【作者】 刘洋；

【导师】 吴德星； 鲍献文；

【作者基本信息】 中国海洋大学 ， 物理海洋， 2010， 博士

【摘要】 南海是北太平洋最大的边缘海,其特殊的地理位置和复杂的水深地形,使得内部水体在固有性质、运动方式和规律等方面兼有大洋和浅海双重特征,历来为海洋学者所关注。其中,南海的次表层、中层水团是水体垂向结构中两个特征最明显的水团,其物理化学性质、环流结构均为构成南海水体环境的重要部分。本文在收集、整理南海海区多年实际观测水文资料的基础上,融合Argo浮标观测数据、海表高度异常和蒸发降雨等再分析资料,从传统水团分析的温、盐要素出发,结合溶解氧、营养盐等化学要素,对南海水体的垂直结构和次表层、中层水团核心深度上的各要素水平空间分布情况加以阐述,分析相应层次上的水体运动特征。通过探讨气候态各要素的季节变化规律,重新给出了统计意义下的南海次表层、中层流场结构。文中首次将溶解氧含量纳入到南海水团的物理海洋研究中,追踪特征水体。其与垂向次表层、中层水团有着较好的对应关系,并且在等值线分布趋势中比温度、盐度变化具有更高的分辨率。在垂直方向上,与北太平洋水垂直分布类似,南海内部水体的温-盐关系总体上呈现反“S”结构,即在次表层水、中层水的核心深度上存在盐度极大值、极小值现象。溶解氧含量在垂直方向上形成与盐度相似的相对稳定的极值结构,即对应于水团结构其垂向上存在极大值和极小值,分别对应了次表层水的上界和中层水的下部。营养盐在垂向上表现出随深度加深,含量增大的特征,在达到极值后其量值随深度增加则几乎不变,营养盐的垂向季节变化不明显。黑潮入侵和南海内部水体性质在次表层的季节性变化充分反映了该层水体运动特征。统计结果显示,南海内部的次表层水体特征对南海冬季季风有着积极地响应。黑潮水在次表层主要是由吕宋海峡北部进入,沿西部陆坡向南海南部扩展,而不是按黑潮“流套”理论所示,于海峡处南进北出的路径行进；黑潮入侵在冬、夏季较强,春、秋季较弱。南海溶解氧含量终年呈现出吕宋海峡以东高于南海内部,南海内部以东南海区为低值中心的规律；营养盐含量在该水层上的分布与溶解氧截然相反,始终保持南海内部营养盐含量高于吕宋海峡以东的黑潮区,南海南部高于北部的规律,但其分布表明的水体运动态势却与溶解氧的保持基本一致。通过分析南海中层水核心层上多种要素的水平分布,着重以溶解氧、硝酸盐含量作为判别指标,发现中层水仍具有季节变化特征,且吕宋海峡中北部的水交换较之次表层更为复杂,导致这种变化的主要机制是海面风场引发的一种连续水体间的补偿性效应。中层水营养盐含量的分布格局总体与次表层水相同,依然是吕宋海峡以东的含量较低,南海内部含量相对较高,季节变化不明显。此外,本文还讨论了南海气候态年平均以及季节平均的地转流场特征,从动力学角度解释形成各要素分布结构的原因。次表层及中层流场也都具有季节变化特征,冬季南海北部二者均为气旋式环流,而夏季的次表层流场则出现偶极子结构,该结构具有约半年的时间尺度特征。结合海表面高度异常的分布,确定南海中稳定存在的两个次海盆环流分别位于吕宋岛西侧海域、越南东部外海,其时间尺度均为一个季度左右,空间尺度可达几百公里。最后,本文尝试将FFM (Freshwater Fraction Method)方法应用在南海与北太平洋水交换量的计算工作中,利用保守要素盐度的差异和稳定地淡水注入量估算了吕宋海峡处年平均水体交换量,结果显示吕宋海峡上400m层是水交换活跃区,水平对流在水交换过程中占据主导地位。更多还原

