Seasonal variations and sources of sedimentary organic carbon in Tokyo Bay

Total organic carbon (TOC), total nitrogen (TN) contents, their stable C and N isotope ratio (δ13C and δ15N), and chlorophyll a ([Chl a]sed) of surface sediments were investigated monthly to identify the seasonal variations and sources of organic matter in Tokyo Bay. The sedimentary TOC (TOCsed) and TN (TNsed) contents, and the sedimentary δ13C and δ15N (δ13Csed and δ15Nsed) values were higher in summer than other seasons. The seasonal variations were controlled by high primary production in the water column and hypoxic water in the bottom water during summer. The fraction of terrestrial and marine derived organic matter was estimated by Bayesian mixing model using stable isotope data and TOC/TN ratio. Surface sediments in Tokyo Bay are dominated by marine derived organic matter, which accounts for about 69 ± 5% of TOCsed.