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The MST (Microstructure-Turbulence) Profiler is a newly developed operational microstructure measuring system, specially designed for marine and limnic turbulence measurements. The profiler can be used for sinking and uprising measurements and is equipped with a new type of current shear sensor. We have tested the MST Profiler in several field measuring campaigns in deep Alpine lakes. The investigations were focused on the internal vibration level of the profiler and its lower detection limit for dissipation rate estimates (pseudo dissipation). The upper detection limit was estimated based on the geometry of the shear sensor. The test measurements gave no indication of pronounced internal profiler vibrations interfering with dissipation measurements. The pseudo dissipation level (noise) of the profiler was found to be as low as 5 · 10 -12 W/kg under quiet conditions at sinking velocities below 0.4 m/s. At 0.8 m/s sinking velocity, a pseudo dissipation of 4 · 10 -11 W/kg was obtained. At rising measurements with additional sources of profiler vibrations due to influence of the cable the pseudo dissipation is about twice that for sinking measurements. For the upper detection limit which can be measured without correction for unresolved variance of the shear spectrum, a value of 10 -4 W/kg was estimated.

The mixing regime of the upper 180 m of a mesoscale eddy in the vicinity of the Antarctic Polar Front at 47 S and 21 E was investigated during the R.V. Polarstern cruise ANT XVIII/2 within the scope of the iron fertilization experiment EisenEx. On the basis of hydrographic CTD and ADCP profiles we deduced the vertical diffusivity K z from two different parameterizations. Since these parameterizations bear the character of empirical functions, based on theoretical and idealized assumptions, they were inter alia compared with Cox-number and Thorpe-scale related diffusivities deduced from microstructure measurements, which supplied the first direct insights into turbulence of this ocean region. Values of K z in the range of 10 À4 -10 À3 m 2 s À1 appear as a rather robust estimate of vertical diffusivity within the seasonal pycnocline. Values in the mixed layer above are more variable in time and reach 10 À1 m 2 s À1 during periods of strong winds. The results confirm a close agreement between the microstructure-based eddy diffusivities and eddy diffusivities calculated after the parameterization of Pacanowski and

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