Upper ocean mixing from shear microstructure and density inversions nearthe Walvis Ridge

The M180 cruise is part of the observational program of the TRR 181 'Energy Transfers in
Atmosphere and Ocean', and will focus on observe numerous energy compartments in
order to construct a regional oceanic energy budget for the southeast Atlantic. The study
area will be nearby the Walvis Ridge, a region of strong eddy activity and internal tides, in
the Eastern South Atlantic (0 -10 E, 30 -35 S). There, energy is converted from barotropic
to baroclinic tides at the seafloor. Additionally, in this region, the Agulhas leakage regularly
sheds eddies from the Agulhas current in the form of Agulhas rings that propagate slowly
northwestward. The location is, therefore, ideal for the study of interaction and links
between different energy compartments in the ocean and at the ocean-atmosphere
boundary.
The work will focus on energy dissipation and diapycnal mixing which, on the smallest
scales, drive the circulation in the ocean and is thus of highly significant for the global
meridional overturning circulation in the ocean and its deep ventilation. Time series
microstructure stations will be used to assess locally the temporal variability of mixing
and dissipation. From temperature, density and shear profiles obtained with a Vertical
Microstructure Profiler (VMP-250-IR), it will be possible to calculate the energy dissipation
rate of turbulent kinetic energy by assuming a statistically valid linear relationship
between the Thorpe Scale and the Ozmidov Scale. A direct comparison between the
inferred estimation of the dissipation rate and the directly calculated dissipation rate will
be presented. Moreover, in case a possible influence from Agulhas rings on dissipation is
detected, it will be investigated.