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Exploring diapycnal mixing in the Southern Ocean (MIXCLIM)
Start date: 01 Mar 2009, End date: 30 Sep 2009 PROJECT  FINISHED 

"Because they control the rate at which water sinking at high latitudes returns to the surface in the Southern Ocean, mixing processes govern the capacity of the Southern Ocean to take up CO2 and the sensitivity of the Meridional Overturning Circulation (MOC) to climate change. Mixing processes also play a key role in the formation and meridional transport of Southern Ocean mode and intermediate waters. Recent in situ estimates of turbulent mixing indicate remarkably intense and widespread turbulent kinetic energy dissipation in four Southern Ocean “hotspots”. Three different mixing processes (breaking of internal waves generated by tidal, mean or atmospheric-depression induced flow interacting with topography) are suspected to generate diabatic mixing, but their relative contributions both in terms of their magnitude and distribution in the vertical remain unclear. Furthermore, these processes are not taken into account in climate and ocean circulation models. The aim of the present project is thus to quantify the main different diabatic mixing processes in the Southern Ocean interior and to parameterise their effects within ocean models. Simple consideration of linear wave propagation and dissipation of internal waves in a stratified fluid will be used to create specific parameterisations of the missing physics in an eddy resolving model focussed around the Kerguelen Plateau.The parameterisations will be tested and refined by the comparison of model data with ARGO float data. The respective contributions of the three different mixing processes will be quantified and introduced in a global ocean circulation model in order to assess their impact on the MOC and CO2 uptake. This modelling study is very timely since it would benefit and complement observations planned by NOCS: the SOFINE project that will measure vertical diffusivity in the Kerguelen region and the DIMES cruises that will measure isopycnal and diapycnal mixing in the Drake Passage and the Scotia Sea"
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