Combined use of Δ14C and δ13C values to trace transportation and deposition processes of terrestrial particulate organic matter in coastal marine environments

Accelerator mass spectrometry was used to measure radiocarbons of riverine suspended particles and sediments from the estuary, continental shelf and slope off the coast of Tokachi River in Japan. The spatial distribution of Δ14C and δ13C values of sedimentary organic matter was divided into those of (1) estuary, (2) continental shelf, and (3) continental slope. For shelf sediments, respective maxima can be seen for Δ14C value, C/N ratio and organic carbon content at a station near the river mouth. The mean grain size of surface sediments also exhibits a similar trend. The δ13C values show a minimum near the river mouth. The shelf composition does not appear to be a simple mixture of terrestrial and marine origin. From the above data, it is considered that the spatial distribution of Δ14C and δ13C values may reflect variations in dispersion and deposition processes together with the size fractionation of riverine suspended particles, the resuspension of sediments, and differences in the contribution of marine organic matter.