南极威德尔-斯科舍汇流区上层湍流混合特征及其与水团和环流的联系

Turbulent mixing and its relationship with water mass and circulation in the upper ocean of the Weddell-Scotia Confluence,Antarctica

利用中国第32次南极科学考察队于2015年12月至2016年1月在南极威德尔-斯科舍汇流区获得的湍流微结构、温盐深仪和下放式声学多普勒海流计观测资料,分析了该海域上层海洋(30~500 dbar)的湍流混合空间分布特征。结果显示,湍动能耗散率(ε)和湍扩散系数(K_(ρ))分布呈现明显的区域性特征,与当地的水团和环流分布密切相关。鲍威尔海盆边缘-南奥克尼海台区的表层水体因海冰融水的加入而层化加强,湍流混合受到抑制,其混合水平在整个调查海域中最弱,K_(ρ)普遍小于10^(-4)m^(2)×s^(-1);布兰斯菲尔德海峡区的水团主要由邻近海域的水团变性组成,上层海洋的层结不稳定,K_(ρ)平均值约为1.2×10^(-4)m^(2)×s^(-1);埃斯佩里兹海槽区是斯科舍海与威德尔海水交换的主要通道,在复杂流场与粗糙地形的共同作用下,水体混合剧烈,整个上层剖面的K_(ρ)基本在3.2×10^(-4)~3.2×10–3 m^(2)×s^(-1)之间,强混合维持了该海域相对均匀的温度和盐度垂向结构;斯科舍海南部陆坡区存在不同温盐性质水体的交汇入侵,引起混合增强,K_(ρ)约1.6×10^(-4)m^(2)×s^(-1)。本次观测结果表明,海水层化状态、垂向剪切流不稳定和水团交界处的热盐入侵对南大洋上层海洋湍流混合空间分布有重要影响。

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)m^(2)×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)m^(2)×s^(-1).Striking diffusivity profiles with values range from 3.2×10^(-4)to 3.2×10^(–3) m^(2)×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)m^(2)×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.