Two-decadal estimation of sixteen phytoplankton pigments from satellite observations in coastal waters

Abstract

Knowledge of the marine phytoplankton communities is vital for understanding the carbon cycle, ecological and biogeochemical processes, and climate change. Phytoplankton assemblages contain multiple pigments that play a significant role in describing the phytoplankton communities. Thus, detecting the concentrations of phytoplankton pigments is of great significance. Here, an extensive in situ observation dataset, including the phytoplankton absorption coefficient, concentrations of phytoplankton pigments, and remote sensing reflectance, was collected during seven cruise surveys in the Bohai Sea, Yellow Sea, and East China Sea. This study developed a customized absorption-based remote sensing model using the Gaussian decomposition technique, which closely links phytoplankton absorption characteristics with various pigments. This model was repeatedly assessed to guarantee its stable performance, and was evaluated using the in situ observation dataset and the leave-one-out cross-validation method, yielding results of competitive and acceptable errors (e.g., mean absolute percentage errors (MAPEs) below ∼60% for most pigments). Satellite match-up validation also generated promising predictive errors, with the derived MAPEs in a ∼10%–40% range for most pigments. Another contribution of our study is the application of the developed model to a long time series of satellite data (1998–2019), and the 22-year data record that documents the spatiotemporal variation of 16 pigment concentrations in the study areas. Accordingly, the long-term spatial and temporal evolution rules of 16 pigments are reported for the first time. This work concludes that the pigments (as the second-order delegates of phytoplankton pigments, compared to chlorophyll-a) can be retrieved from satellite data, despite the presence of optically complex turbid coastal waters, thus providing refined characteristics on phytoplankton assemblages for future marine research.