Organic carbon and total nitrogen contents and their isotope ratios were determined in a sediment core recovered from the Japan Sea to investigate the record of organic matter resources and paleoproductivity in a semi-enclosed marginal sea. δ13C-δ15N relationships show that the composition of sediment organic material resulted from the mixing of terrestrial and marine organic matter. We found synchronous down-core variations in the carbon and nitrogen isotope records, which are explained by surface productivity control on the composition of sediment organic material. Moreover, these variations are related to sea level changes, which caused variable surface water inflows. Last glacial sea-level lowering increased continental run-off, leading to water-column stratification in the Japan Sea. Anaerobic conditions due to basin-water stagnation led to the deposition of laminated clay. Sediment organic C/N and isotope ratios fluctuated markedly in the transitional stage from aerobic to anaerobic conditions. The fluctuations are likely to have been caused by large-scale oscillations in sea level just before the last glacial maximum.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Earth-Surface Processes