抄録
The carbon isotopic characteristics (δ13C) of particulate organic matter during the summer blooming in Tokyo Bay have been investigated. The δ13C of suspended particulate organic matter (POM) in the surface seawater ranged from -15.4‰ to -4.5‰, which were considerably higher than the value generally known of planktonic organic matter (-20±1‰), suggesting that actively growing phytoplankton might be subjected to such a condition that the diffusion rate of CO2 might strongly limit the production of organic carbon. However, the isotope ratios of surfacial sedimentary organic matter ranged from -20.4‰ to -18.1‰, which were lower than those of POM. The δ13C of sinking organic particles collected in sediment traps were similar to those of POM. Therefore, the 13C-enriched isotope characteristics produced during summer phytoplankton blooming might be unlikely to be conserved in the sediments, possibly, by being mixed with terrestrial organic matter depleted in 13C, and/or, being rapidly decomposed during their sedimentation process. In conclusion, it was strongly suggested that properly determining the marine-endmember of δ13C should be important if the δ13C would be principally used to estimate contributions of terrestrially and in situ produced organic matter in such an exceedingly eutrophic coastal area as Tokyo Bay.
