海洋环流与波动重点实验室知识库

黑潮次表层水的入侵是黑潮与中国东海进行水体和物质交换的重要途径之一。然而，迄今为止黑潮次表层水在东海陆架底层向浙江近海区域运动的动力机制和关键影响因素尚不清楚，大洋和长江输入的营养盐对长江口及其邻近海域浮游植物生长的贡献也没有比较统一的认识。

本文基于ROMS（Regional Ocean Model System）建立了东海高分辨率的三维海洋动力模式，结合示踪物和观测资料，研究了黑潮次表层水入侵浙江近海的时空变化、动力机制以及影响入侵程度的主要因素。模拟结果很好地再现了东海海域温度、盐度和流场的基本特征与季节变化。观测与模拟的温度和盐度均表明黑潮次表层水向浙江近海的入侵存在六月份强、十二月份弱的季节变化。在台湾以东释放示踪物追踪黑潮次表层水的运动，示踪结果也证明了黑潮次表层水向浙江近海的入侵存在夏季强、秋冬弱的季节变化。此外，示踪物浓度随时间的变化还表明台湾以东的黑潮次表层水至少需要约1.5个月才能到达浙江近海区域。动量分析的结果表明黑潮次表层水从台湾东北到浙江以南海域的北向运动主要受压强梯度的影响，而在浙江近海附近的向岸运动主要是底Ekman作用的结果。压强梯度和底摩擦力的季节变化使得黑潮次表层水在六月能够跨过60m等深线入侵到浙江近海区域而在十二月则不能。敏感性试验表明黑潮次表层水对浙江近海夏季增强、冬季减弱的入侵变化主要是由夏季和冬季风应力的变化引起的。同时，试验还表明西南季风增强、台湾暖流的温度升高或者流速减弱、台湾以东黑潮的温度降低或者流速变强都有利于黑潮次表层水向浙江近海的入侵，反之，则不利于黑潮次表层水的入侵。

基于ROMS动力学模式与CoSiNE（Carbon, Silicate and Nitrogen Ecosystem）生态模型建立了中国东海海域的生态动力学耦合模式，分析评估了长江和大洋输入的营养盐对长江口及其邻近海域夏季浮游植物生长与分布的相对重要性。耦合模式成功地模拟出了研究区域内的水动力和生物地球化学特征。观测与模拟结果均表明长江口及其邻近海域存在两个叶绿素高值区，分别位于舟山群岛以北的长江口附近和舟山群岛以南的浙江近海区域。数值试验表明北部区域的叶绿素高值主要受长江输入的营养盐控制，而南部区域的叶绿素高值主要受来自大洋的营养盐控制。大洋主要通过来自台湾海峡的台湾暖流和台湾以东的黑潮两个途径向东海陆架输送水体和物质，黑潮输入的营养盐，特别是磷酸盐，对于南部区域叶绿素高值的产生具有最重要的贡献，而台湾暖流输入的营养盐对长江口及其邻近海域叶绿素的贡献较小。研究区域内的水动力和营养盐分布特征也表明黑潮次表层水携带而来的磷酸盐是导致长江口及其邻近海域南部区域发生赤潮最关键的营养盐。

The Kuroshio subsurface water intrusion is an important pathway for the water and material exchanges between the Kuroshio Current and the East China Sea continental shelf. However, the key dynamical mechanism and influencing factors driving the Kuroshio subsurface water to reach as far as the Zhejiang coastal area remain unclear. Moreover, there is no consensus on the relative contributions of the oceanic nutrients and riverine nutrients input from the Changjiang River.

A high-resolution three-dimensional hydrodynamic model is established based on ROMS (Regional Ocean Model System) model in the East China Sea. The model results, passive tracer, and observations are used to study the spatial and tempal variations, dynamical mechanisms, and influencing factors of the Kuroshio subsurface water intrusion to the Zhejiang coastal area. The model well reproduces the seasonal variations of temperature and salinity characteristics and the current structure over the East China Sea continental shelf. The observed and simulated temperature and salinity distributions suggest a seasonal variation of the Kuroshio subsurface water intrusion into the coastal region off the Zhejiang Province of China, which is stronger in June and weaker in December. A passive tracer in the subsurface layer is used to investigate the movement of the Kuroshio subsurface water. Tracer experiments confirm the seasonal variation of the Kuroshio subsurface water intrusion, showing that the intrusion is stronger in summer and weaker in autumn and winter. Moreover, tracer concentrations suggest that in general it takes at least 1.5 months for the Kuroshio subsurface water from east of Taiwan to reach the Zhejiang coastal area. Analyses of the momentum balances indicate that the Kuroshio subsurface water’s northward movement is regulated by the geostrophic current, while the shoreward intrusion results from the bottom Ekman effect. The seasonal changes in pressure gradients and bottom frictions contribute to the Kuroshio subsurface water intrusion into the Zhejiang coastal area in June rather than in December. Sensitivity experiments show that the seasonal variation of the Kuroshio subsurface water intrusion is mainly induced by the different wind stresses in summer and winter. It is also indicated that the Kuroshio subsurface water intrusion would be intensified when there is the stronger southerly monsoon, the weaker and warmer Taiwan Warm Current, or the stronger and colder Kuroshio Current; otherwise the intrusion would be weakened.

A coupled physical-biogeochemical model ROMS-CoSiNE (Carbon, Silicate and Nitrogen Ecosystem) is established to assess the relative importance of riverine nutrients input from the Changjiang River and the oceanic nutrients to the development and distribution of summer phytoplankton blooms in the Changjiang Estuary and the adjacent sea area. The coupled model successfully reproduces the main hydrographic and biogeochemical features of the region. Both satellite observations and model results show two high-chlorophyll regions in the study domain, located around the Changjiang Estuary north of the Zhoushan Islands and in the Zhejiang coastal area south of the Zhoushan Islands, respectively. Numerical experiments show that harmful algal blooms in the region north of the Zhoushan Islands are mainly driven by riverine nutrients from the Changjiang River, while algal blooms in the region south of the Zhoushan Islands are mainly controlled by oceanic nutrients. The oceanic nutrients input into the ECS via two pathways separated by the Taiwan Island, the Taiwan Warm Current and the Kuroshio Current. Nutrients inputs, particularly phosphate, from the Kuroshio Current play the major role in the high chlorophyll concentration in the southern region, while the nutrients from Taiwan Warm Current have little influence on the chlorophyll concentrations in the study region. The distributions of the hydrological condition and nutrients in the Kuroshio Current also indicate that the PO₄ from the Kuroshio subsurface water is the most important nutrient to the high chlorophyll in the southern region of the Changjiang estuary and its adjacent area.