Monocarboxylic, dicarboxylic and hydroxy acids released by sequential treatments of suspended particles and sediments of the Black Sea

Highly variable mixtures of free and bound monocarboxylic, dicarboxylic and hydroxy acids are present in particulate matter from oxic and anoxic zones of the water column and underlying sediments of the Black Sea. Three pools of acids were obtained by sequential treatment: (1) an organic solvent-extractable free fraction, (2) an OH−-labile fraction released by alkaline hydrolysis of the solvent-extracted material, and (3) a H+-fraction obtained by acid hydrolysis of extracted and base-hydrolysed material. Monocarboxylic acids quantitatively dominated acid distributions in particles and sediments, but hydroxy [α-, β-, ω- and (ω-1)] acids were relatively enriched in particles from the anoxic zone and in sediments, reaching nearly 30% of total acids. β-Hydroxy acids were the most abundant hydroxy acids, being present in all particulate and sediment samples. α-, ω- and (ω-1)-Hydroxy acids were found only in sediments and then at low relative abundances. Distributions of carboxylic and hydroxy acids varied considerably between the three treatments and between oxic-zone particles, anoxic-zone particles, and sediment. Results are discussed in terms of biogeochemical mechanisms of differential production, degradation and preservation.