黑潮次表层水向北越过长江口外水下河谷的动力机制及去向研究

In the recent years, jellyfish blooms have increased. It is reported that offshore of the Changjiang River is one of its principal breeding places, and is the area where the pelagic stages of jellyfish appear earliest in the Yellow Sea and East China Sea in late May and early June. Both the temperature and salinity can significantly influence the growth of the jellyfish ephyrae. On the other hand, it is pointed out that the Kuroshio subsurface water (KSSW) intrudes into the East China Sea and reaches as far as the submarine canyon off the Changjiang River mouth. The KSSW originates from the subsurface water (100-300 m) of Kuroshio east of Taiwan, whose water properties, such as temperature, salinity, concentration of nutrient and dissolved oxygen are significantly different to those of coastal water. Due to the larger value of temperature and salinity relative to the coastal water, the KSSW can considerably influence the breading place of the jellyfish. However, the key mechanism controlling the cross-canyon movement of the KSSW remains unclear, and the destiny of KSSW after crossing the canyon is unknown. Therefore, we need the “Study on the key mechanism and destiny of the Kuroshio Subsurface water crossing a submarine canyon off the Changjiang River mouth” to clarify the key process and mechanism of KSSW crossing the canyon. If the spatial and temporal distribution of the KSSW near the submarine canyon is clear, it is very useful to predict the amount of jellyfish ephyrae and mass occurrences of jellyfish in the future. The goal of this project is very clear and it properly matches the national concerns of the ecosystem. This study is also have important economic value due to the influence of jellyfish bloom to the fishery.

黄海西侧水域近年来水母灾害旺发，研究表明长江口外水下河谷偏北的底层水域是水母碟状体的重要繁殖地，每年5-6月份碟状体最先在该海域出现，而温度和盐度对水母碟状体萌发具有重要影响。另一方面研究表明，黑潮次表层水可以入侵到长江口外的水下河谷区域，由于其起源于台湾东部黑潮水的100-300米层，其水温、盐度、营养盐和溶解氧浓度，都与近岸水的性质显著不同。在春季，黑潮次表层水入侵到长江口外水下河谷区域后，由于其高温、高盐特征，从而对水母繁殖区具有重要影响，然而控制黑潮次表层水在该区域出现的动力机制和其去向目前是不清楚的？因此开展黑潮次表层水向北越过长江口外水下河谷的动力机制及去向研究，阐明影响黑潮次表层水越过河谷向北入侵的动力过程和机制，明确黑潮次表层水在河谷处的空间和时间分布特征，对研究和预测水母碟状体的数量以及未来几个月水母灾害趋势具有非常明确而迫切的国家需求和重要的科学和经济价值。

在本项目资助下，基于数值模式和观测资料，对影响台湾以东黑潮次表层水进入长江口外水下河谷的动力机制进行了研究，分析了入侵水对生态环境的影响，发表国际一流SCI论文12篇，建成了海洋动力环境的预报系统和物理生态耦合模式，培养博士研究生3名，出站博士后2名。(a)基于ROMS模式四维变分同化方法，建成了东中国海海洋动力环境四维变分同化预报系统，并实现了业务化运行（访问地址：https://4dvars.apps.iocasdata.com/），相关成果发表在数值模拟领域的顶级期刊“Ocean Modelling”上。（b）基于数值模式，分析了驱动东海陆架环流形成的主要动力机制，通过动力诊断、数值试验和理论分析，发现东海陆架环流主要由太平洋的风应力旋度所确定，指出近海环流主要由于大尺度的大洋环流所决定，相关成果发表在JGR-Oceans和Continental Shelf Research上。（c）为研究台风对黑潮次表层水向近海入侵的影响，建立了高分辨的物理-生态耦合模式，模式构建工作发表在JGR-Biogeoscience上。(d)并用模式复现了台风“灿鸿”过境期间的生态响应及物理过程，研究发现由底层入侵到东海陆架内部的黑潮次表层水在台风期间能够涌升到上层，为后续的浮游植物爆发提供了丰富的磷酸盐。通过三维动量诊断，研究发现台风“灿鸿”激发了三类上升流：风致埃克曼抽吸、波动抽吸、过境后的涡致抽吸。台风不仅激发与开阔大洋中相似的、沿路径演变的近惯性波动响应，还能够在陆架区激发沿岸传播的陆架波，是沿岸海域独特的响应特征。台风过境后一段时间内，持续存在的涡旋场能够源源不断地向上层海洋输送营养物质。台风促使富含营养盐的黑潮次表层水到达表层，奠定了藻华爆发的营养盐基础。（e）揭示了气旋和反气旋涡旋撞击黑潮主轴对跨陆架磷酸盐通量的不同影响，利用伴随模式揭示了，黑潮次表层水的对浙江外海赤潮的影响，指出北纬30°N以南的高叶绿素主要由黑潮入侵水控制，相关成果发表在Front. Mar. Sci.和JGR-Biogeoscience上。研究成果表明深海大洋对近海生态环境变化具有重要影响，开发的耦合模式和预报系统具有重要的科学意义和应用价值。