渤海生态系统关键物理生物过程的数值研究

【作者】 刘浩；

【导师】 尹宝树；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 环境科学， 2005， 博士

【摘要】 本文运用数值模型再现了影响渤海生态系统季节变化的关键物理生物过程。就物理过程而言主要进行了两方面内容的研究:一是考察了决定渤海营养盐输运和分布特征的潮汐潮流的状况,潮混合的特征以及潮汐锋的形成机制;二是模拟了河流羽流在渤海的发展过程,以及引潮力和风应力对河流羽流发展的影响。基本成果如下: （1） 渤海的潮汐潮流都是以M₂分潮为主。M₂分潮在秦皇岛以外海域和老黄河口附近各有一个无潮点;其分潮流在沿岸海域及狭窄水道以往复流为主,而在渤海中部,旋转流是其基本运动形式。较为剧烈的地形及岸线变化和浅水区的非线性作用都可导致涨落潮流的非对称性,因此局部涡流成为M₂分潮余流的显著特征。 （2） 渤海深水区的层化结构是海表热通量和垂向混合机制相平衡的结果。春天海表热通量显著增强,层化结构也开始形成,主要分布在潮汐混合较弱的中央水域;夏至时节层化结构无论是发生范围还是层化强度都达到极致;进入秋季,层化强度伴随着海表热通量的减少而削弱,分布区域也逐步向渤海海峡转移;冬季大风进一步增强了海水的垂向混合,此时渤海不再有垂向分层。 （3） 潮汐锋面是海水混合区和层化区的分界面,就水体输送而言,锋面就像一处保留带或动力学意义上的障碍墙,抑制着锋面两侧的水、溶解物和颗粒物质的交换。 （4） 纯浮力作用下河流羽流是一个典型的双层流,密度小的冲淡水浮在密度大的海水上面,在河口附近上层流和下层流流向相反。无论是形成于海底的潮致湍流动能还是生成与海面的风生湍流动能通过垂向扩散都有利于河载物质穿越淡水锋面进行物质交换。 （5） 不同方向的风应力决定了河流羽流的不同发展特征:离岸风有利更多还原

【Abstract】 Numerical models are used to represent key physical-biochemical processes influencing the Bohai ecosystem. In terms of physical process two principal dynamics are stressed in this study: first, features of BS tides and tidal currents which determine the transport and distribution of major nutrients are examined, the character of tidal mixing as well as evolving mechanism of tidal front is also analyzed and discussed with a stratification parameterization fit to shallow shelf-sea; secondly, the river plume development is simulated, and the influence of tide and wind stress on river plume evolution are further examined. Fundamental results are as follows:（1） M₂ constituent is predominant for both tides and tidal currents in BS. There are two amphidromic points for M₂ constituent: one near Qinhuangdao, another close to old Yellow River mouth; rectilinear currents dominate in narrow sea-routes and coastal areas, whereas rotation is the basic moving style in the central BS. Both relatively drastic depth transformation and intense nonlinear interaction of shallow water lead to the asymmetry of ebb/flood tidal current. Therefore, several strong M₂ residual current whorls are evident in BS.（2） Vertical stratification structure comes from the balance between heat flux through sea surface and vertical stirring in the water column. Heat flux increases remarkably in spring, so layering comes into being gradually and concentrates on the central BS where tidal mixing is weak; whether the range or intensity culminates during the Summer Solstice; stratification is weakened in accompany with the decrease of heat flux in the fall, and is still apparent in BS strait; the gale enhances vertical stirring of sea water, so no obvious stratification exists in winter.（3） Tidal front is the interface separating mixing area and stratification area,just like a retention or a dynamic obstacle preventing the exchange of water, particulate or dissoluble material.（4） The pure buoyancy river plume is a typical double-layer flow with light fresh water floating on dense sea water, and different flow direction is evident for the upper and lower current adjacent to estuary. Both tide-induced and wind-forced kinetic dissipation are conducive to weakening fresh water front.（5） Different wind stress determines distinct river plume features: offshore wind enhances seaward development of fresh water inducing strong upwelling in the estuary, whereas shoreward wind confines river discharge to a narrow band along the coast.As one of the important research fruits concerning the dynamic process of BS ecosystem, a NPZD type of biological model, which takes nitrate, ammonium and phosphate as major nutrients and includes another three biological variables -phytoplankton, zooplankton and detritus, is established and coupled with POM, Dobson and Smith irradiance model as well as Vassiliki river discharge model in this study. The biannual blooms of phytoplankton and yearly rise and fall in nutrient contents are successfully reproducing, which is reasonably consistent with true case in BS. In addition, the author also estimates the primary production in every sub-region and completely investigates the BS f-ratio in the first time. By comparison with observed data as well as pioneer work, numerical results presented here are reliable. The model used in this study is especially applicable to water area which has not been subject to eutrophication yet.更多还原