2011年初冬南极普里兹湾冰间湖区上层水体结构演化研究

利用5头活动于南极普里兹湾的象海豹携带的CTD观测获得的2011年3—6月埃默里冰架前缘冰间湖区域海水温盐剖面数据, 研究了该海域上层水体结构在初冬的演化过程。结果显示, 可将该演化过程分为三个阶段：第一阶段海水温度从层化到均匀, 3月下旬次表层仍维持暖水特征, 随着表层海水冷却作用, 次表层暖水逐渐消失, 上下水体温度趋于均匀并接近冰点, 温度剖面从“逆温型”演变到“均匀型”; 第二阶段海水盐度从层化到上下均匀, 也就是从“均匀型”演变到“渐变型”, 海水结冰析盐过程使上层海水盐度增加, 增强垂直对流混合, 上下层盐度达到均匀; 第三阶段冷却结冰持续, 海水盐度继续增大, 形成盐度随深度减小, 温度随深度增大的“渐变型”结构。根据温盐剖面数据计算三个阶段的海-气之间的热通量分别是－90.93、－82.20和－43.44 Wm^-2。考虑海水盐分的增加主要源于海冰形成, 由此推算三个阶段内平均的海冰形成速率分别是5.4、4.9和2.5 cm d^-1。在南极初冬时期, 随着海水上层低温高盐化演变持续, 海水向大气释放的热通量逐渐减少, 海冰形成速率也呈减少趋势。

The evolution of upper water structure in the Prydz Bay polynya region during Antarctic winter, 2011

Hydrographic data collected during the early Antarctic winter 2011 by CTD tags fitted to five elephant seals were analyzed to study the evolution of the upper water layer in the Prydz Bay polynya adjacent to the Amery ice shelf. The evolution of upper ocean structure could be divided into three stages. First, temperature shifted from a stratified profile to homogeneity. Warm water was still present in the subsurface in late March. This warm water gradually disappeared with cooling of the surface water, so the temperature profile evolved from temperature inversion to homogeneity at temperatures close to freezing. Second, salinity shifted from a stratified profile to homogeneity. Salinity increased with the freezing of seawater, which strengthened vertical convection and resulted in homogeneous salinity throughout the upper water layer. Third, seawater continued to cool and salinity continued to increase. Stratified profiles of temperature and salinity were reestablished. With increased depth, salinity decreased and temperature increased. Air–sea heat fluxes calculated from temperature and salinity profiles during the first, second, and third stages were -90.93 W m^-2, -82.20 W m^-2, and -43.44 W m^-2, respectively. The increase in salinity was mainly the result of sea ice formation, and the sea ice formation rates were 5.4 cm d^-1, 4.9 cm d^-1, and 2.5 cm d^-1, respectively. In summary, the present study demonstrated that during the early Antarctic winter, as temperatures in the upper water layer continue to decrease and salinity increases, the heat flux released from ocean to atmosphere and the sea ice formation rate gradually decrease.