Vertical variability in the bio-optical properties of seawater in the northern South China Sea (NSCS) including inherent optical properties (IOPs) and chlorophyll a concentration (Chl) were studied on the basis of in situ data collected in summer 2008 using an absorption/attenuation spectrophotometer. An empirical model was developed to estimate Chl profiles based on the absorption line height at long wavelengths, with a relative root mean square error of 37.03%. Bio-optical properties exhibited large horizontal and vertical spatial variability. As influenced by coastal upwelling and the Zhujiang River (Pearl River) discharge, both IOPs and Chl exhibited high values in the surface waters of the inner shelf, which tended to decrease with distance offshore. Subsurface maximum layers of IOPs and Chl were observed in the middle and outer shelf regions, along with significantly higher values of attenuation coefficients beneath this layer that rapidly increased towards the bottom. In the open ocean, both IOPs and Chl exhibited consistent variability, with the subsurface maximum layer typically located at 34–84 m. Phytoplankton were found to be one of the major components in determining the vertical variability of bio-optical properties, with their vertical dynamics influenced by both physical forcing and light attenuation effects. The depth of the subsurface maximum layer was found to be closely related to the fluctuation of the oceanic thermocline and the depth of the euphotic zone, which also affected the total integrated biomass of the upper ocean. Typically high values of attenuation coefficients observed in the bottom waters of the continental shelf reflected the transport of particulate matter over the bottom boundary layer. Our results reveal large spatial differences in bio-optical profiles in response to complex marine ecodynamics in the NSCS. From the perspective of marine research, high-resolution optical measurements are clearly advantageous over conventional bottle sampling.

中文翻译：

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2008年夏季南海北部海水生物光学特性的垂直变化

根据2008年夏季使用吸收/吸收法收集的原位数据，研究了南海北部海水（NSCS）的海水生物光学特性的垂直变化，包括固有光学特性（IOP）和叶绿素a浓度（Chl）。衰减分光光度计。建立了一个经验模型来根据长波长处的吸收线高度估算Chl谱，相对均方根误差为37.03％。生物光学特性表现出较大的水平和垂直空间变异性。受沿海上升流和珠江（珠江）流量的影响，IOP和Chl内陆表层水表现出较高的价值，并随着离岸距离的增加而降低。在中层和外层架子区域观察到了IOP和Chl的地下最大层，并且在该层下的衰减系数值明显更高，并朝着底部迅速增加。在公海中，IOP和Chl表现出一致的可变性，地下最大层通常位于34–84 m。发现浮游植物是确定生物光学特性的垂直变化的主要成分之一，其垂直动力学受物理强迫和光衰减效应的影响。发现地下最大层的深度与海洋温跃层的波动和富营养区的深度密切相关，这也影响了上层海洋的总生物量。通常，在大陆架底部水域中观察到的高衰减系数值反映了颗粒物质在底部边界层上的传输。我们的结果表明，响应于NSCS中复杂的海洋生态动力学，生物光学剖面的空间差异很大。