Seasonal variations in the exchange of particulate organic matter between the East China Sea and the Northwest Pacific Ocean and the influencing factors

The exchange of particulate organic matter (POM) between the East China Sea (ECS) and the Northwest Pacific Ocean plays a crucial role in the material cycles in both the continental sea and the adjacent open ocean. Due to the limited observational data, the spatial and seasonal variations in the POM flux and their influencing factors remain unclear. In this study, a three-dimensional physical-biogeochemical coupled model was used to simulate the seasonal variations in marine biogenic POM flux across the 200-m isobath in the ECS. The POM flux across the 200-m isobath was low in the northeast of Taiwan, with the value <0.01 mmol/m²/s. The POM flux was high in the center of the section and the southwest of Kyushu, and exhibited distinct seasonal variations, with the maximum value of 0.20 mmol/m²/s in winter. The highest net export of POM occurred in winter, and the lowest occurred in autumn. The seasonal variations in POM fluxes were mainly attributed to the seasonal variations in POM concentrations along the 200-m isobath. Annually, 2.74 Tg C of POM (expressed in terms of carbon) was exported from the ECS to the Northwest Pacific Ocean, which accounts for 28 % of the net export across the three open boundaries (the Taiwan Strait, the 200-m isobath, and the Tsushima Strait) of the ECS, and was lower than the carbon fluxes at the air-sea interface and the river input.