Observational analysis on 3D distribution and seasonal variation of thermohaline characteristics in the Zhanjiang Bay
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摘要: 利用2017年1−12月的现场观测数据,分析了湛江湾温盐的三维空间结构及季节变化特征。结果表明:(1) 2017年湛江湾各站位年平均温度为23~27℃、盐度为19~27、位势密度为11~17 kg/m3、浮性频率(N2)为7×10−5~5×10−3 s−2。浮性频率的垂向结构及水平分布与温度分布类似,而位势密度则与盐度的变化趋势几乎一致;(2)温度季节变化明显,夏季最高,秋季次之,冬季最低,冬夏温差最大达15℃,而盐度季节变化则不大。相较于季节引起的变化,涨落潮对温度以及盐度影响较小。温度跃层夏季最强,10 m处温度最大梯度可达到0.7℃/m,春秋季温跃层抬升至5 m附近,冬季水体上下混合均匀。夏季和秋季存在明显的盐跃层,盐度梯度最大可达到1.1 m−1。跃层上下温盐的季节变化规律一致;(3)水平分布上,从湾顶区、湾颈区、大堤区、浅滩区到湾口区,温度递减,盐度递增,湾顶区和湾口区平均温度差为2.3℃,盐度差为2.7。温盐图分析显示,不同季节水体呈现为不同的温盐条带,湾口区基本为低温、高盐水体,而湾顶区基本为高温、低盐水体,其他区域水体介于上述两者之间。Abstract: Using in-situ hydrographic observations from January to December 2017, 3D thermohaline structure and seasonal variation in the Zhanjiang Bay is investigated in this study. The results show that: (1) In 2017, the annual mean temperature is 23−27℃, the mean salinity is 19−27, the mean potential density is between 11−17 kg/m3, and the mean buoyancy frequency (N2) is about 7×10−5−5×10−3 s−2 in the Zhanjiang Bay. The vertical structure and horizontal distribution of N2 are similar to that of the temperature, while the distributions of potential density and salinity are similar. (2) The temperature has significant seasonality with the highest value in summer, followed by autumn, and the lowest in winter. The maximum temperature difference between winter and summer reaches 15℃, while the seasonal mean of the salinity varies slightly. The ebb and flood have less influence on temperature and salinity, comparing with their seasonal variations. The thermocline is the strongest in summer with the maximum gradient reaches 0.7℃/m at 10 m, whereas it shallows to 5 m in spring and fall, and the water well mixed in winter. The halocline is prominent in summer and fall, with the maximum gradient 1.1 m−1. The seasonal variation of the thermohaline in the upper layer and lower layer are consistent. (3) For the horizontal distribution, the temperature decreases and the salinity increases from the bay head, the mid bay, the bank region, the shoal region to the bay mouth. The average temperature difference between the bay head and the bay mouth is 2.3℃, and the salinity difference is 2.7. The temperature-salinity (θ-S) diagram shows banding distributions with one end as the low-temperature and high-salinity water in the bay mouth, one end as the high-temperature and low-salinity water in the bay head, and the other water masses are between them. Different bands are shown in different seasons.
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Key words:
- Zhanjiang Bay /
- thermohaline characteristics /
- 3D structure /
- seasonal variation
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图 10 各区域四季温盐图
灰色实线为等位势密度线;不同颜色的点分别代表各区域的站位;灰点为4个季节所有的观测值
Fig. 10 Seasonal temperature-salinity diagram in each region
The gray lines denote the potential density contours; the dots with different colors denote the observations in different regions; the gray dots denote all the observations in four seasons
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