Sources of Organic Tracers in Atmospheric Dust, Surface Seawater Particulate Matter and Sediment of the Red Sea

This chapter discusses the various input sources of extractable organic matter (EOM) compounds to the Red Sea. These are based on geochemical analyses of atmospheric dust, surface seawater particulate matter and sediment samples collected from the Gulf of Aqaba and the coasts of the Gulf of Suez, Saudi Arabia and Yemen. The samples were extracted with a dichloromethane/methanol mixture and analyzed by gas chromatography-mass spectrometry (GC-MS). The EOM compounds (lipids) in the samples are diverse and include n-alkanes, n-alkanoic acids, n-alkanols, methyl n-alkanoates, steroids, petroleum hydrocarbons and plasticizers. The steroids and n-alkanoic acids were major components of the surface seawater particulate matter samples, whereas petroleum hydrocarbons were major compounds in coastal sediments. Based on the results of the different samples, the main input sources of these lipids were from: (1) natural autochthonous microbiota (plankton and bacteria) as indicated by the presence of cholesterol and brassicasterol in the different surface seawater particulate matter and sediment samples; (2) natural allochthonous material origins from terrestrial plant detritus transported by dust as shown by the distributions of n-alkanoic acids, n-alkanols and phytosterols; and (3) anthropogenic sources (mainly petroleum) from regional oil production activities, oil tankers or shipping activities as revealed by the n-alkane distribution pattern and the presence of an unresolved complex mixture (UCM) of branched and cyclic hydrocarbons, with hopane and sterane biomarkers. Future studies of the organic and inorganic biogeochemistry on the water column, coastal areas and dust transported to the Red Sea are needed to characterize the various regional sources, transformation, and diagenetic processes of the organic matter en route to this marine environment.