Aliphatic and polycyclic aromatic hydrocarbons in Black Sea sediments

Abstract

Concentrations of aliphatic hydrocarbons (AHC) in sediments of the Black Sea ranged from 153,000 ng g−1 dw near the mouth of the Danube River to about 10,000 ng g−1 dw in abyssal plain sediments. Compound distributions were dominated by long-chain n-alkanes except at the Danube station where a significant petrogenic component with an unresolved complex mixture was also present. Polycyclic aromatic hydrocarbon (PAH) concentrations ranged from 1,250 ng g−1 dw to about 200 ng g−1 dw at the same locations and compound distributions were dominated by PAH of pyrolytic origin. The flux of hydrocarbons to the central Black Sea sediments over the past 25 years is estimated to be ~ 580 μg AHC m−2 yr−1 and ~ 80 μg PAH m−2 yr−1. Long-range aeolian transport is invoked as the primary mechanism for delivering terrigenous higher plant AHC and pyrogenic PAH in abyssal Black Sea sediments although petrogenic hydrocarbons and retene appear to be delivered via fluvial transport and as a result are preferentially deposited in sediments along the continental margin. Analysis of a sediment core showed a rapid decrease in AHC and PAH concentrations with increasing depth in the sediment, reaching background levels of about 1000 ng g−1 dw and 10 ng g−1 dw, respectively, by about 4 cm depth or about 150 years BP. AHC fluxes in these sediments deposited before the industrial revolution were ~ 50 μg m−2 yr−1, PAH fluxes were ~ 0.5 μg m−2 yr−1. Differences between the distributions of AHC and PAH in surface sediments and the core sediments indicate an uncoupling of the source and transport processes affecting various components of the two hydrocarbon classes.