Circulation and Stirring in the Southeast Pacific Ocean and the Scotia Sea 2 sectors of the Antarctic Circumpolar Current

D. Balwada, K.G. Speer, J.H. LaCasce, W.Brechner Owens, J. Marshall, and R. Ferrari
Journal of Physical Oceanography,

The large-scale deep circulation and eddy diffusivities in the Southeast Pacific Ocean and Scotia Sea sectors between 110oW and 45oW of the Antarctic Circumpolar Current (ACC) are described based on a unique lagrangian dataset spanning a large sector of the Southern Ocean. The circulation and lateral stirring are estimated using subsurface RAFOS float data collected during the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). The mean flow, adjusted to a common 1400m depth, shows the presence of jets in the time-averaged sense with speeds of 6cm/s in the South East Pacific Ocean and upwards of 13 cm/s in the Scotia Sea. These jets appear to be locked to topography in the Scotia Sea but, aside from negotiating a seamount chain, are mostly free of local topographic constraints in the Southeast Pacific Ocean. The EKE is higher than the MKE everywhere in the sampled domain by about 50%. The absolute magnitude of the EKE increases drastically (by a factor of 2 or more) as the current crosses over the Hero Fracture Zone and Shackleton Fracture Zone into the Scotia Sea. The isopycnal stirring shows lateral and vertical variations with local eddy diffusivities as high as 2500m 2/s at 700m decreasing to 1500m 2/s at 1800m in the Southeast Pacific Ocean and higher vales in the Scotia Sea. However, when the action of jets is taken into account, the cross-ACC diffusivity reduces significantly, with values of 500m 2/s and 1000m 2/s at shallow and deep levels respectively.