Deposition in the deep ocean plays a crucial role in the global sink of persistent organic pollutants (POPs), yet observation-based assessments of their biogeochemical cycling are scarce. In this study, surface sediments were collected from deep sea of the Eastern Indian Ocean (2,161–4,545 m) and analyzed for organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). Long-range atmospheric transport was identified as the dominant pathway for OCPs (36.7–762.0 pg/g) and PCBs (25.5–110.0 pg/g) to reach the basin area from surrounding agricultural, manufacturing, and combustion emissions. Besides the TOC-dependent deposition, unique hydrodynamic conditions in the mid-ocean ridge might influence the transport and accumulation of POPs by altering their resuspension and repartitioning processes. Additionally, results of the machine learning analysis suggested that logK_OW, TOC content, and pollutant residence time in the ocean are important parameters in determining PCB concentrations in the Indian Ocean. This study revealed the biogeochemical controls on the deposition of OCPs and PCBs in the Indian Ocean by combining field observation and model simulation. Given the rapid rate of surface warming and various biogeochemical responses in the Indian Ocean, it is recommended to conduct long-term, high-resolution field observations to understand the dynamic fate of POPs in these changing ocean environments.

Indian Ocean,PCBs,OCPs,Machine Learning