Dissolved PAHs impacted by air-sea interactions: Net volatilization and strong surface current transport in the Eastern Indian Ocean

Abstract

In the Indian Ocean, the marine fate of polycyclic aromatic hydrocarbons (PAHs) is impacted by the unique air-sea interactions with great monsoon characters. By collecting water-column samples during the monsoon transition period, we found PAHs (∑8PAH: 1.1–27 ng L−1) showed significantly different distributions from the Bay of Bengal, Equatorial Indian Ocean, Eastern Indian Ocean, and the South China Sea (p < 0.001). Their vertical profiles showed natural logarithm relationships with depth in the Bay of Bengal and Equatorial Indian Ocean. PAHs were mainly from wood/coal combustion and vehicle emission. The estimation of PAHs’ air-seawater exchange flux revealed net volatilizations from seawater except in the Eastern Indian Ocean. The Wyrtki Jet, a surface current driven by the westerly wind, was observed in the equatorial area. This swift current could transport PAHs eastward efficiently with a mass flux of 636 ± 188 g s−1. The subsurface current, Equatorial Undercurrent, played a less crucial role in PAHs’ lateral transport with a flux of 115 ± 31.3 g s−1. This study preliminarily revealed the role of air-sea interactions on PAHs’ transport and fate in the open ocean. The coupled air-sea interactions with biogeochemical processes should be considered in future work.