The biogeochemical processes of polycyclic
aromatic hydrocarbons
(PAHs) in the South China Sea (SCS) are influenced by the exchanges
of water masses, energies, and materials between this marginal sea
and the Pacific Ocean. To investigate the impact of oceanic water
intrusion on semivolatile compounds, we collected seawater samples
in the Western Pacific, northern, and central SCS in 2017 and analyzed
for dissolved PAHs. PAH concentrations in the water columns of the
Pacific Ocean and SCS were 1.7–11 and 1.1–7.3 ng L–1, respectively, showing spatial distinctions in terms
of the composition and source characteristics. A common depletion
for three-ring PAHs was found in the northern SCS by comparing the
modeling results of conservative mixing by Kuroshio intrusion. Kuroshio
water increased the levels of temperature, dissolved oxygen, and nutrients
when intruding into the northern SCS and was likely to enhance the
bioavailability of PAHs and stimulate their biodegradation process.
In the water column, the most effective layer under the Kuroshio intrusion
impact is different for three- and four-ring PAHs, where the three-ring
PAHs’ depletion was most significant at the surface; however,
for four-ring PAHs, that was at the deep chlorophyll maximum layer.
This study highlighted the effect of ocean currents on PAHs for their
water-column processes both from physical and biogeochemical perspectives.