According to the GLM approach, environmental characteristics may explain approximately two-thirds of the variations in δ13CPOM. The relationships found in this study are consistent with previous observations. When environmental conditions were ignored, seasonal variation was significant; nevertheless, seasonal variation was not selected as an explanatory variable in the GLM, suggesting that environmental parameters can well explain the seasonality of δ13CPOM. The positive associations observed between temperature or chlorophyll-a concentration and δ13CPOM were similar to those observed in previous ocean and incubation experiments (Fontugne and Duplessy, 1981; Goericke and Fry, 1994; Miller et al., 2013; Savoye et al., 2003). Phytoplankton community growth rates are probably high in the warm water (Sherman et al., 2016), and high chlorophyll-a concentrations are considered to be a consequence of rapid phytoplankton growth. During the rapid growth phase, phytoplankton utilizes more 13CO2 utilization in the water, consequently elevating δ13CPOM (Freeman and Hayes, 1992).