Comment on egusphere-2023-485

Le résumé fourni par la source

Abstract. Carbon and nitrogen dynamics in the Sea of Japan (SOJ) are rapidly changing. Here, we investigated the carbon and nitrogen isotope ratios of particulate organic matter (δ13CPOM and δ15NPOM, respectively) at the depth of ≤ 100 m in the southern part of the SOJ from 2016 to 2021. Both δ13CPOM and δ15NPOM exhibited multimodal distributions and were classified into four classes (I–IV) according to the Gaussian mixed model. Most of the samples were categorized into class II (n = 441), with the mean ± standard deviation (SD) of δ13CPOM and δ15NPOM of −23.7 ± 1.2 ‰ and 3.1 ± 1.2 ‰, respectively. Class I was characterized by low δ15NPOM (−2.1 ± 0.8 ‰, n = 11), class III by low δ13CPOM (−27.1 ± 1.0 ‰, n = 21), and class IV by high δ13CPOM (−20.7 ± 0.8 ‰, n = 34). Most of the class I samples were observed winter, and had similar temperature and salinity, and these indicated the Japanese local rivers' contributions to the class I formation. According to the generalized linear model (GLM), temperature and chlorophyll-a concentration all positively affected δ13CPOM, thus corroborating the hypothesis that active photosynthesis and phytoplankton growth increased δ13CPOM. However, the δ15NPOM variation was attributed to the temperature and salinity, not to nitrate concentration. To explain these unique δ15NPOM variations, a hypothesis is reasonable that multiple nitrate sources originated such as East China Sea, Kuroshio and the Japanese local rivers contribute to the primary production in the SOJ.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.