Organic matter sources and early diagenetic alterations in Arctic surface sediments (Lena River delta and Laptev Sea, Eastern Siberia)—I. Analysis of the carboxylic acids released via sequential treatments

The acid moieties occurring in marine, arctic, and surface sediments from the Lena River delta and adjacent Laptev Sea were analyzed by sequential treatments. Five acid fractions, corresponding to distinct pools, were thus obtained from each sample: the unbound acids (isolated from extracts), the OH−-labile acids (released by a classical saponification on the insoluble residue), the OH−(PTC)-labile acids (obtained via an additional saponification with a phase transfer catalyst), the H+-labile acids (released by a subsequent acid hydrolysis) and, finally, the tightly bound acids (only released by thermolysis). The existence of these different pools reflects differences in the mode of occurrence of the acids and/or in the protection provided by the (macro)molecular structures which they are linked to. To the best of our knowledge this study is the first example of a complete quantitative and qualitative analysis of acid moieties in recent sediment samples. Information was thus derived on (i) the relative importance of microalgal, bacterial and terrestrial contributions and the types of organisms implicated, (ii) the extent of early diagenetic alterations, (iii) the variations in the above features depending on the considered sample and pool and (iv) the mechanism of OM preservation and the control of TOC values and total fatty acids contents in such surficial sediments.