Contents and stable isotopic compositions of organic carbon and total nitrogen in the surface sediment of two coastal bays in Korea

Surface sediment from the coastal bays of Gwangyang and Masan in South Korea were analyzed for their contents and isotopic values of organic carbon and total nitrogen. The sources and diagenetic alteration of organic matter were also assessed. Total organic carbon varied from 0.22% to 3.48% (average = 1.40%, n = 75), and C/N ratios varied from 2.4 to 15.2 (average = 8.79, n = 75). δ 13C org ranged from -19.92‰ to -25.86‰ (average = -21.21‰, n = 75), and δ 15N TN ranged from 8.57‰ to 3.93‰ (average = 6.49‰, n = 75). Total organic carbon in both areas was associated with grain-size, with higher contents in finer grained sediment. The high carbon content observed in Masan Bay sediment correlated with its higher C/N ratio. δ 13C org and δ 15N TN varied widely, attributable to various influences such as the input of terrestrial organic matter and diagenetic alteration. The depleted δ 13C org and higher δ 15N TN observed in the sediment of Gwangyang Bay reflected terrestrial supply, implying that biogeochemical processes, i. e. bacterial degradation, were more active in Masan Bay sediment, which showed less depleted δ 13C org and higher δ 15N TN than Gwangyang Bay sediment. δ 15N TN was the more useful indicator of biogeochemical processes in the highly anoxic sediment. These results indicate that the δ 13C org and δ 15N TN of sedimentary organic matter in coastal bays can indicate the source and degree of diagenetic alteration of sedimentary organic matter. © 2011 Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Netherlands.