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The results of detailed isotopic studies of ice core samples from the Vostok station (East Antarctica) related to the MIS-11 era (the 11th sea isotope stage, i.e. 370–440 thousand years ago) are presented. Reconstruction of paleoclimatic conditions in this period of time was performed using the method of interpretation of the results of isotopic studies of ice, developed by the authors of the article, which is based on the joint analysis of three independent parameters: δD, d-excess, 17 O-excess. The isotopic composition (δD) and the deuterium excess depend on the following three meteorological parameters – the condensation temperature near the Vostok station, relative humidity, and the sea surface temperature at the source of moisture, whereas 17 O-excess depends only on the first two parameters. Accordingly, the proposed method of interpretation allows reconstructing the paleoclimatic conditions (the condensation temperature and surface air temperature at the Vostok station; sea surface temperature and relative humidity above the ocean) in two different regions in past epochs. For the first time, data on minor fluctuations in the relative humidity of the air in themoisture source throughout the MIS-11 era were obtained. The data resulted from the interpretation demonstrated that the relative humidity fluctuated within the measurement error of ±5%. Reconstructed climatic conditions in the era of MIS-11 were compared with published data for stations Vostok and Concordia, aswell as with the marine core data from 94-607 DSDP and ODP 177-1090. The results obtained on the basis of isotopic analysis of ice cores from stations Vostok and Concordia indicated that in the optimum MIS-11the air temperature was4 °C higher, and in the Termination V –8 °C lower than the present-day values. Thesimilarity of data between the marine columns DSDP 94-607 (North Atlantic), ODP 177-1090 (South Ocean)and our results points to the global nature of changes in the sea surface temperature during the MIS-11 era. The coordination of the above results proves the high quality of the methods developed by the authors for measuring and interpreting the isotope composition of ice.

In 2015–2016 during the research expeditions of Institute of Oceanology, Russian Academy of Sciences the study of stable water isotopes (18O and D) was conducted on glaciers of Novaya Zemlya. As a result, first data on isotopic composition of seasonal snow cover and glacial ice of different ages were obtained and its connection to recent climate change has been shown. The first studies of the isotopic composition of snow cover and glacial ice at Novaya Zemlya allowed determine the average values and the range of variability of δ18O and δD. It shown that for the Northern ice cap glacial ice δ18O vary within −13.91 ÷ −15.83 ‰ with an average value of −14.93 ‰ and −103,95 ÷ −116.75 ‰ for δD at −109.88 ‰ mean value. The maximum variations were recorded for summer snow samples (−8.35 ‰ for δ18O and −55.79 ‰ for δD), as well as for the horizon of superimposed ice (−20.67 ‰ for δ18O and −151.48 ‰ for δD) where isotopic composition has been inherited from winter precipitation. Insignificant differences in the coefficients of the meteoric water regression equation for precipitation on GNIP stations and glacial ice at Novaya Zemlya indicate similar conditions of air masses and precipitation formation both at GNIP station and on glaciers. Deuterium excess showed no seasonal fluctuations, and its values did not exceed 15 ‰, which shows that the proportion of continental precipitation of moisture is very low. Analysis of isotopic profiles obtained on the glaciers of Novaya Zemlya indicated the presence of significant melting. This applies not only to the modern shallow horizons, but also to the part of the glacial strata that formed in the highest part of the archipelago close to ice divide and came to the surface at the Serp i Molot Glacier tongue. Therefore, in terms of ice core palaeogeographic reconstructions the most interesting site is the highest part of the Northern ice cap where it is possible to assume the existence of colder horizons formed during the Little Ice Age and where the seasonal geochemical signal may be preserved.

Work on the project focused on the following five areas: 1) field works in Antarctica at Vostok and Concordia stations; 2) experimental and theoretical studies in the field of ice core and paleoclimate research; 3) experimental and theoretical works related to the exploration of subglacial Lake Vostok; 4) development of technology and drilling equipment for deep ice coring and exploration of subglacial lakes; 5) upgrading the analytical instrumentation in the Climate and Environmental Research Laboratory (CERL) of the Arctic and Antarctic Research Institute. The main achievements in the field of ice core and paleoclimate research include 1) further elaboration of a new method of ice core dating, which is based on the link between air content of ice and local insolation, 2) investigation of the possible applications of the 17O-excess measurements in ice core to the paleoclimate research, 3) a better understanding of the mechanisms of the formation of relief-related variations in the isotopic content of an ice core drilled in the area of Antarctic megadunes, and 4) obtaining the first reliable data set on the variations of the 17O-excess in the Vostok core corresponding to marine isotope stage 11. As part of our studies of subglacial Lake Vostok, we have obtained a large body of new experimental data from the new ice core recovered from the 5G-3 borehole to the surface of the subglacial lake. Stacked profiles of isotopic composition, gas content and the size and orientation of the ice crystals in the lake ice have been composed from the data of three replicate cores from boreholes 5G-1, 5G-2 and 5G-3. The study reveals that the concentration of gases in the lake water beneath Vostok is unexpectedly low. A clear signature of the melt water in the surface layer of the lake, which is subject to refreezing on the icy ceiling of Lake Vostok, has been discerned in the three different properties of the accreted ice (the ice texture, the isotopic and gas content of the ice). These sets of data indicate in concert that poor mixing of the melt (and hydrothermal) water with the resident lake water and pronounced spatial and/or temporal variability of local hydrological conditions are likely to be the characteristics of the southern end of the lake. A considerable part of the funding allocated by the RSF to this project was used for upgrading the analytical instrumentation for ice core studies in the CERL of AARI. Using this grant, we purchased and started working with the Picarro L-2140i, a new-generation laser mass analyzer, and set the upgraded mass spectrometer Delta V Plus into operation. The new equipment was used to carry out research planned as part of the project, including the setting up and carrying out of new measurements of 17О in ice cores.

