Abstract:

Based on the turbulence microstructure, Conductivity-Temperature-Depth profiler and Lowered Acoustic Doppler Current Profiler data obtained by the 32nd Chinese National Antarctic Research Expedition in the Weddell-Scotia Confluence (WSC) from December 2015 to January 2016, the spatial distribution characteristics of turbulent mixing in the upper ocean (30–500 dbar) were analyzed. Results showed that turbulent kinetic energy dissipation (ε) and turbulent eddy diffusivity (K_ρ) have regional features closely related to local characteristics of the water mass and circulation. In the region of the Powell Basin edge and South Orkney Plateau, strong surface stratification strengthened by inputs of sea ice meltwater impedes turbulent mixing, which results in diffusivity to be lower than 10^–4 m²×s^–1, the lowest mixing level in the studied area. In the region of Bransfield Strait, where intrusion and modification of water masses from adjacent seas result in relatively weak stratification, the spatially-averaged (30–500 dbar) K_ρ is 1.2×10^–4 m²×s^–1. Striking diffusivity profiles with values range from 3.2×10^–4 to 3.2×10^–3 m²×s^–1, exceeding the levels in the other subregions, were found in the Hesperides Trough, the main channel of water exchanges between Scotia Sea and Weddell Sea. Extensive interactions between the complex circulations and rough/steep topography intensify turbulent mixing and enhance the homogeneity of the vertical thermohaline structure. On the slope of the South Scotia Sea, intrusions of water with different temperature and salinity properties, cause remarkably high mixing, with an average K_ρ of around 1.6×10^–4 m²×s^–1. Further analysis revealed that the seawater stratification, instability due to vertical shear of the flow and thermohaline intrusion are important factors influencing the turbulent mixing in the WSC area.

Key words:

turbulent mixing, shear instability, thermohaline intrusion, Weddell-Scotia Confluence, Antarctica