The δ13CPOM and δ15NPOM varied from –29.3 to –17.7‰ and –3.2 to 6.7‰, respectively. In September 2020, the vertical profiles (0, 10, 30, 50, and 100 m depths and SCM) of δ13CPOM and δ15NPOM were collected at nine stations. SCM was observed at depths of 34–56 m. The differences in the δ13CPOM, δ15NPOM, and C:N ratios were significant among the layers according to ANOVA (p < 0.001). The δ13CPOM was the lowest at a depth of 50 m or SCM (mean ± SD: -25.7 ± 0.36‰ and –25.4 ± 0.45‰, respectively) (Fig. 2a). The δ13CPOM decreased with depth of up to 50 m (or SCM layer) and slightly increased at the 100-m depth (–24.2 ± 1.26‰). The δ15NPOM was the lowest at 10-m depth (1.5 ± 0.64‰), increased with depth, and the highest value was identified at the 100-m depth (5.0 ± 0.60‰) (Fig. 2b). The mean C:N ratio was estimated to 5.4–6.3 mol mol-1 except the 100-m depth with 4.2 ± 0.69 mol mol-1 (Fig. 2c). When the subsamples at the nine stations were regrouped into the surface (0 and 10 m depths) and subsurface (30 and 50 m and SCM) groups, the differences in both δ13CPOM and δ15NPOM were significant between the surface and subsurface (t-test, p ≤ 0.018). Therefore, δ13CPOM and δ15NPOM were different between the surface and subsurface, particularly during summer.