Results of investigation of glacio-nival systems made in the Tabyn-Bogdo-Ola mountains (Western Mongolia) are presented in the paper. Average content of δ18О in the Tsagan-Us river water amounts to 17.44‰ that is almost equal to the isotope content in the clear glacier runoff near the edge of the Kozlov Glacier (−17.43‰). It means that the isotope content in water doesn’t significantly change over a distance of 30 km along the Tsagan-Us river. Hence, it appears that for this distance the river has no additional non-glacial feed. The magnitude 17.4±0.1‰ can be considered as the average content of isotopes in the glacio-nival system in the Tabyn-Bogdo-Ola mountain massif. This value can also be the precipitation-weighted average isotope content in the solid precipitations which are accumulated in glaciers of this massif. Seasonal isotope fluctuations are partly preserved in the snow-firn mass in the accumulation area of the Kozlov Glacier. A rate of annual accumulation was estimated by multiplying the apparent thickness (160 cm) of an annual layer into the snow density. According to our observations, it is equal to 800 mm w.e./year during 2013–2014. Accumulation is increased due to the wind and avalanche transportation of snow. During the ablation season, summer and spring snowfalls over the Kozlov Glacier area melt. Thus, it is possible to suppose that the autumn snowfalls play the important role in the accumulation. We may also suppose that the main source of the moisture for the Tabyn-Bogdo-Ola massif is located somewhere in the Inner Asia.

Petrographic studies performed on the continuous basis along the two ice cores obtained from holes 5G-1 and 5G-2 at Vostok Station has allowed to characterize with great details the evolution of the ice texture and fabric in the 232-m thick stratum of accreted ice formed from theLakeVostokwater. Conventionally the whole thickness of accreted ice is divided into two strata: lake ice 1 and lake ice 2. Lake ice 1 (3537–3618 m), formed in the sallow strait50 kmupstream of Vostok, is characterized by presence of disseminated mineral inclusions of Lake Vostok sediments, as well as of «water pockets» that represent frozen water inclusions trapped during the ice accretion. The latter constitute less than 1% of the total ice volume, their mean size is about0.5 cm. Gases trapped by «water pockets» during ice formation transform into crystalline inclusions of mixed gas hydrates. Accretion of lake ice 2 (3618–3769 m) proceeds in the deep part of the lake at a very small rate that does not assume trapping of liquid water inclusions and gases. Both strata of accreted ice are formed by orthotropic crystal growth from pure water. The main tendency in the evolution of accreted ice texture is growth of the mean crystal size with depth as the lake ice becomes younger towards the ice-water interface. The high-amplitude variations of crystal size and orientation observed around this general trend are shown to be linked with temporal and spatial variability of the supercooled melt-water flux from the northern part of the lake towards the ice formation site. The presence of supercooled water at the crystallization front supports persistent preferable growth of ice crystals with sub-horizontally oriented c-axes. The lack of supercooled water in turn support persistent growth of ice crystals with vertical or inclined with respect to the crystallization front c-axis orientation. It means that each of these preferred fabric orientations could serve as an indicator of intensity of melt water flux towards the ice formation site. After completing the isotope measurements on the 5G-2 ice core we plan to use the data on ice texture and fabric obtained in this study together with isotope data for thorough analysis of the peculiarities of water circulation in the southern part ofLakeVostok.

Temperature gradients in the upper layers of the snow pack are of importance for studying the emissivity properties of the snow surface with respect to microwaves used in remote sensing as well as for the heat and mass transfer in snow thickness. Gradients drive the initial snow microstructure metamorphisms that probably influence the firn properties in regard to air molecules fractionation and the air bubble enclosure process at close-off depths. As a contribution to investigation of these problems and following J.-M. Barnola initiative, we developed an autonomous recording system to monitor the temperature of the upper layers of the snow pack. The instrument was built to be autonomous and to be continuously operating within environmental conditions of the Antarctic plateau and the polar night. The apparatus which monitors temperature from the first 10 mof snow by 15 sensors of a «temperature grape» was set at Vostok station during 55 th Russian Antarctic Expedition within the frame of the French Russian collaboration (GDRI Vostok). From the available hourly measurements over the first year, we present preliminary results on the thermal diffusive properties of the snow pack as well as some character of the temperature variations on the Antarctic plateau.