Biogeochemical processes control the transport of organic pollutants in the upper Arctic Ocean

The Arctic Ocean is a mediterranean basin receiving pollutant inputs from the “double estuary” inflows (the Pacific water and Atlantic water), and the upper ocean plays a key role in transporting these compounds from the surface to their major sinks. Broad-scale spatial distributions and full-depth profiles of PAHs from the Pacific-Arctic-Atlantic are presented here, to better understand their vertical and lateral transport processes. Dissolved PAHs (0.3 to 10.2 ng L^-1, mean 4.3 ng L^-1) showed a decreasing trend along the Pacific-Arctic-Atlantic surface water, providing a background distribution in northern hemisphere’s oceans, despite several high values in the Arctic related to local inputs. PAHs in water columns were in “surface enrichment and depth-depletion” pattern, and mostly stored in the intermediate and deep water masses (~40 thousand tons in Central Arctic Ocean). Biological bump was suggested as an important driver for the transporting of semivolatile organic compounds. PAH sinking fluxes (2773±1259 ng·m^-2·d^-1), which were estimated by particle-reactive radioisotopes, showed the high scavenging efficiency, while lateral transport traced by transient tracers made a limited contribution to the PAH inventories in the Arctic surface ocean (87 tons yr^-1). Our study highlighted the fast and efficient biogeochemical transport compared with hydrological transport, in a prospective of time scale (1.3 and 14.6 years). With the fast changing in the Arctic, the effects of particle sinking or degradation will be probably strengthened, and the complicated modulation need to be further studied.