Sources and downward fluxes of polycyclic aromatic hydrocarbons in the open southwestern Black Sea

The composition, abundance and fluxes of polycyclic aromatic hydrocarbons (PAHs) were investigated in time-series sediment traps set at 1000 m and 2000 m depth in the open southwestern Black Sea (October 2007–September 2008). Total PAH (TPAH22) concentrations ranged from 299–3540 ng g−1, averaging 1190 ± 698 ng g−1, while TPAH22 flux varied from 17.7–310 ng m−2 d−1, averaging 128 ± 86.6 ng m−2 d−1. Molecular profiles and diagnostic ratios of both low and high molecular weight compounds indicate the presence of PAHs derived from multiple pyrolytic/combustion sources (petroleum, grass, wood and coal combustion) and petrogenic sources (unburned fossil fuels). Temporal patterns of PAH loads/fluxes are linked to the variability in the magnitude of emissions and/or to the variability of mass flux, organic carbon flux and carbonate flux, the latter two being mostly controlled by marine productivity fluctuations. High biogenic fluxes observed in the Black Sea promote the vertical export of PAHs to deep Black Sea waters, enhancing also the transport of labile compounds at high flux seasons. Lateral transport/advection of PAHs seems also of importance at certain periods in deep Black Sea basins.