Table_10_Seasonal dynamics of major phytoplankton functional types in the coastal waters of the west coast of Canada derived from OLCI Sentinel 3A.docx

Monitoring the spatial distribution and seasonal dynamics of phytoplankton functional types (PFTs) in coastal oceans is essential for understanding fisheries production, changes in water quality, and carbon export to the deep ocean. The launch of new generation ocean color sensors such as OLCI (Ocean Land Color Instrument) onboard Sentinel 3A provides an unprecedented opportunity to study the surface dynamics of PFTs at high spatial (300 m) and temporal (daily) resolution. Here we characterize the seasonal dynamics of the major PFTs over the surface waters of the west coast of Canada using OLCI imagery and Chemical Taxonomy (CHEMTAX, v1.95) software. The satellite-based approach was adapted from a previously proven Empirical Orthogonal Function (EOF)-based algorithm by using a local matchup dataset comprising CHEMTAX model output and EOF scores derived from OLCI remote sensing reflectance. The algorithm was developed for the following PFTs: diatoms, dinoflagellates, dictyochophytes, haptophytes, green algae, cryptophytes, cyanobacteria, raphidophytes, and total chlorophyll-a (TChla) concentration. Of these PFTs, first level evaluation of the OLCI-derived retrievals showed reliable performance for diatoms and raphidophytes. The second level of validation showed that TChla had the best performance, and green algae, cryptophytes, and diatoms followed seasonal trends of a high temporal resolution in situ CHEMTAX time-series. Somewhat reduced correspondence was observed for raphidophytes. Due to their low contribution to the phytoplankton community (26%) and low range of variation, weak performance was noted for haptophytes, dictyochophytes, cyanobacteria, and dinoflagellates. The EOF-based PFT maps from daily OLCI imagery showed seasonal spring and fall diatom blooms with succession from spring blooms to high diversity flagellate dominated summer conditions. Furthermore, strong localized summer raphidophyte blooms (Heterosigma akashiwo) were observed, which are a regionally important harmful species. Overall, this study demonstrates the potential of the OLCI in deriving the surface dynamics of major PFTs of the Strait of Georgia (SoG), a critical habitat for the juvenile Pacific Salmon.

监测沿海海域浮游植物功能类群（phytoplankton functional types, PFTs）的空间分布与季节动态，对于理解渔业生产力、水质变化以及向深海的碳输出至关重要。搭载于哨兵3A（Sentinel 3A）卫星的新一代海洋水色传感器——海洋陆地颜色传感器（Ocean Land Color Instrument, OLCI）的发射，为开展高空间分辨率（300米）、高时间分辨率（逐日）的PFT表层动态研究提供了前所未有的契机。本研究利用OLCI影像与化学分类法软件（Chemical Taxonomy, CHEMTAX, v1.95），刻画了加拿大西海岸表层海域主要PFTs的季节动态。该卫星反演方法借鉴了此前已验证的基于经验正交函数（Empirical Orthogonal Function, EOF）的算法，通过构建包含CHEMTAX模型输出结果与OLCI遥感反射率衍生EOF得分的局地匹配数据集。本算法针对以下PFTs开发：硅藻、甲藻、网藻（dictyochophytes）、定鞭藻（haptophytes）、绿藻、隐藻、蓝细菌、针胞藻（raphidophytes）以及总叶绿素-a（total chlorophyll-a, TChla）浓度。对OLCI反演结果的一级评估显示，硅藻与针胞藻的反演性能可靠。二级验证结果表明，TChla的反演效果最佳，绿藻、隐藻与硅藻的反演结果与原位CHEMTAX时间序列的高分辨率季节变化趋势相符。针胞藻的对应性略有下降。鉴于定鞭藻、网藻、蓝细菌与甲藻在浮游植物群落中的占比低（26%）且变化幅度小，其反演性能较弱。基于逐日OLCI影像得到的EOF反演PFT分布图，显示出春季与秋季的硅藻藻华，并呈现出从春季藻华向以高多样性鞭毛藻主导的夏季群落的演替过程。此外，研究还观测到局地性的夏季针胞藻藻华（即赤潮异弯藻Heterosigma akashiwo），该物种是该区域重要的有害藻华物种。总体而言，本研究证明了OLCI传感器可用于反演乔治亚海峡（Strait of Georgia, SoG）表层海域主要PFTs的动态变化，而乔治亚海峡是太平洋鲑幼鱼的关键栖息地。