Vertical Eddy Fluxes in the Southern Ocean

Abstract

The overturning circulation of the Southern Ocean has been investigated using eddying coupled ocean-sea ice models. The circulation is diagnosed in both density-latitude coordinates and in depth-density coordinates. Depth-density coordinates follow streamlines where the Antarctic Circumpolar Current is equivalent barotropic, capture the descent of Antarctic Bottom Water, follow density outcrops at the surface, and can be interpreted energetically. In density-latitude coordinates, wind-driven northward transport of light water and southward transport of dense water are compensated by standing meanders and to a lesser degree by transient eddies, consistent with previous results. In depth-density coordinates, however, wind-driven upwelling of dense water and downwelling of light water are compensated more strongly by transient eddy fluxes than fluxes because of standing meanders. Model realizations are discussed where the wind pattern of the southern annular mode is amplified. In density-latitude coordinates, meridional fluxes because of transient eddies can increase to counter changes in Ekman transport and decrease in response to changes in the standing meanders. In depth-density coordinates, vertical fluxes because of transient eddies directly counter changes in Ekman pumping.

Role of Mesoscale Eddies in Cross-Frontal Transport of Heat and Biogeochemical Tracers in the Southern Ocean

“…Finally, standing meanders distort the front meridionally, increasing the surface of exchange at the front. These ideas have been hypothesized or discussed in several recent studies, which all tend to show that eddy activity is augmented in the presence of standing meanders (Naveira Garabato et al 2011; Thompson and Sallée 2012;Zika et al 2013;Abernathey and Cessi 2014). In particular, using numerical simulations with and without topography, Abernathey and Cessi (2014) showed that cross-frontal eddy heat flux was stronger in the experiment with topography due to the presence of standing meanders.…”

The Energetics of Southern Ocean Upwelling

“…An Eulerian zonal average of the meridional flow yields a strong Deacon cell (Döös and Webb 1994), which bears little resemblance to tracer pathways. We therefore analyze the physical circulation in latitude-density space, which can be written [following Zika et al (2013)] as…”

“…This diagnostic is computed online during the simulation. The depth-density streamfunction, again following Zika et al (2013), is written as…”

“…We analyze these simulations from an energetic perspective, focusing on the evolution of available potential energy of the model, as outlined in section 2 below. We then aim to connect this energetic diagnosis with the overturning circulation, using a combination of the latitude-density (often called the residual) overturning streamfunction and the depth-density streamfunction (Nurser and Lee 2004;Nycander et al 2007;Zika et al 2013; see section 2d). The model is described in section 3, and the results are described in section 4.…”

Acceleration of the Antarctic Circumpolar Current by Wind Stress along the Coast of Antarctica

“…Its consequent steeply sloping isopycnals connect a huge fraction of the deep ocean to the atmosphere (Rintoul et al 2001;Johnson and Bryden 1989). Turbulent processes, themselves intimately linked to the ACC, play a major role in exchanges between near-surface waters and the ocean interior (Marshall 1997;Zika et al 2013). Knowledge of what drives the ACC is thus critical to our understanding of ocean circulation and climate.…”