Alkanes in plankton and bottom sediments of the Baltic Sea

Composition of alkanes present in total plankton was determined at two stations in the Gulf of Riga and in six samples of recent bottom sediments collected in a cross-section extending from the Daugava River estuary to the Gotland Basin. C15 to C17 n-alkanes were dominant in the plankton, the highest content being that of n-C16 alkanes. Low values of the index of predominance of odd hydrocarbons over even ones (0.95 to 1.16) and presence of phytane and of a chromatogram "hump" caused by compounds that cannot be separated by gas-liquid chromatography indicate partial contamination of the plankton with petroleum hydrocarbons. In the low-temperature part of the spectrum, the main n-alkane peak in the upper layer of bottom sediments is due to n-C17 compounds, whereas in the high-temperature part the main peak is due to a series of odd (C23-C31) n-alkanes. It was shown that alkanes present in these sediments have mixed biogenic origin (marine + terrigenous), with different ratios of autochtonous and allochtonous components in different parts of the investigated section, and that they are practically devoid of petroleum hydrocarbons.