Krüger, Matthias (2013) Zirkulation und Vermischung in der Agulhas Retroflection während der ARC 12 Messkampagne. (Bachelor thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 29 pp.

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Abstract

This Bachelor thesis deals with the circulation and diapycnal mixing in the Agulhas region at the southern tip of Africa. This region is characterized by fast and variable current velocities. Microstructure, salinity, temperature, and current velocity data of the ARC 12 expedition are used. The spatial distributions of diapycnal mixing and current velocities are investigated. Additionally the variability of the background conditions is observed as diapycnal mixing is related to it. The analyzed microstructure data of the ARC 12 expedition show significant variations at the different stations. Elevated levels of turbulent dissipation rates (ǫ) are observed at all stations below the mixed layer. Here, the magnitudes reach values of 10−7W/kg, in some cases 10−6W/kg. Increased activities of turbulent mixing between 100 dbar and 500 dbar are observed at the stations along the 40◦ S section. The values of the turbulent dissipation rates in these depths are in the order of 10−7W/kg. In a depth of 200 dbar turbulent eddy diffusivities (Kp) of 10−4m2/s occur. Between 400 dbar and 1000 dbar the values are constant at about 4 · 10−5m2/s. The analysis of velocity shear profiles indicates that internal waves cause the observed elevated levels of dissipation rates and turbulent eddy diffusivities. The results show a turbulent diffusivity in midwaters that is increased by a factor of 4 compared to commonly observed values at this depth. It suggests that the Agulhas Retroflection is a hotspot of diapycnal mixing in the Southern Ocean.

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