The first data set of seasonal marine environment and euphotic zone integrated primary production (IP) variations in the Taiwan Strait was reported. The measured annual IP was 123 ± 86 gC m −2 year −1 (338 ± 235 mgC m −2 day −1), and its seasonal variations can be described with a left-skewed normal distribution curve. The average seasonal IP values from the highest to the lowest were summer (664 ± 270 mgC m −2 day −1), autumn (350 ± 118 mgC m −2 day −1), spring (202 ± 110 mgC m −2 day −1), and winter (137 ± 68 mgC m −2 day −1). The lowest IP was during the nutrient-rich winter because it had a short insolation duration, low incident photosynthetic active radiation (PAR) and low light transmission (shallow euphotic zone depth) due to strong vertical mixing. In contrast to the winter, the highest IP was during the nutrient-depleted summer, which had a long insolation duration, high incident PAR and high light transmission (deeper euphotic zone depth). In addition, the heterotrophic nutrients from upwelling in the south might also support the highest IP in summer. As three primary water masses exist in the Taiwan Strait and three of them have different characteristics, different mixing ratios of water masses may cause different chemical and hydrographic conditions, which leads to different levels of Chl a concentrations and primary production. It is worth to mention that offshore wind farm (OWF) construction in the Changyun Rise (CYR) of the Taiwan Strait is ongoing. As primary production is the foundation for a marine ecosystem and supports the food web and fish stock, the results of this research can not only be used as the baseline for evaluating the OWF impact on the marine ecosystem but also be used for assessing their influence on fishery resources.

The response of marine phytoplankton primary productivity to available light (photosynthesis-irradiance relationship, P B -E curve) is the principle physiology of plant that is particularly important in the estimation of primary production and in physicalbiogeochemical modeling. In this study, we conducted on-board incubation experiments to examine photosynthesis-irradiance relationships in samples collected from the subtropical shelf of the East China Sea during a winter cruise. Depth and spatial variation of the maximum photosynthesis rate normalized to chlorophyll a ( P m B ) and the initial slope (α) of the P B -E curve parameters were insignificant in the East China Sea. The vertical homogeneity was due to the strong winter mixing. However, spatial homogeneity could be possibly caused by different factors. With relatively low solar radiation in the winter, strong vertical mixing deteriorated light dose and may lead to homogeneously low photosynthetic parameters. In addition, differential inhibitions by temperature and nutrient availability may potentially cause the spatial homogeneity.The mean values of P m B and α were 2.82 ± 0.50 gC (gChl) -1 h -1 and 0.010 ± 0.002 gC (gChl) -1 h -1 (μmol photons m -2 s -1 ) -1 , respectively. Using the photosynthetic-irradiance model (P B -E curve model), the estimated value of shelf-averaged euphotic zone integrated primary production was 186 ± 117 mgC m -2 d -1 . With an overestimate of satellite-derived primary production, field observations will be required.

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