Upper-ocean vertical mixing in the Antarctic Polar Front Zone

The nnxing regime of the upper 180 m of a mesoscale eddy in (he vicinity of the Antarctic Polar Front at 47 degrees S and 21 degrees E was investigated during the RN. 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 diffLISivity K-z from two different parameterizations. Since these parameterizations bear the character of empirical functions, based oil 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(-4)-10(-3) m(2) s(-1) 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(-1) m(2) s(-1) 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 Philander [1981. Journal of Physical Oceanography 11, 1443-1451]. (c) 2005 Elsevier Ltd. All rights reserved.