Applicability assessment for global standard algorithm of marine primary production in the seas surrounding Taiwan around the Tropic of Cancer in the northwest Pacific

The Vertically Generalized Production Model (VGPM) is a standard algorithm of satellite-derived primary production which is widely used to study the effect of climate change on marine ecosystem, but whether it can be accurately applied to regional seas remain questionable. Taiwan is an island and its central is located near the Tropic of Cancer (23.5 °N) in the northwest Pacific. The sea surrounding Taiwan is rich in biological resources and biodiversity due to the rugged seabed topography and the fluctuation of three major water masses (Kuroshio, South China Sea and China Coastal Water). In order to study the effect of climate change on marine ecosystem in the sea surrounding Taiwan and assess the applicability of VGPM, seasonal field investigations of primary production were conducted in 2018. Seasonal variation of primary production observed in winter, spring, summer and autumn is between 42-911, 113-456, 124-832, 249-1898 mgC m^-2 d^-1, respectively. The corresponding sea surface temperature variations were 15.9-25.7, 23.5-28.4, 28.5-30.4 and 21.7-26.5 °C, respectively. Comparing the measured data with the VGPM model results (measured values of sea surface chlorophyll concentration, euphotic zoon depth, day length and light intensity were used in the model), the average relative error of measured and model results are 466±321, 318±252, 4±48 and 98±61 % in winter, spring, summer and autumn, respectively. The high relative error mainly comes from the inaccuracy of the temperature-dependent optimal carbon fixation rate $\left( {P_{opt}^B} \right)$, which is the most important factor affecting the accuracy of the model. Our results show that primary production derived from the VGPM model cannot be used for long-term research on climate change in the seas surrounding Taiwan.