[M-IS20] Global climate change driven by the Southern Ocean and the Antarctic Ice Sheet

[MIS20-P02] Oceanic mixing on the continental slope of the Australia-Antarctic Basin

*Katsuro Katsumata¹ (1.JAMSTEC)

Keywords:vertical and horizontal mixing, cabbelling and thermobaricity, meridional overturning circulation

Diapycnal and isoycnal diffusivities are estimated from the data obtained onboard R/V Kaiyomaru cruise KY18-04 on the continental slope, south of the Australia-Antarctic Basin. Displacement of isopycnal surface (strain) is estimated from CTD (conductivity-temperature-depth profiler) and vertical difference of horizontal currents (shear) is estimated from LADCP (lowered acoustic Doppler current profiler). Application of the Gregg-Henyey-Polzin parameterisation yields diapycnal diffusivities associated with breaking of internal waves at 9x10^-5m²/s (on 1028.05 kgm^-3 isopycnal) and 1.4x10^-4m²/s (on 1028.30 kgm^-3 isopycnal). Assuming the steady advection-diffusion balance, the isopycnal diffusivity is estimated at 20 m²/s and 560 m²/s, respectively. These values are smaller than the isopycnal (horizontal) diffusivities estimated within the Antarctic Circumpolar Current region. However, downward vertical transport caused by cabbeling (density increase explained by nonlinearity of the equation of state for sea water) in consequence of the isopycnal mixing is comparable to the vertical transport caused by the mechanical mixing by internal waves.