The three-dimensional transport and fate of persistent organic pollutants (POPs) in the ocean are governed by complex physical and biogeochemical interactions. Using a high-resolution, three-dimensional coupled hydrodynamic-biogeochemical-POPs model, this study systematically elucidates the multiscale transport mechanisms of POPs across the Northwestern Pacific Ocean (NWPO) and its marginal seas, tracing their pathways from the surface to deep-ocean sinks.
In the surface layer, POPs transport is primarily governed by the interplay between strong boundary currents and air-sea exchange fluxes. We demonstrate that the intense Kuroshio actively modulates regional air-sea exchange; its rapid advective timescale continuously overrides local air-sea equilibria, driving significant basin-scale horizontal transport.
As pollutants penetrate the subsurface, their vertical distribution and deep accumulation are intricately regulated by ocean stratification, complex water mass dynamics, and the biological pump. In the open NWPO, the physical subduction of the North Pacific Intermediate Water (NPIW) and Subtropical Mode Water (STMW) primarily drives the downward transport and ventilation of POPs. Concurrently, the biological pump exerts strong biogeochemical control: POPs (e.g., PCB-153) are preferentially scavenged by sinking particulate organic matter during massive phytoplankton blooms. Subsequent subsurface remineralization below the stratified layers releases these congeners back into the dissolved phase, structurally modifying deep concentration profiles.
Ultimately, we reveal a fundamental mechanistic divergence in deep accumulation between the open ocean and semi-enclosed marginal seas. In the open NWPO, the combination of strong physical advection and the subduction of NPIW and STMW promotes continuous lateral dispersion. In contrast, within the semi-enclosed Sea of Japan, strict topographic constraints coupled with regional stratification foster a distinct mid-depth (100–600 m) accumulation zone. Here, deep accumulation is heavily dependent on the synergistic retention by local vertical advection and the biological pump. By comparing the characteristic timescales of horizontal advection and vertical particle settling, this study provides a comprehensive paradigm for understanding how varying oceanic regimes shape the long-term sequestration of anthropogenic contaminants.