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.

Supplement to: Belyaeva, Alexandra N; Bobyleva, Nadezhda V (1981): Alkanes of plankton and bottom sediments from the Baltic Sea. Oceanology, 21(6), 712-715