《厦门大学学报（自然科学版）》

以航次实测温、盐剖面数据为基础,对2015年7—8月珠江冲淡水扩展特征进行观测,并结合定点浮标风场以及漂流浮球的数据,对影响其扩展特征的主要因素进行分析,从而为研究珠江口碳、营养盐等物质的输移、分布等过程提供基础资料.研究发现珠江冲淡水调查期间存在两种扩展形态:离岸东向扩展和沿岸西向扩展.在西南季风稳定时,冲淡水主要以离岸东向扩展为主,水平扩展范围距珠江口超过350 km且垂向覆盖厚度(即盐度小于32的水层厚度)约为5～20 m,表层32 等盐线与南海北部陆架内50 m等深线一致.夏季稳定的西南季风有利于珠江冲淡水在Ekman输运下持续被带离河口,当珠江冲淡水跨越20 m等深线后受到沿岸东北向流和离岸运动的共同作用,以东向扩展为主; 但在西南季风减弱甚至发生风向的变化时,珠江冲淡水的离岸运动也随之减弱,从而在20 m等深线以内的珠江口区域形成堆积,在地转偏向力的作用下,此时珠江冲淡水的扩展形态以沿岸西向为主.

This study investigates the extension characteristics of the Pearl River diluted water based on hydrological data collected in a summer cruise during July 18 to August 5,2015.Together with the wind field data from the mooring buoy and data from the drift floats,we analyze the main factors affecting the extension characteristics.It provides the basic data for studying how the carbon,nutrient and other materials are distributed and transported in the Pearl River Estuary.Cruise observation data reveal that the Pearl River diluted water had two extension forms from July to August in 2015,one was offshore eastward extension and the other was alongshore westward extension.When southwesterly monsoon is stable,the diluted water mainly extends offshore eastward,with the extension distance farther than 350 km from the Pearl River Estuary,the vertical coverage thickness(that is the thickness of water with the salinity less than 32)of about 5-20 m,and the 32 salinity isohaline consistent with the 50 m isobath on the continental shelf of the northern South China Sea.The main cause of this eastward extension is the combined effect of offshore Ekman transport by stable southwesterly monsoon in summer and alongshore northeastward current when the Pearl River diluted water crosses the 20 m isobath.However,when the southwesterly monsoon is weakened,or even the wind direction changes,eastward extension of the diluted water weakens till it disappears,and the alongshore westward extension is enhanced.Southeasterly wind may impede the offshore movement of the diluted water.Therefore,the diluted water accumulates in the Pearl River Estuary area inside the 20 m isobath,and the Pearl River diluted water extension mainly moves alongshore westward by Coriolis effect.

引言
1 航次观测数据
2 结果与讨论
3 结论

图1 2015年夏季航次的站位分布<br/>Fig.1 Distribution of survey stations during the cruise in summer 2015

图1 2015年夏季航次的站位分布
Fig.1 Distribution of survey stations during the cruise in summer 2015

图2 漂流浮球示意图<br/>Fig.2 The drift float diagram

图2 漂流浮球示意图
Fig.2 The drift float diagram

图3 站位F802温、盐的垂直分布<br/>Fig.3 Vertical distributions of temperature and salinity at station F802

图3 站位F802温、盐的垂直分布
Fig.3 Vertical distributions of temperature and salinity at station F802

图4 珠江口表层盐度的平面分布<br/>Fig.4 Horizontal distribution of surface salinity in the Pearl River Estuary

图4 珠江口表层盐度的平面分布
Fig.4 Horizontal distribution of surface salinity in the Pearl River Estuary

图5 2F801站2015年7月29日22:00—7月31日12:00盐度垂直分布的时间变化<br/>Fig.5 Time variations of vertical distribution salinity at the station 2F801 from 22:00 July 29 to 12:00 July 31,2015

图5 2F801站2015年7月29日22:00—7月31日12:00盐度垂直分布的时间变化
Fig.5 Time variations of vertical distribution salinity at the station 2F801 from 22:00 July 29 to 12:00 July 31,2015