Zhang Hailong, Devred Emmanuel, Fujiwara Amane, Qiu Zhongfeng, Liu Xiaohan
Opt Express. 2018 Nov 26;26(24):32280-32301. doi: 10.1364/OE.26.032280.
Knowledge on the phenology and distribution of phytoplankton taxonomic groups (PTGs) represent valuable information when studying marine ecosystem, especially in the Arctic Ocean where rapid warming has drastic effects on sea-ice dynamics, which affect the marine food web. Taxonomic groups of phytoplankton can be discriminated based on their pigment signatures, which, in turn, impact their absorption spectra, given that different pigments have different absorption windows in the visible. Using concurrent measurements of phytoplankton diagnostic pigments and absorption spectra (a) collected in the Bering and Chukchi Seas, a novel and direct approach was designed for simultaneously estimating the biomass concentrations of several PTGs (Ci) as well as their specific absorption coefficient. The chemotaxonomic tool CHEMTAX was applied to twelve diagnostic pigments measured by high-performance liquid chromatography (HPLC). Their results revealed that the phytoplankton community composition was made of nine groups, from which six dominant were identified: diatoms, dinoflagellates, c3-flagellate, haptophytes type 7, two types of prasinophytes. Out of 117 samples, twenty pairs of Ci derived by CHEMTAX and measured a were randomly selected and used in a linear unmixing model to extract the specific absorption spectral of each group. This step was repeated 1000 times to provide the mean specific absorption of a given phytoplankton group. These specific absorption spectra were used to reconstruct total a, which was consistent with the measured a (R from 0.8 to 0.95) at all visible wavelengths (400-700 nm). The derived specific absorption spectra were further used with the measured a(λ) at ten Moderate Resolution Imaging Spectroradiometer (MODIS) wavebands in a linear unmixing model to test the ability to retrieve the concentrations of PTGs from satellite remote sensing. A comparison between estimated and measured Ci showed that the approach used in this study performed best when retrieving five groups (i.e., dinoflagellates, c3-flagellate, haptophytes, two types of prasinophytes) from the nine initially identified using CHEMTAX with a mean absolute percentage error (MAPE) <35%, except for diatoms with a MAPE value of about 45%. Our approach provides a practical basis for estimation of PTGs using a(λ) derived from satellite observations and field measurements.
在研究海洋生态系统时，了解浮游植物分类群（PTG）的物候和分布情况具有重要价值，尤其是在北冰洋，那里的快速变暖对海冰动态产生了巨大影响，进而影响了海洋食物网。浮游植物的分类群可以根据其色素特征来区分，鉴于不同色素在可见光范围内有不同的吸收窗口，这些色素特征反过来又会影响它们的吸收光谱。利用在白令海和楚科奇海同时进行的浮游植物诊断色素和吸收光谱（a）测量，设计了一种新颖的直接方法，用于同时估算几种PTG（Ci）的生物量浓度及其特定吸收系数。将化学分类工具CHEMTAX应用于通过高效液相色谱（HPLC）测量的12种诊断色素。结果表明，浮游植物群落组成由9个类群组成，其中确定了6个优势类群：硅藻、甲藻、c3鞭毛虫、7型定鞭藻、两种绿藻。在117个样本中，随机选择20对由CHEMTAX得出的Ci和测量的a，并将其用于线性混合模型中，以提取每个类群的特定吸收光谱。这一步骤重复1000次，以提供给定浮游植物类群的平均特定吸收。这些特定吸收光谱用于重建总a，在所有可见光波长（400 - 700 nm）下，总a与测量的a一致（R为0.8至0.95）。得出的特定吸收光谱进一步与在十个中分辨率成像光谱仪（MODIS）波段测量的a(λ)一起用于线性混合模型，以测试从卫星遥感中检索PTG浓度的能力。估计的Ci与测量的Ci之间的比较表明，本研究中使用的方法在从最初使用CHEMTAX识别出的9个类群中检索5个类群（即甲藻、c3鞭毛虫、定鞭藻、两种绿藻）时表现最佳，平均绝对百分比误差（MAPE）<35%，除了硅藻，其MAPE值约为45%。我们的方法为利用卫星观测和实地测量得出的a(λ)估算PTG提供了实际依据。
