Recent sediment accumulation and carbon burial in the East China Sea

Sediment and carbon budgets were constructed for the East China Sea (ECS) Shelf based on up-to-date data. The total annual sediment flux in the ECS Shelf is approximately 96% of the terrestrial input. There is high retention of sediment on the ECS Shelf owing to the broad nature of the shelf edge (i.e., 500-600 km) and because of an along-shore sediment dispersal path driven by the East China Sea Coastal Current (ECSCC) and the Taiwan Warm Current (TWC). Organic carbon (OC) burial was also observed, based on the results for sediment accumulation and the OC proportion in surface sediment. A total of 7.4 × 10⁶ t of OC is preserved in shelf sediments. Source discrimination of sedimentary OC revealed that the percentage of OC burial for both terrigenous and marine OC sources was higher than the global mean value, at 10% and 5.5%, respectively, presumably owing to high sediment accumulation. High OC flux to sediment in the estuary and shelf break suggests that riverine discharge and upwelling of the Kuroshio intrusion are key factors regulating OC burial over the shelf. Estimated using a mass balance model, 15-20% of the carbon inventory is buried in the shelf sediment, while >80% of the carbon inventory must be transported out of shelf area in the form of dissolved carbon (organic and inorganic). The accumulation of carbon in sediments and the outflow of dissolved carbon sustain a high carbon sink in the ECS.