Vertical fluxes of aromatic and aliphatic hydrocarbons in the Northwestern Mediterranean Sea.

Aliphatic and aromatic hydrocarbon fluxes were measured in time series sediment trap samples at 200 m and at 1000 m depths in the open Northwestern Mediterranean Sea, from December 2000 to July 2002. Averaged fluxes of n-alkanes, UCM and T-PAH(35) were 2.96 ± 2.60 µg m(-2) d(-1), 64 ± 60 µg m(-2) d(-1) and 0.68 ± 0.59 µg m(-2) d(-1), respectively. Molecular compositions of both hydrocarbon classes showed a contamination in petrogenic hydrocarbons well above the background levels of such an open site, whereas pyrolytic hydrocarbons stand in the range of other open Mediterranean locations. Fluxes displayed ample interannual and seasonal variabilities, mainly related to mass flux variation while concentration evolutions trigger secondary changes in pollutant fluxes. High lithogenic flux events exported particles with a larger pollutant load than biogenic particles formed during the spring bloom and during the summer. Sinking hydrocarbons were efficiently transported from 200 m to 1000 m.

PAH transport by sinking particles in the open Mediterranean Sea: a 1 year sediment trap study.

One year time series of sinking particles were collected at two depths in the open Mediterranean Sea and analysed for polycyclic aromatic hydrocarbons (PAH). Average total PAH concentrations were 593+/-284 ng g(-1) at 250 m and 551 +/- 198 ng g(-1) at 2850 m. Total PAH fluxes averaged 73 +/- 58 ng m(-2) d(-1) at 250 m and 53 +/- 39 ng m(-2) d(-1) at 2850 m. Contamination levels and, thus, exposure of marine organisms to PAH are comparable in surface and deep waters. Deep waters appear as a significant, yet overlooked, PAH sink. PAH temporal patterns show noticeable seasonality. This is partly due to varying levels of specific components such as the winter increase of pyrolytic PAH. Downward transport processes and the nature of sinking particles also impact on PAH fluxes, as inferred during periods of increasing productivity. Different phase-associations and interactions with particulate organic carbon for low-MW fossil PAH and high-MW pyrolytic PAH influence their downward transport efficiency.