Deep western boundary current and southern frontal systems of the Antarctic Circumpolar Current southeast of the Kerguelen Plateau

Abstract

The structures of the deep western boundary current and southern frontal systems of the Antarctic Circumpolar Current (ACC) southeast of the Kerguelen Plateau were investigated. Top‐to‐bottom hydrography was conducted around 58°S, and two underway observations were made around 56°S and 61°S. Middepth floats were also used to describe the subsurface flow and temperature fields. Along the 58°S section, a cold dome was located just off the plateau, and northwestward and southeastward flows were found in its western and eastern sides. The observed flow structure was highly barotropic. The maximum volume transport of the bottom water was 22 Sv equatorward, including a possible cyclonic recirculation of 10 Sv. The transport of the deep recirculation can be explained by the potential vorticity homogenization in the closed isopachs formed by the bottom slope off the plateau and the overlying ACC flowing southeastward through the Fawn Trough. The spatial scale of the cold dome, which showed a signature of the southern ACC front, was around 100 km at 58°S, and the similar cold domes were also found around 56°S and 61°S, along with a signature of the southern boundary of ACC around 61°S. The sharp excursion of the southern ACC front was also confirmed by the middepth float trajectories and the distribution of temperature maximum. This indicates the equatorward excursion up to 54°S, with the warmer ACC water just east of the southern frontal systems.