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This paper documents the drilling of the 5G deep hole at the Russian Vostok station, Antarctica. The hole construction is described and the specifications of the drill and surface drilling equipment are given. The peculiarities of drilling at various depths are considered. Based on the extensive experimental data collected at Vostok station, the processes occurring at the hole bottom are investigated: ice breaking and cutting, bottom cleaning and chip transport, and accumulation of the chips in the screen. The main factors affecting ice-drilling efficiency are the coarseness of ice crystals and the ice temperature. When ice crystal size exceeds 10 mm the cutting efficiency sharply decreases, and when ice temperature exceeds -5°C the chip transport from the hole bottom and the chip density in the screen are reduced. The drill advance then becomes irregular, slows down and may even be terminated in some cases. Optimal values of the basic drilling parameters (e.g. cutter head rotation rate and drilling fluid flow rate in the circulation system) have been deduced empirically. The designs of the cutter head and circulation system including screens have been significantly modified, allowing the drilling process to proceed at a normal rate even in the vicinity of the subglacial lake surface. [ABSTRACT FROM AUTHOR]

The article presents the first seasonal variations of 17O-excess and d-excess to offer an analogy with glacial climatic conditions in Vostok Station, Antarctica on an event basis over one year. It mentions that the 17O-excess and d-excess variations can be explained through the influence of low temperatures' kinetic fractionation. It states that the comparison with simple isotopic models affirms the explanation, but cannot explain the association between temperature, 17O-excess and d-excess without a particular relationship between surface temperature and condensation.