Carbon and nitrogen stable isotope ratios of particulate organic matter in the southern Sea of Japan from 2018 to 2021

Carbon and nitrogen stable isotope ratio of particulate organic matter (POM) was collected in the surface layer of the southern Sea of Japan. 0.9–11.5 L of seawater was filtered using a pre-combusted (450 °C, 6 h) glass fiber filter (GF/F, Whatman), and the carbon and nitrogen isotopic ratios were measured using an Isoprime 100 isotopic ratio mass spectrometer (Elementar, Langenselbold, Germany). The carbon: nitrogen ratio (C: N ratio) of POM occasionally showed outlier values. Therefore, the means and standard deviations (SDs) of the C: N ratio were calculated, and samples whose C: N ratio differed by > 3 × SD from the mean value were eliminated. With the POM, temperature, salinity, chlorophyll a concentration, and nutrient concentrations were measured.