Bacterial reworking of particulate organic matter in a dynamic marginal sea: Implications for carbon sequestration

Concentrations of particulate organic carbon (POC) and total hydrolyzable amino sugars (THAS) were measured along a transect of the dynamic South Yellow Sea (SYS) to investigate the bioreactivity and bacterial reworking of particulate organic matter (POM). Results showed that POM bioavailability was linked with primary production, as revealed by the significant correlation between chlorophyll-a concentrations and the diagenetic indicator glucosamine/galactosamine (GlcN/GalN). Production of bioavailable POM could rapidly stimulate microbial activity, generating hot spots of heterotrophic alteration. Lower GlcN/GalN ratios (<3) observed in the entire SYS indicate that POM underwent extensive microbial alteration. In particular, extremely low GlcN/GalN ratios (similar to 0.7) were found in the Yellow Sea Cold Water Mass, reflecting high bacterial alteration of POM. Estimates based on the bacterial biomarker muramic acid showed that on average similar to 13% of POM in the SYS was of bacterial origin. Elevated bacterial contributions were found in both nearshore and offshore areas. Strong mixing in the nearshore and the presence of cyclonic eddies in offshore waters may increase the residence time of POM in the water column and thus promote bacterial transformation of POM. Overall, our findings indicate that bacterial reworking of POM varies with productivity and that the extensive bacterial transformation of the remaining POM observed in the water column probably enhances long-term carbon sequestration.

Automated summary

Concentrations of particulate organic carbon (POC) and total hydrolyzable amino sugars (THAS) were measured along a transect in the South Yellow Sea (SYS) to study the reactivity and bacterial reworking of particulate organic matter (POM). The results showed that POM bioavailability was linked to primary production, as evidenced by the correlation between chlorophyll-a concentrations and the diagenetic indicator glucosamine/galactosamine (GlcN/GalN). Bacterial transformation of POM varied with productivity, and the extensive bacterial alteration of POM in the water column may enhance long-term carbon sequestration.