Distribution and biological turnover of dissolved organic compounds in the water column of the Black Sea

(a) Uptake rates of organic compounds were from 2 to 4640 times faster in oxic surface waters than in anoxic waters. (2) Sharp maxima or minima in concentrations of organic compounds coincided with zones of enhanced microbial activities. (3) The benthic boundary layer, 300-400 m thick, had a markedly different organic composition and substantially higher concentrations of organic acids, than the overlying water. (4) A dramatic change in the composition and concentration of dissolved free amino acids occurred in the water column. (5) Organic thiols constituted a significant portion (e.g. 10-20%) of the total reduced sulfur near the top of the sulfidic zone. (6) Major unknown amine and carbonyl compounds were discovered in the anoxic zone. -from Authors