东海北部夏季水文特征分析

A study of the Hydrographic Features in summertime in the Northern East China Sea

利用 1990年 8月获得的水文和化学调查资料证实 ,在东海东北部海区存在着气旋型涡旋 ,由此形成的冷水中心从底层上升至 30 m水层 ,位于 32°N和 12 5°4 5′的交叉区域 ,基本上同于1972年的地理位置 ,但强度相对较弱。并首次利用 18O资料论证调查海区内表层水系长江冲淡水团向东北平流的结果 ,再用外推法获得长江淡水的 δ18O值应等于 - 8.0。根据密度资料判定表面混合层的厚度大约为 10 m。

Hydrographic and chemical data collected in the Northern East China Sea during August 1990 have been used to describe the spatial distributions of several water masses in the study area. A relative cold (16~19℃) saline (34.0<S<34.5), Huanghai Warm Current (HWC) extended into the Huanghai Sea at depths below 40m from its east side to the northwest. A relative saline (S≈32.5;15℃<t<17℃), Huanghai Coastal Current (HCC) flowed into the southeast from the western flank of this region. Beneath seasonal thermocline (30m or so), the bottom layer in the west part of the study area was occupied mostly by the Northeastern East China Sea Bottom Water (NE), characterized by salinity of 32.8<S<34.0 and temperature of 14℃<T<15℃. In short, our in situ data clearly revealed the existence of a cyclonic (anticlockwise) eddy centered at about 32°N, 125°45′E throughout the water column below 30m layer, which is a repeatedly observed Hydrographic phenomenon of the Northern East China Sea in summer. It is also observed that there is a surface circulation, existing in the upper layer above 20m, the pattern of which is consistent with geostrophic feature. Furthermore, both δ 18O and T/S data were used to distinguish the Changjiang Diluted Water (CDW), spreading over 10m-thick upper mixed layer. Simultaneously, the fact the value ofδ 18O equals -8.0 for the Changjiang fresh water was first obtained by means of extrapolation.