Abstract
Circulation in the Southern Ocean is unique. The strong wind stress
forcing and buoyancy fluxes, in concert with the lack of continental
boundaries, conspire to drive the Antarctic Circumpolar Current replete
with an intense eddy field. The effect of Southern Ocean eddies on the
ocean circulation is significant – they modulate the momentum balance
of the zonal flow, and the meridional transport of tracers and mass. The
strength of the eddy field is controlled by a combination of forcing
(primarily thought to be wind stress) and intrinsic, chaotic,
variability associated with the turbulent flow field itself. Here, we
present results from an eddy-permitting ensemble of ocean model
simulations to investigate the relative contribution of forced and
intrinsic processes in governing the variability of Southern Ocean eddy
kinetic energy. We find that variations of the eddy field are mostly
random, even on longer (interannual) timescales. Where correlations
between the wind stress forcing and the eddy field exist, these
interactions are dominated by two distinct timescales – a fast
baroclinic instability response; and a multi-year process owing to
feedback between bathymetry and the mean flow. These results suggest
that understanding Southern Ocean eddy dynamics and its larger-scale
impacts requires an ensemble approach to eliminate intrinsic
variability, and therefore may not yield robust conclusions from
observations alone.