HYDROCARBON SOURCE IDENTIFICATION AND WEATHERING CHARACTERIZATION OF INTERTIDAL AND SUBTIDAL SEDIMENTS ALONG THE SAUDI-ARABIAN COAST AFTER THE GULF-WAR OIL-SPILL

One year after the Gulf War oil spill, approximately 200 intertidal an d subtidal (surface and subsurface) sediments were collected in the ar eas of Dawhat al Musallamiyah, Dawhat ad Dafi, and Ras Tanaqib along t he Saudi Arabian coast as part of the Nearshore Geochemistry Processes Study (Leg II: 16 March-5 April 1992) of the Mt Mitchell Gulf survey. The sediment samples were analysed for total petroleum hydrocarbons a nd the environmentally important saturated hydrocarbon (SHC) and polyc yclic aromatic hydrocarbon (PAH) components of the spilled oil. The ta rget analytes included n-alkanes (C-10-C34) and selected isoprenoids, individual and alkyl homologues of the two- through six-ringed PAH com pounds and sulphur-containing heterocyclic compounds (38 individual an d alkyl-PAHs), and selected cycloalkane biomarkers (steranes and trite rpanes). These target analytes were also determined for reference crud e oil samples. SHC, PAH alkyl homologue, and triterpane distributions in environmental samples were compared with reference crude oils-Kuwai t crude oil, Light Arabian crude oil, and Iranian crude oil-to determi ne the source(s) and extent of weathering of the spilled oil. Diagnost ic hydrocarbon parameters and ratios, especially the plots of the rati os of the C2- and C3-alkyl homologues of the dibenzothiophenes and phe nanthrenes/anthracenes (i.e., C2D/C2P vs. C3D/C3P) and the same homolo gues of the dibenzothiophenes and chrysenes/benzanthracenes (i.e., C2D /C2C vs. C3D/C3C), and the ratio of the source indicator triterpane/tr isnorhopanes, T(M)/T(S) were useful in differentiating hydrocarbon sou rce(s) and characterizing the weathering of the spilled oil in the sam ples. From the chemical diagnostic parameters, the Kuwait reference cr ude oil was determined to be very similar to the Gulf War spilled oil collected during a shoreline survey of oil-impacted beaches of Saudi A rabia in June 1991, shortly after the Gulf War. Asphaltic pavement res idual oil found at intertidal sites on Abu Ali and in isolated locatio ns in Dawhat ad Dafi were chemically identified using chemical biomark ers as originating from a source other than oil spilled from the Gulf War. With the SHC and PAH data, a set of chemical characteristics was identified that corresponded to stages of spilled oil weathering. Sedi ments from exposed habitats generally exhibited an advanced weathering stage; whereas, the moderately exposed and sheltered habitat sediment s were typically less weathered at a moderate weathering stage. The ad vanced stage of weathering was also apparent in the asphaltic pavement sediment. The hydrocarbon characteristics of the subtidal samples wer e usually dominated by background concentrations of hydrocarbons consi sting of both petrogenic PAH and biogenic saturated hydrocarbon signat ures.