The modulation of marine biogeochemical cycles and ecosystem dynamics by physical oceanographic processes represents a core theme of contemporary interdisciplinary marine research. Material transport across key marginal sea passages provides a critical perspective for exploring physical-biogeochemical coupling mechanisms. As the only deep-water passage connecting the South China Sea (SCS) and the North Pacific Ocean for water mass and material exchange, the Luzon Strait features a vertical circulation pattern: inflow in the upper layer, outflow in the intermediate layer, and inflow in the deep layer. This transport structure constitutes the primary dynamic control on the nutrient budget of the SCS. Nevertheless, fine quantitative analysis remains lacking regarding the vertical stratification of nutrient transport, multi-scale variability, and its coupling with hydrodynamic processes under this circulation structure.

Using high-resolution output from the OFES2 numerical model, this study focuses on the main transect across the Luzon Strait. We calculate and analyze vertically stratified volume transport and nutrient flux throughout the entire water column, and systematically characterize the spatial patterns of multi-year mean states, interannual variability and long-term trends for hydrodynamic and biogeochemical variables, which facilitates in-depth analysis of multi-scale transport mechanisms. Layer-wise flux calculations reveal that the transport direction and vertical distribution of nutrient flux are not fully consistent with those of volume transport, indicating partial decoupling between advective physical transport and the biogeochemical distribution of nutrients. In terms of vertical disparities in seasonal variability, both volume transport and nutrient flux exhibit prominent seasonal signals in the surface layer, whereas such seasonal variations vanish in intermediate and deep waters. This suggests that material transport in subsurface layers is governed by distinct driving mechanisms other than surface dynamics.

Through refined stratified flux quantification, this study clarifies the vertical disparities and seasonal stratification of water and nutrient transport through the Luzon Strait. The findings offer solid data support for advancing our understanding of physical-biogeochemical coupling at marginal sea passages, and lay a foundation for future investigations into multi-scale regulatory mechanisms.