Phenol compounds in the borehole 5G, Vostok station, after the unlocking of the subglacial lake

Abstract

The main results after the first unlocking into the subglacial Lake Vostok were as follows: the Lake had been opened and not polluted; the water pressure within the lake was not balanced by a column of the drilling liquid that resulted in unplanned rise of water in the borehole up to 340 m. The main problem during the drilling in the lake ice was to prevent a pollution of water by the drilling fluid, which filled the borehole, and thus, to avoid a compression of the fluid which could be the main source of chemical and biological pollution of not only the Lake itself, but also the Lake water samples and ice cores. The article presents results of analysis of causes for the occurrence of phenolic compounds in the central channel in the core of secondary ice, being formed by the lake water that rose into the well after the first penetration (the range of depths was 3426–3450 m). It was found that the process, running within the borehole during the drilling, can be described as the fractionation of phenolic compounds, being contained in the filling liquid, to the water phase with its subsequent freezing. We have developed methods for the determination of concentrations of phenolic compounds in the original aviation kerosene and Freon HCFC-141b: 6. mg·l−1 and 0.032 mg·l−1, respectively. To analyze the composition of phenolic compounds in the extract of real filling liquid, located at the bottom of the borehole, the method of gas chromatography-mass spectrometry (GC-MS) was used. The corresponding peaks were quite well resolved and identified as phenol and its derivatives. The main components of the extract were phenol (20%), 2.5-dimethyl phenol (23,8%), 2,4,6-trimethylphenol, and other congeners of phenol. In our case, the Lake Vostok was not polluted during both, the first and second penetrations, however, the problem of human impact on these pristine and unique subglacial reservoirs remains extremely relevant. This impact includes not only direct water pollution of the lake by the drilling fluid, but also possible changes in organic components of the liquid when contacting with the lake water under natural conditions of a deep well. Our data have demonstrated that using of such complex organic liquids, like aviation kerosene formerly used in many drilling projects, is undesirable when exploring deep Antarctic subglacial lakes. Thus, we come to the conclusion that the drilling fluid, currently used at the Vostok station (in the Vostok borehole), has to be replaced by another more inert fluid that would allow further research and exploration of the Lake Vostok.