物理过程对东海陆架海域底层水体缺氧时空演变的影响

The Eastern China is one of the most active and productive shelf regions in the world in the aspect of economy. One of the most attractive features of this area in recent decades is the area of severe hypoxia that recurs off the Changjiang (Yangtze) River Estuary (CRE) annually during summer. The CRE has historically experienced low-oxygen events in the near bottom layers as reported fifty years before. Recently, the extent of the so called "dead zone" has increased dramatically since 1999 (or even earlier), likely owing to excessive nutrients inputs from the Changjiang River (CR) or the Kuroshio intrusion water. Now, the size of hypoxic zone is one of the largest in the world. Comparing with worsening trends of hypoxic zones, however, our knowledge is rather poor about the cause, variability and consequence of them..Although it is accepted that hypoxia is driven both by biological processes and physical factors, this proposal is intended to suggest the research priorities and concentrations on the hydrodynamic mechanism related to hypoxia variability. The distribution of hypoxic zone shows a significant event scale, seasonal and inter-annual variability that is probably owing to the physical factors such as changes in the circulation pattern and vertical mixing. This project will directly address several of the program goals including: .(1) Building upon a previous funded and proven realistic full-forcing driven hydrodynamic model in the East China Sea to resolve the dominant hydrographic processes that probably control the timing, duration, and severity of hypoxia of the region, such as the diluted water mass variations. The variability of the Taiwan Warm Current is also taken into considerations due to its invasion into the river valley outside of the CR in summer. .(2) Improving our understanding of the exchange rate and the transport process of nutrients and low oxygen water among the marginal sea. .(3) Developing an ecosystem model by coupling a full 3D hydrodynamic model with various simple oxygen respiration models, which is suitable to the local conditions to predict the primary production and dissolved oxygen in different time scales.?These oxygen respiration models?are also expected to help us to separate the respective contributions to the hypoxia from bio-chemical processes and physical processes.

近海生态系统是承载资源环境压力的重要地带。近年来，人类活动加剧了近海富营养化程度，使底层水体缺氧现象发生的频率升高、范围更广、持续时间更长，从而可能给近海生态环境带来潜在的危害或变化。东海陆架海域是全球缺氧现象最为严重的海域之一。该海域的缺氧现象呈现多种时间尺度与较大空间尺度的变化，复杂多变的环流系统和丰富的营养盐来源是缺氧时空结构多变的主要因素之一。本项目主要从物理过程出发，基于大量的现场多学科资料和锚系平台的连续剖面观测资料，利用水动力数值模拟并结合简化的生态过程模式，研究层化演变过程及其主要因素，查明几种平流过程和不同来源的营养盐输运对本海域富营养化的影响程度，定量研究溶解氧的垂向和水平交换速率，平流过程对缺氧水团演变的影响。在此基础上，揭示东海陆架海域物理过程对缺氧的形成与演变的作用。本研究可为建立或完善缺氧的物理-生态耦合模式奠定基础，并为缺氧灾害的预测预警提供科学依据。

缺氧是物理、化学和生物交叉学科的研究内容，是当今世界海洋研究的热点。近几十年来，全球近海缺氧区发现的数量成倍上升，目前已经超过200多个。长江口缺氧无论是面积还是严重性均是其中较为显著的海域。本项目主要从营养盐的不同来源、层化的演变角度出发，研究长江和黑潮对东海缺氧区时空演变的重要影响。东海和黑海跨陆坡交换的比较研究证实了季节和季节间尺度内近海-陆坡交换过程对生态环境演变的重要作用。在东海的研究案例中根据2006年的实际强迫条件模拟得到的跨陆架年平均交换通量为2.6Sv，远远大于多年平均的入侵通量；台湾海峡的年平均北上通量为1.8Sv，也比多年平均的1.5Sv高出20%。提出了2006年缺氧区北移是由于黑潮和台湾海峡入侵增强的假说，有助于在动力上解释2006年长江口缺氧区显著向北移动的机理。在黑海陆架的对比研究中，揭示了涡旋在移动过程中不断与陆坡相互作用，并将外海水携带入陆架，将陆架水携带至外海，引起交换的平均流量约为0.2 Sv，约占整个黑海西北部陆架与深海交换的20%。在物理机制明确的情况下，建立了可用于缺氧形成和演变过程预测的黄东海物理-生态耦合模型。项目负责人晋升为研究员。累计发表科研论文7篇，其中第一作者SCI收录论文4篇，包括2篇JGR-oceans，1篇DSRII，1篇CSR；获得专利4项。项目负责人获得了国家重点研发计划课题和国家自然基金委面上项目的后续支持。