Observed Mixing Processes in Prydz Bay, Antarctica during Austral Summer

Prydz Bay is a major Antarctic Bottom Water production region adjacent to a major cold cavity ice shelf. Its underlying mixing processes are little known, though they determine the intensity of water mass transformation. Using microstructure measurements, we reveal detailed regional variations of dissipation and mixing in Prydz Bay during summer. In the upper layer, turbulence dominates the continental shelf, presenting weak dissipation rate of thermal variance χθ ( O (10 −10 )°C 2 s −1 ), but showing elevated dissipation rate of turbulent kinetic energy ε ( O (10 −8 ) W kg −1 ) and thermal eddy diffusivity K θ ( O (10 −4 ) m 2 s −1 ). On the continental slope, diffusive convection prevails, with one-order greater χθ and one-order smaller ε and K θ . On the shelf break, turbulence and diffusive convection coexist, with elevated ε , χθ , and K θ reaching the orders of 10 −8 W kg −1 , 10 −8 °C 2 s −1 , and 10 −4 m 2 s −1 , respectively. Tidal current’s encountering with the ice shelf, background current’s impinging on the rough topography, and the intrusion of modified Circumpolar Deep Water all contribute to these spatial variations. The dissipation ratios Γ for both turbulence (0.05) and diffusive convection (0.14) are statistically smaller than those in waters of mid and low latitudes, because water in Prydz Bay is primarily stratified by salinity, hence the strong temperature gradient is associated with a weak stratification. Based on these features, we propose a new indicator to differentiate turbulence and double diffusion. This study is helpful for better understanding Antarctic mixing processes, and their contributions to local water mass transformation and to global ocean circulation and climate.