Search

A long‐standing enigma in oceanography is why terrestrial organic matter is "missing" in the global ocean, despite the considerable discharge into it every year. Although some explanations, such as mineralogical composition, hydrodynamic processes, and priming effect, have been proposed, we hypothesize that the essential mechanism behind the missing organic matter is microbial processing, for which the underlying coupled geochemical, molecular, and genetic evidence is unknown. An ultra‐large‐volume, long‐term river–seawater stratified simulation system was constructed to unravel the microbially driven fate of terrigenous particulate organic matter (POM) in oceans. Analysis of combining the molecular with POM chemical composition data suggests that Bacteroidetes could act as pioneers in the processing of terrigenous POM in oceans, degrading high‐molecular‐weight, high‐carbon compounds such as polysaccharides. Remaining low‐molecular‐weight nitrogenous organic matter is subsequently degraded by Planctomycetes and Proteobacteria. Isotopic signals show that this preferential degradation causes a distinct "aging" effect of POM, and along with nitrification enhanced by remineralization, causes a decrease in the POM C : N ratio. Degradation of terrigenous POM and bacterial biomass biosynthesis leads to positive deviations in δ15N and δ13C. Relatively refractory hydrocarbons, aromatic compounds, and phenols are accumulated by microbial processes in this system. This study provides mechanistic insights into the missing chemical and isotopic signals and microbially driven fate of terrigenous POM in the ocean, with important implications for how riverine material input affects marine carbon and nitrogen cycling. [ABSTRACT FROM AUTHOR]

The Ocean University of China radiocarbon Accelerator Mass Spectrometry center (OUC-CAMS) provides routine 14C analyses on bulk organic matter, black carbon, plant fragments, particulate organic matter and lipid biomarkers. The OUC-CAMS also provides reliable δ13C measurements simultaneously with 14C measurements. We report the standard operation procedures of sample pretreatments, process blank results and data quality of 14C analyses for over 2.5 years before 2022. We also report a comparison of δ13C results between standalone and simultaneously with 14C measurements. [ABSTRACT FROM AUTHOR]

The Ocean University of China radiocarbon accelerator mass spectrometer center (OUC-CAMS) is equipped with a mini carbon dating system (MICADAS) from the Ionplus AG. The MICADAS allows measurements of both graphite and CO 2 samples because of the design of a hybrid ion source. Also, both 13C and 14C of organic samples can be measured at the same time because a stand-alone IRMS is coupled to the MICADAS. The OUC-CAMS provides routine 14C analyses on bulk organic carbon of various types, such as sediments, particulate matter, plant fragments, and compound-specific lipid biomarkers. Here we report the performance based on continuous analysis of international reference materials of 195 graphite data and 605 gas data carried out over the 2.5 years before 2022. [ABSTRACT FROM AUTHOR]