| Wang Guifen,Zhou Wen,Xu Zhantang,Xu Wenlong,Yang Yuezhong,Cao Wenxi. 2020. Vertical variations in the bio-optical properties of seawater in the northern South China Sea during summer 2008. Acta Oceanologica Sinica, 39(4):42－56 |
| Vertical variations in the bio-optical properties of seawater in the northern South China Sea during summer 2008 |
| 2008年夏季南海北部海区生物光学特性的垂向变化特征 |
| Received:January 28, 2019 |
| DOI：10.1007/s13131-020-1535-y |
| Key words:vertical distribution phytoplankton bio-optical properties subsurface maximum layer northern South China Sea |
| 中文关键词: 垂向分布 浮游植物 生物光学特性 次表层叶绿素最大值层 南海北部海区 |
| 基金项目:The National Natural Science Foundation of China under contract Nos 41776045 and 41576030; the Fundamental Research Funds for the Central Universities under contract No. 2017B06714; the Open Project Program of the State Key Laboratory of Tropical Oceanography under contract No. LTOZZ1602; the Science and Technology Program of Guangzhou, China under contract No. 201607020041. |
| Author Name | Affiliation | E-mail | | Wang Guifen | College of Oceanography, Hohai University, Nanjing 210098, China | guifenwang@hhu.edu.cn | | Zhou Wen | State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China | | | Xu Zhantang | State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China | | | Xu Wenlong | College of Oceanography, Hohai University, Nanjing 210098, China | | | Yang Yuezhong | State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China | | | Cao Wenxi | State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China | |
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| Abstract: |
| 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. |
| 中文摘要: |
| 基于2008年夏季在南海北部海区投放的吸收/衰减测量仪观测的高垂向分辨率数据，研究了海水固有光学参数（IOPs，全称Inherent optical properties）和叶绿素浓度（Chl a）的垂向变化特性。基于长波波段海水吸收基线高度建立了反演叶绿素a浓度剖面的经验模型，其相对均方根误差仅为37.03%。生物光学剖面分布表现出明显的空间差异。受沿岸上升流和珠江冲淡水的影响，内陆架表层水体具有较高的IOPs和Chl a，且逐渐向外呈减小趋势；中陆架和外陆架水体存在IOPs和Chl a的次表层极大值现象，且底层水体衰减系数存在典型的高值区；外海水体中IOPs和Chl a的剖面分布表现出一致的次表层极大值特征，最大值层所在深度（ZSCM）约在34m到84m之间。浮游植物是影响研究海区生物光学剖面变化的一个决定性因素，其垂向变化特征受到物理过程驱动和光衰减过程的影响。综合考虑南海北部海区的大部分调查水体，ZSCM与温跃层深度、真光层深度之间存在一致的变化特征，而且与真光层内Chl a浓度积分量相关。底层高衰减系数的分布特征反映出底边界层颗粒物沿陆架底部输运的影响。本文研究结果表明了南海北部海区物理过程驱动下生物光学剖面的响应特征，高垂向分辨率的光学观测相对于传统分层观测表现出明显优势。 |
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