Effect of anticyclonic eddies on the production and emission of marine dimethylsulfide in the northern South China Sea

Biogenic sulfide compounds, including dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide (DMSO), play a critical role in climate feedback and global sulfur cycles. Although the impact of mesoscale eddies on marine ecosystems is well established, their influence on sulfide compounds remains unclear. This study investigates the spatial distribution and key sink-source processes of DMS, DMSP, and DMSO in the South China Sea, a critical marginal sea of the western Pacific, during the summer of 2021, focusing on the influence of anticyclonic mesoscale eddies. We observed lower concentrations of these sulfides in the eddy core (for DMS, 1.80 ± 0.84 nmol L⁻¹, ranging from 0.66 to 2.95 nmol L⁻¹), whereas higher concentrations were found in the eddy edge (for DMS, 3.15 ± 2.17 nmol L⁻¹, ranging from 1.51 to 9.14 nmol L⁻¹). Notably, these compounds exhibited a distinct tendency to sink within the eddy core. This phenomenon can be attributed to the convergence and sinking of upper-layer water in the anticyclonic eddy core, which reduces nutrient availability in the upper layer, thereby affecting phytoplankton growth and altering the dominant species of phytoplankton. These changes in the phytoplankton community significantly impacted the source processes of DMS. The biological production rate of DMS was 53.3 % lower in the eddy core and 18.8 % higher at the eddy edge, compared to that in the reference sites. Furthermore, the difference between DMS production and total removal was largest at the eddy edge and smallest in the eddy core, shaping the observed DMS distribution pattern. Consequently, the diffusion of DMS from the sea to the atmosphere was reduced in the regions within the anticyclonic eddies. Our findings clarify the mechanisms through which mesoscale eddies affect the production and release of biogenic sulfides, underscoring the significant impact of mesoscale eddy processes on marine biogenic sulfides.