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A model of the zonally averaged stratification and overturning in the Southern Ocean

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Citation:
Olbers, D. and Visbeck, M. (2005): A model of the zonally averaged stratification and overturning in the Southern Ocean , Journal of physical oceanography, 35 , pp. 1190-1205 .
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Abstract:

The ocean area south of the Antarctic Circumpolar Current (ACC) frontal systemis a region of major watermass modification. Influx of North Atlantic DeepWater (NADW), small scale mixing, eddy transport and diffusion as well as thefluxes of momentum and buoyancy at the sea surface combine in a complex arrayof processes to generate the unique stratification of the Southern Ocean withits southward uprising isopycnals and northward flux of Antarctic IntermediateWater (AAIW) and Antarctic Bottom Water. Comprehensive analytical models ofthis scenario are rare (\eg the recent model of Marshall and Radko 2003). Wedevelop and apply a model based on zonally and temporally averaged theory toexplain the conversion of NADW into AAIW with all of the above mentionedprocesses contained in an extremely simplified way. Eddies appear via a TEM(Transformed Eulerian Mean) approach with a conventional downgradientparameterization of the meridional density flux. The structure of the eddycoefficient is estimated from hydrographic and windstress data by a simpleinverse approach. Mixing is limited to a near-surface layer and treated in amost simple entrainment form. The model predicts the density stratification inthe Southern Ocean and the baroclinic transport of the ACC from the appliedwindstress and the surface density flux and unravels the role and importance ofthe different processes responsible for shaping the stratification (Ekman andeddy-induced advection and pumping, mixing, surface buoyancy flux andeddy-induced diffusion). We show that all these processes must be present toyield an agreement between the simulated stratification and the observed onebut details of their parameterization might not be too critical. The ACCtransport is shown to have a contribution forced by the local windstress aswell as another contribution relating to the nonlocal forcing by windstress anddensity flux over the entire Antarctic zone.

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