Isotope variability of particulate organic matter at the PN section in the East China Sea

The source of particulate organic matter at the PN section in the East China Sea has been evaluated using stable carbon and nitrogen isotopes. The results showed that the δ13C and δ15N compositions varied from −19 to −31‰ and 0.7–9.5‰ respectively, and the isotope compositions were statistically distinct, enabling, by use of a simple components mixing equations, assessment of the ability of each tracer to estimate the terrestrial, Kuroshio Water, marine and remineralized sources' contributions. The dominance of terrestrial inputs of the Changjiang could be observed 250 km far from the river mouth in the East China Sea. In the shelf water column, the remineralization of biogenic organic matter becomes an important source except for the terrigenous and marine sources. The estimation of sources recorded by δ13C data was partly confirmed by equivalent δ15N and C/N compositions that reflected greater control by organic matter diagenesis and biological processing. However, the lighter contribution of δ13C data of the Kuroshio samples also indicates the alteration of the isotope values by microbial or other processes. The net export flux of POC in the PN section is estimated to be 4.1 kmol C/s and the annual export is 129 Gmol C/yr, which is account for 20% of the East China Sea.