Fatty acid and sterol biomarkers as indicators of particulate matter source and alteration processes in the Black Sea

Fatty acids and sterols were measured in samples of particulate matter and surface sediments in the Black Sea to assess organic matter source and alteration processes in the water column, especially at the chemocline. Fatty acid and sterol distributions in particles in the oxiczone shallower than 100 m reflect their mixed plankton source coupled with aerobic decomposition of organic matter as particles sink. At the oxic-anoxic interface, the residual planktonic fatty acids were supplemented by fatty acids (e.g. iso- and nteiso-C l s and C17 , 1O-methyl-CI6 , 16: lw7 and 18:lw7)biosynthesized by anaerobic bacteria, most likely sulfate-reducing and phototrophic sulfur bacteria. inhabiting the top of the anoxic zone. The sterol composition changed notably by increased abundances of Sa(H)-stanols. presumably as anaerobic microbial alteration products of a5·stenols of planktonic origin. These bacterial biomarker fatty acids and sterols were predominantly associated with the slowly sinking <53-,umparticles, while the more rapidly sinking 53-,um particles apparently transited the anoxic zone with much less alteration in composition.