Journal of Tropical Oceanography >
Particle backscattering as a function of chlorophyll a concentration off the eastern Hainan coast in the South China Sea*
Copy editor: LIN Qiang
Received date: 2021-09-10
Revised date: 2021-10-18
Online published: 2021-10-20
Supported by
Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering, Guangdong Laboratory (Guangzhou)(GML2019ZD0602)
Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering, Guangdong Laboratory (Guangzhou)(GML2019ZD0305)
National Natural Science Foundation of China(41976172)
National Natural Science Foundation of China(41976170)
National Natural Science Foundation of China(41976181)
National Natural Science Foundation of China(41576030)
National Natural Science Foundation of China(41776044)
National Natural Science Foundation of China(41776045)
Science and Technology Planning Project of Guangzhou(201707020023)
State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences(LTOZZ2003)
Variability of light backscattering coefficient in the ocean can be used to quantify the biomass of phytoplankton, which can be applied in remote sensing and optical profile observation platforms to obtain the characteristics of phytoplankton biomass spanning various spatio-temporal scales and vertical profiles in the ocean. Significant variabilities of the bio-optical properties exist off the eastern Hainan coast, being influenced by upwelling. Based on the in-situ data collected off this area in 2013, we established a regional algorithm between the backscattering coefficient of particle [bbp] and chlorophyll a concentration [Chl a]. The algorithm is based on the assumption that the particle backscattering coefficient is determined by the constant background backscattering value independent of Chl a and two components by pico (< 2 μm) and large(>2 μm)phytoplankton. Results show that the modelled bbp values agree well with measurements, especially for low Chl a concentration. The relationships between bbp and Chl a vary in different water layers. For example, the constant background backscattering values at the bottom layer are significantly higher than those in the upper layer, indicating that driven by upwelling, the increasing concentration of submicron particles not covariant with Chl a might produce an increasing backscattering coefficient. At the chlorophyll maximum layer, the background backscattering values are significantly lower than those in the upper water, and the contribution percentage of background backscattering value is about 21%~35%. With the increase of Chl a concentration, the contribution of large phytoplankton to bbp increases significantly, accounting for 50% or higher, while the contribution of pico phytoplankton remains stable around 40%. Understanding the regional relationship of bbp and Chl a off the eastern Hainan coast can improve our understanding of marine biogeochemical processes in the region.
ZHOU Wen , WEI Panpan , LI Cai , WANG Guifen , ZHENG Wendi , DENG Lin , ZHAO Hongwuyi , YU Linghui , CAO Wenxi . Particle backscattering as a function of chlorophyll a concentration off the eastern Hainan coast in the South China Sea*[J]. Journal of Tropical Oceanography, 2022 , 41(3) : 29 -37 . DOI: 10.11978/2021123
图1 南海琼东海域实验站位图该图基于国家测绘地理信息局地图服务网站下载的审图号为GS(2019)1819号的标准地图制作, 底图无修改 Fig. 1 Locations of stations off the eastern Hainan coast in the South China Sea. This map is made based on the standard map no. GS (2019) 1819 downloaded from http://bzdt.ch.mnr.gov.cn, without modification of the base map |
图2 bbp(490)与Chl a的散点图及模型拟合曲线模型拟合结果标识为黑色实线, 虚线将整个数据集划分为两部分, 实心黑点代表底部雾状层样品; 空心点代表上层水体样品, 灰色区域代表95%置信区间 Fig. 2 Log-log scatter plot of bbp(490) vs. Chl a. The samples are divided into upper and bottom samples by the dotted line. The fitted curves for upper (open circles) and bottom samples (black dots) are given by black solid lines. Gray shading represents a model ensemble calculated by varying model parameters between 95% confident intervals |
表1 模型拟合参数Tab. 1 The fitted parameters of the model |
水层 | 拟合参数 | ||
---|---|---|---|
bbp,p*(490)/(m2·mg-1) | bbp,mn*(490) /(m2·mg-1) | bbp,k(490) /(m-1) | |
上层水体 | 0.0015 | 0.00179 | 0.001161 |
表层水体 | 0.0052 | 0.00560 | 0.000894 |
中层水体 | 0.0051 | 0.00543 | 0.000626 |
叶绿素最大层 | 0.0025 | 0.00288 | 0.000571 |
底层水体 | 0.0563 | 0.05660 | 0.006719 |
图3 上层样品(a)和底层样品(b)各种组分对bbp(490)的贡献百分比与Chl a浓度之间的关系图蓝色区域代表95%置性区间 Fig. 3 Percent contribution of each component population to bbp(490) as a function of Chl a for upper samples (a) and bottom samples (b). Blue shading represents a model ensemble calculated by varying model parameters between 95% confident intervals |
图4 本文构建模型与其他模型拟合结果对比a. 本文模型与幂函数拟合结果; b. 本文模型与其他文献模型结果对比; 实线代表本文构建模型拟合结果, 虚线代表幂函数拟合结果 Fig. 4 Comparison of the fitted relationship in this study to other relationships in publications. (a) Comparison of the fitted curves from the model (black solid line) and from the power function (dotted line ) for two groups; and (b) comparison of the fitted curves from the model (black solid line) and other publications (colored lines) |
图5 分层bbp与Chl a模型拟合图a. 水体表层(黑点)、叶绿素最大层(绿点)及两者之间的中间层(橙点)的分层模型拟合结果; b. 分层模型估算的各组分后向散射对bbp的贡献百分比随Chl a浓度的变化, 颜色代表水层与图(a)一致 Fig. 5 Relationships between bbp and Chl a for different water layers. (a) The fitted curves for surface samples (black dots), chlorophyll a maximum layer samples (green dots), and others (orange dots); and (b) percent contribution of each component population to bbp(490) as a function of Chl a for samples of the three groups |
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