东海西部近海春、秋季水团特征分析

(1.厦门大学海洋与地球学院,近海海洋环境科学国家重点实验室,福建 厦门 361102; 2.南方海洋科学与工程广东省实验室(珠海),广东 珠海 519082)

东海西部近海; 水团; 模糊聚类法; T-S相似度法

Characteristics analysis of water masses in the western East China Sea in spring and autumn
ZHU Jia1,HU Jianyu1,2*,YANG Longqi1,CHEN Zhaozhang1,SUN Zhenyu1,2

(1.State Key Laboratory of Marine Environmental Science,College of Ocean and Earth Sciences,Xiamen University,Xiamen 361102,China; 2.Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519082,China)

western East China Sea; water mass; fuzzy clustering method; T-S similarity method

DOI: 10.6043/j.issn.0438-0479.202107031

备注

水团的季节分布特征及温盐结构的时空变化对近海水文、气候渔场位置有着重要影响.基于东海西部近海春、秋季航次的温盐深实测资料,分析了温度和盐度在平面和垂向上的空间分布特征,并采用模糊聚类法及T-S相似度法将调查海域的水团划分为5类:闽浙沿岸水、混合水、台湾暖流水、黑潮表层水及黑潮次表层水.闽浙沿岸水在沿岸呈带状分布,春季其与混合水交汇时形成狭长的温、盐锋面.黑潮表层水在春季占据远岸海域深度<75 m的绝大部分海域,并在50 m层向岸延伸出两条高盐水舌; 而在秋季仅分布在调查海域东北角,在东南部则被台湾暖流水取代.黑潮次表层水在春、秋季均存在跨陆架的涌升现象,秋季涌升至50 m层,并将台湾暖流水截断为南、北两部分.

Objective: The seasonal distributions of water masses and the temporal and spatial variations of temperature-salinity structure have important influences on the hydrology, climate and fishery sites of offshore waters. Previous researches mainly used classical methods to analyze the water masses in the western East China Sea in summer and winter. To reveal the less understood structure of water masses in the western East China Sea in spring and autumn, we collect conductivity-temperature-depth (CTD) data during spring and autumn cruises in the western East China Sea and analyze the spatial distributions of temperature and salinity, from which five water masses are classified using the fuzzy clustering method and T-S similarity method.
Methods: Water masses are preliminarily classified using the fuzzy clustering method. In order to present a more realistic distribution of water masses, the T-S similarity method is applied to further quantify the water sample by clearly specifying the boundaries between water masses. Given that fluid generally moves along the isopycnal surface, the T-S similarity method defines a T-S similarity number (TSSN) by calculating the distance between water samples and typical water mass curves on the isopycnal surface. TSSN ranges between 0 and 1. The closer the TSSN value is to 0, the higher the similarity of the water sample is to the typical water mass.
Results: The western East China Sea is classified into five water masses: the Min-Zhe coastal water, the mixed water, the Taiwan Warm Current water, the Kuroshio surface water and the Kuroshio subsurface water. The Min-Zhe coastal water is distributed in a zonal pattern along the western coast, forming a long and narrow strong front of temperature and salinity when it intersects with the mixed water in spring. The Kuroshio surface water occupies the offshore area shallower than 75 m in spring, with two high salinity water tongues extending to nearshore at the 50 m layer. In autumn, the Kuroshio surface water is only distributed northeast of the investigated region and is replaced by the Taiwan Warm Current water in the southeast. The Kuroshio subsurface water upwells across the continental shelf in both spring and autumn, and it upwells to 50 m in autumn, cutting off the Taiwan Warm Current water into two parts.
Conclusion: According to the temperature-salinity structure and classification of water masses derived from the observation results of the two cruises in April 2019 and November 2018, it is found that the distribution of temperature and salinity in the western East China Sea has spatial differences in horizontal and vertical directions, and the distribution of water masses also shows clear seasonal variation. Future measurement data in summer and winter in this region, as well as other parameters except for temperature and salinity may support the in-depth discussion of intact seasonal variation of water masses in the western East China Sea.

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