【Abstract】 The South China Sea (SCS) is the largest marginal sea in the North Pacific Ocean. Since its unique geographic location and the varied topography, the SCS shows its particularities in the aspects of water inherent features, the way and the pattern of motions. All of these attract the oceanographers. The subsurface and intermediate water masses of the SCS take on prominent characteristics in the vertical. The whole environment in the SCS is influenced by the distributions and variations of physical and chemical properties and also by the circulation pattern.Based on collecting and processing the historical cruise data, a climatological dataset of the hydrographic elements is accomplished in this thesis. Combined with the Argo float data, sea level anomaly, evaporation and precipitation reanalysis data, the seasonal and regional variations of the elements are discussed in this thesis, mainly focusing on the vertical and horizontal distribution for temperature, salinity, dissolved oxygen (DO) and nutrients (including nitrate, phosphate and silicate). At last, it is given of an updated circulation structures on the core depths of subsurface and intermediate water masses in the statistical sense.In the study of analysis of the SCS water masses, it is the first time to apply dissolved oxygen data to trace typical water body. There is a better relation between the DO concentration and the water masses than that between either temperature or salinity and the water masses in the deep sea. Moreover, DO concentration has a much higher resolution in the deeper layers.T-S curves showed a reversed "S" vertical structure for the water near the east of Luzon Strait (LS) and the inner SCS. The salinity reached its maximum and minimum value at the core layers of subsurface and intermediate waters respectively. It is similar to the vertical structure of dissolved oxygen. The DO maximum and minimum values corresponded well to the upper boundary of subsurface water and lower part of intermediate water. The nutrients first showed an increasing trend from the surface down to a certain depth and then kept steady in the abyss, and there were no clear seasonal variations in the distribution of nutrients.On the subsurface water level, the kinetic mechanism could be figured out in the seasonal variations of Kuroshio intrusion and hydrologic elements. The statistic results in this thesis show that the intrusion mainly occurred at the north of the LS and extending to the south of the SCS along the continental slope in the west. The intrusion path is different from the way mentioned in hypothesis of "loop current" in which it was believed that the Kuroshio branch came to the SCS through the south end of the LS and turned back through the north. It was also shown that the intrusion depended on the SCS monsoon. In winter and summer, it was strong and turned weak in spring and autumn. It also keeps the balance with the water near the west of Palawan Island which is characterized by the low temperature, low salinity and low dissolved oxygen. The characteristics of subsurface water could respond to the winter monsoon rapidly. The distributions of dissolved oxygen and nutrients content follow the regulations:DO concentration is higher in the Kuroshio Current region and lower in the SCS; the low concentration core in the SCS occurrs at the southeast. Additionally, the distribution of nutrients are opposite to DO, i.e. it is higher in the SCS than the North Pacific, and it is higher at the south than the north in the SCS, but this opposite distribution could reflect the same water movement trends.Based on the multi-elements analysis on the core level of the intermediate water, the results show that a seasonal variation for DO distribution exists. The water exchange through the middle and north part of the LS is more complex than that in the subsurface water. A kind of compensatory effect in the continuous water body is the main mechanism which can cause the seasonal phenomenon. The nutrients concentrations in the intermediate water have the same regional structures with the subsurface water, but the difference is that there is no obviously seasonal variation for them.Furthermore, the thesis also discusses the annual mean and seasonal mean geostrophic current under the sign of climatology and gives the dynamical mechanism for the distributions. There are the basin-scale cyclonic circulations on the core level of subsurface and intermediate water masses and the circulations change in the north of the SCS during winter monsoon. The dipole shows during summer and it has the half-year time scale characteristic in the south of the SCS. Considering the sea level anomaly simultaneously, two subbasin-scale phenomenoa exist in the west of Luzon Island and offshore region in the north of Vietnam. The time scale is about one season and the spatial scale is about several hundred kilometers.The Freshwater Fraction Method is applied to calculate the flushing time and water transport between the SCS and the North Pacific Ocean. The conservation of salt in the sea water, the salinity difference between east and west of the LS and the steady volume of freshwater input are the key points for this experiment. From the results, most of the water exchange occurs on the upper 400m, the advection dominates over diffusion in the water exchange through the LS.更多还原