Dipole Eddies Change Per- and Polyfluoroalkyl Substances Spatial Profiles in the Western North Pacific Subtropical Gyre

Ocean currents are deemed as the main drivers for global distribution of per- and polyfluoroalkyl substances (PFAS). Mesoscale eddies are ubiquitous in the ocean and can strongly alter both horizontal and vertical circulation, thereby affecting PFAS distributions. A clear understanding of the influence of mesoscale eddies on PFAS distribution is critical for protecting ocean health, yet this influence remains poorly understood. In this study, we tracked a cyclone–anticyclone dipole eddy in the western North Pacific Subtropical Gyre, one of the most oligotrophic regions of the global ocean, and collected 72 samples from 12 stations (6 in the anticyclone, 3 in the cyclone, and 3 in the reference area (RA) outside the cyclone) at depths down to 1,000 m. Mesoscale eddies induced pronounced vertical and horizontal heterogeneity in PFAS concentrations. In the RA and cyclone, the highest concentrations of PFAS were found in the 50 m layer, while in the anticyclone, the maximum occurred in the deep chlorophyll maximum layer (100–131 m). This pattern can be attributed to upwelling in the cyclone, which impedes the downward transport of PFAS, whereas downwelling in the anticyclone facilitates it. Notably, the complex hydrodynamics at the interaction front of the dipole eddies led to PFAS concentrations 2–7 times higher than those in surrounding waters at the same depth. This created a pronounced PFAS hotspot and elevated the exposure risk for organisms abundant in the frontal zone. This study is the first observational investigation to decipher the impact of mesoscale eddies, one of the most widespread and important dynamical phenomena in the oceans, on PFAS distribution.