <30 cm s^-1 and 0. 4 Sv, respectively, in the winter, spring and summer. In the fall, when the freshwater influx leads to the spin-up of the ACC, the speeds and transports have been estimated as 89-133 cm s^-1 and 1. 0-1. 2 Sv, respectively. Current mooring measurements have yielded estimates of six-month mean total transports ranging from 0. 85 Sv at 151° W to 0. 64 Sv at 155° in Shelikof Strait, with daily means as high as 2. 5 Sv and marked variability from day to day. This variability is thought to be mainly due to variations in wind-forcing caused by the passage of large-scale storms along the coast. The mean baroclinic transport as estimated from the same measurements was found to be about 75% of the total.