Observations of the Antarctic Circumpolar Current and deep boundary current in the southwest Atlantic

Abstract

Fourteen‐month velocity and temperature records from an array of 14 moorings north and west of the Falkland Plateau and supporting hydrographic and tracer data reveal a narrow boundary current that carries dense Antarctic waters. The current flows west along the northern flank of the Falkland Plateau with mean speeds of more than 10 cm s−1 at 5000 m and more than 30 cm s−1 at 2500 m. The westward flow extends from the bottom to at least 1000 m, but the upper portion of the current is a branch of the Antarctic Circumpolar Current (ACC) following the only deepwater route between the Scotia Sea and the Argentine Basin. Waters colder than 0.2°C are too cold to be associated with the ACC at Drake Passage and must ultimately derive from the Weddell Sea as part of the deep thermohaline circulation. The westward transport of water colder than 0.2°C is 8.2 × 106 m3 s−1. In the mean the bottom boundary current is similar to that predicted by the Stommel‐Arons model, but considerable variability is introduced by the meandering of the overlying ACC. Chlorofluorocarbon data suggest that new Antarctic water from the Georgia Basin enters the Argentine Basin via the deep boundary current, which passes beneath the ACC; some new water is also advected east after being entrained in the ACC. Most of the water in the deep boundary current is recirculated water that has been in residence in the Argentine Basin for some time. Water colder than −0.2°C is relatively new to the basin and comprises about 2.5 × 106 m3 s−1 of the westward flow of the boundary current.