Circumpolar structure and distribution of the Antarctic Circumpolar Current fronts: 1. Mean circumpolar paths

High resolution hydrographic sections and maps of the gradient of sea surface height (SSH) reveal that the Antarctic Circumpolar Current (ACC) consists of multiple jets or frontal filaments. Here we use a 15 year time series of SSH observations to determine the circumpolar structure and distribution of the ACC fronts. The jets are consistently aligned with particular streamlines along the entire circumpolar path, confirming and extending the results of an earlier study restricted to the region south of Australia. The intensity of the fronts (as measured by the cross-front gradient of SSH) varies along the fronts and the individual branches merge and diverge, often in response to interactions with bathymetry. Maps of absolute velocity at 1000 m depth derived from Argo trajectories confirm the existence of multiple current cores throughout the Southern Ocean. High resolution hydrographic sections and profiles of temperature and salinity from Argo floats are used to show that the front locations derived from fitting SSH contours to maps of SSH gradient are consistent with locations inferred from the traditional criteria based on water mass properties, suitably modified to account for multiple frontal branches. Three regions are examined in detail: the Crozet Plateau, the Kerguelen Plateau and the Scotia Sea. These examples show how recognition of the multiple jets of the ACC can help resolve discrepancies between previous studies of ACC fronts.