长江口海域水文环境要素分布及溶解氧垂向输运

DISTRIBUTION OF HYDROLOGICAL ENVIRONMENTAL ELEMENTS AND VERTICAL TRANSPORT OF DISSOLVED OXYGEN IN CHANGJIANG RIVER ESTUARY

本文基于2016年长江口海域(舟山绿华山)的连续观测数据,分析了该海域水文环境要素分布,并估算了溶解氧跨跃层垂向输运。本次观测发现,水体的温度、盐度和溶解氧剖面具有明显的分层结构,三者跃层具有相同的变化趋势且主要受潮流变化影响。通过计算,得到跃层浮性频率的平方(N2)在10–3-10–2/s2之间,剪切的平方(S^2)介于10^-5-10^-2/s^2。潮流活动会激发水体剪切不稳定促进水体中溶解氧的垂向交换。最后,采用简化的一维溶解氧垂向输运模型,得到观测周期内跨跃层输运的溶解氧的含量为4.75mmol/(m^2·d),佐证层化是长江口海域出现氧亏损现象的主要原因之一。

The data of this paper are derived from continuous observation in Changjiang(Yangtze)River estuary off Lvhuashan,Zhoushan,Zhejiang in 2016.We analyzed the distribution of hydrological environmental elements,and estimated the vertical transport of dissolved oxygen across thermocline.From the observation,we found that temperature,salinity,and dissolved oxygen in the profile of water column show obvious stratification structure,and the thermocline has the same variation trend that mainly affected by the change of tidal current.We determined by calculation the buoyancy frequency square(N^2)to be 10^-3-10^-1/s^2 and the shear square(S^2)10^-5-10^-2/s^2.In addition,we found that tidal activity could stimulate the shear instability and promote vertical exchange of dissolved oxygen in water.Using the simplified model of one-dimensional vertical transport of dissolved oxygen,we calculated the cross-thermocline transport of dissolved oxygen to be 4.75 mmol/(m^2·d),proving that stratification is formed due mainly to oxygen depletion in the Changjiang River estuary waters.