Characteristics of observed turbulent mixing across the Antarctic Slope Front at 140°E, East Antarctica

Abstract

The strength of mixing due to turbulence in the Antarctic Slope Front (ASF) region was investigated using CTD (conductivity-temperature-depth profilers) observations and direct measurements of turbulence conducted off Adelie Land, East Antarctica along 140°E from the 12th–14th February, 2005. The strongest horizontal gradient of the ASF was located below 300 m depth near the 1000 m isobath. The turbulent measurements revealed that the energy dissipation rate frequently exceeded 10−8 Wkg−1 on the continental shelf and upper slope regions. Turbulent diffusivities near the shelf break were higher than 10−3 m2s−1. Near the ASF the average turbulent heat flux was 5.7 Wm−2 and 1.1 Wm−2 across the temperature minimum layer to 250 m and from 300 to 600 m, respectively. The distribution of the high dissipation rate was consistently explained by the characteristic curve of the M2 internal wave emanating from the shelf break and continental slope. The water mass observed in the ASF below 300 m in the continental slope comprised Modified Circumpolar Deep Water and low salinity Shelf Water originating from either the upper layer of the Adelie Depression or the Adelie Bank, and produced by boundary mixing near the shelf break.