双扩散在南极文森湾海域热盐结构演变中的作用

EFFECT OF DOUBLE DIFFUSIVE CONVECTION DURING THE EVOLUTION OF SEAWATER THERMOHALINE STRUCTURE IN VINCENNES BAY,ANTARCTICA

利用22头象海豹携带的CTD观测到的2012年3—4月南极文森湾中西部海域的海水温盐剖面数据,研究了双扩散效应在海水热盐演变过程中的作用。结果显示,该海域双扩散效应显著,其中"扩散对流"作用在水柱中所占比例超过50%,并普遍存在于500—800 dbar深度的深层水中;"盐指对流"作用在水柱中所占比例不超过10%,存在于300—500 dbar的中层水中;随着时间进入南极冬季,海水结冰盐析过程会使水体中重力不稳定状态加剧。"扩散对流"会产生向上的热通量和盐度通量,热通量大约在0.02—0.5 W·m^(–2),盐度通量平均在10–8 m·s^(–1)左右;"盐指对流"则会产生向下的热通量和盐度通量,平均热通量约为–0.5 W·m^(–2),平均盐度通量约为–10–8 m·s^(–1)。在结冰初期,文森湾陆架海域的海表结冰过程对低温高盐水体的产生具有补充作用,进而通过扩散对流作用使得高密度陆架水(DSW)在水体内部得到补充生长与积累。因此,双扩散作用对于该海域高密陆架水的形成有不可忽视的贡献。

Based on seal CTD data obtained in mid-western areas of Vincennes Bay during March–April 2012,the effect of double diffusive convection during the evolution of the seawater thermohaline structure during the early freezing period was evaluated.Results showed that the effect of double diffusion convection was substantial.The proportion of "diffusion convection" throughout the entire water column was >50%,and strong "diffusion convection" persisted in the deep water from 500 to 800 dbar.The proportion of "salt finger convection" in the water column was ≤10% and it occurred in the mid-layers between 300 and 500 dbar.As the Antarctic winter progresses,brine rejection during sea ice formation makes the water increasingly gravitationally unstable."Diffusion convection" produces upward fluxes of heat and salinity.The heat flux is in the range of 0.02–0.5 W·m^(-2),and the average salinity flux is about 10^(-8) m·s^(-1)."Salt finger convection" produces downward fluxes of heat and salinity; the average heat flux is about -0.5 W·m^(-2) and the average salinity flux is about -10^(-8) m·s^(-1).During the early freezing period,continuous cooling and brine rejection force the production of dense water with low temperature and high salinity.Double diffusion convection(mainly diffusive convection) reforms the water properties,making the entire water column denser.Therefore,the contribution of double diffusion convection on the formation of dense shelf water in Vincennes Bay is crucial.