Distinct Source-Sink Patterns and Vertical Consumption of Alkyl and Aryl Organophosphate Esters in the Remote Ocean and Its Marginal Sea

Organophosphorus esters (OPEs) have been widely used as flame retardants and plasticizers and are globally ubiquitous. In the marine environment, OPEs primarily originate from continental sources and are initially confined to marginal seas before reaching remote oceans. However, their differing biogeochemical fates in these two regions remain unclear. This study investigated regional variations in the biogeochemical regulation mechanisms of OPEs (alkyl and aryl) across the Western Pacific and the South China Sea (112°E to 163°E) by analyzing their air-sea interface processes and vertical profiles. Results revealed that the South China Sea exhibited net inputs of OPEs (1.66 ± 1.36 μg m-2 d-1), while the Western Pacific mainly showed outputs (0.41 ± 1.15 μg m-2 d-1) to the atmosphere, forming patterns characterized by remote sources and marginal sinks. In vertical profiles, OPE consumption in the upper water column of the South China Sea was mainly driven by biodegradation, in contrast to the Western Pacific, where it was primarily controlled by the biological pump. This study reveals the distinct OPE fates in the remote ocean versus the marginal sea, highlighting the Western Pacific Warm Pool as a source of OPEs. Future research should address their marine coexistence with precursors and transformation products.