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.

本研究测定了里加湾两处站位总浮游生物中的烷烃组成，并对沿道加瓦河河口至哥特兰盆地断面采集的6件现代海底沉积物样品中的烷烃组成进行了分析。浮游生物样本中以C15至C17正构烷烃（n-alkanes）为主，其中正构十六烷（n-C16）的含量最高。奇碳烃相较于偶碳烃的优势指数取值介于0.95至1.16之间，且检测到姥鲛烷（phytane）以及气液色谱（gas-liquid chromatography）无法分离的化合物所导致的色谱"鼓包"现象，上述特征表明浮游生物受到了石油烃的部分污染。在色谱谱图的低温区段，海底沉积物上层的正构烷烃主峰由n-C17类化合物贡献；而在高温区段，主峰则为一系列奇碳数（C23~C31）正构烷烃。研究表明，上述沉积物中的烷烃具有混合生物成因（海洋源+陆源），在研究断面的不同区域，自生与外源组分的占比存在差异，且这些沉积物几乎不含石油烃类。