Characterisation of photo-oxidation and autoxidation products of phytoplanktonic monounsaturated fatty acids in marine particulate matter and recent sediments

Oxidation products of phytoplanktonic monounsaturated fatty acids have been detected in particulate matter and recent sediment samples collected at th e SOFI station (Gulf of Fos, Mediterranean Sea). The fluxes of these compou nds are not negligible and correspond to 0.14-0.03% of the total organic ca rbon flux in the zone investigated. Oxidation of monounsaturated fatty acid s results mainly in the production of isomeric allylic hydroperoxyacids, wh ich are relatively stable in the water column. Saturated hydroperoxyacids, epoxyacids and dihydroxyacids, deriving probably from the addition of hydro peroxides to the double bond of monounsaturated acids. have been detected a lso. During early diagenesis, hydroperoxides undergo heterolytic cleavage t o aldehydes and omega -oxocarboxylic or omega -hydroxycarboxylic acids, or homolytic cleavage and subsequent transformation to the corresponding alcoh ols or ketones. Due to the good preservation of their distribution pattern in Recent sediments, isomeric allylic hydroxyacids thus formed will constit ute more useful and specific tracers of oxidative processes than omega -oxo carboxylic or omega -dicarboxylic acids (with C-9 as the predominant specie s). These compounds will allow easy differentiation between autoxidative an d photooxidative processes and could thus provide a useful indication of th e residence time of particulate organic matter in the water column, the phy siological state of phytoplanktonic communities and current environmental p roblems related to ozone depletion. (C) 2001 Elsevier Science Ltd. All righ ts reserved.