Variability and mesoscale activity of the Southern Ocean fronts: Identification of a circumpolar coordinate system

Recent studies have highlighted the filamented nature of the jets associated with the Antarctic Circumpolar Current (ACC). However, the nature, variability and continuity of the ACC fronts remain a topic of debate, in part because different methods provide different perspectives on this complex current system. The goal of this study is to identify a circumpolar coordinate system or reference frame that accounts for the multiple jets of the ACC and that would be suitable for future studies of cross-front fluxes. A new methodology is developed and tested using simulations from several ocean general circulation models (OGCMs). The method uses subsurface temperature criteria and transport maxima to identify five primary circumpolar fronts. The frontal structure derived using this approach is compared to the sea surface height (SSH) contour approach of Sokolov and Rintoul (2007) and a hybrid of the two methods is proposed. Strengths and weaknesses of the different approaches are summarized. We show that the hybrid approach defines a coordinate system that helps explain the circumpolar structure and variability of the ACC fronts and is relevant for the estimation of cross-front fluxes. Fronts defined in this way show behaviour largely consistent with previous studies, including along-front changes in intensity, splitting and merging of fronts, large meridional displacements and unstable behaviour in the vicinity of large bathymetric features.

► Develop a new definition to identify the ACC fronts in OGCMs, combining subsurface hydrography, depth integrated properties and SSH fields. ► Find a number of circumpolar fronts which correctly represents the unstable front behaviours in the Southern Ocean. ► Demonstrate the main role of local bathymetric control in the destabilisation of the fronts and mesoscale activity development. ► Underline the usefulness of the coordinate system to study the climatic impact of mesoscale activity on meridional heat fluxes. ► Confirm the relevance of the SSH contour method developed by Sokolov and Rintoul (2002).