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Pingos are common features in permafrost regions that form by subsurface massive-ice aggradation and create hill-like landforms. Pingos on Spitsbergen have been previously studied to explore their structure, formation timing and connection to springs as well as their role in postglacial landform evolution. However, detailed hydrochemical and stable-isotope studies of massive-ice samples recovered by drilling have yet to be used to study the origin and freezing conditions in pingos. Our core record of 20.7 m thick massive pingo ice from Grøndalen is differentiated into four units: two characterised by decreasing δ18O and δD and increasing d (units I and III) and two others showing the opposite trend (units II and IV). These delineate changes between episodes of closed-system freezing with only slight recharge inversions of the water reservoir and more complicated episodes of groundwater freezing under semi-closed conditions when the reservoir was recharged. The water source for pingo formation shows similarity to spring water data from the valley with prevalent Na+ and HCO3- ions. The sub-permafrost groundwater originates from subglacial meltwater that most probably followed the fault structures of Grøndalen and Bøhmdalen. The presence of permafrost below the pingo ice body suggests that the talik is frozen, and the water supply and pingo growth are terminated. The maximum thaw depth of the active layer reaching the top of the massive ice leads to its successive melt with crater development and makes the pingo extremely sensitive to further warming.

The oldest ice core records are obtained from the East Antarctic Plateau. Water isotopes are key proxies to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in trajectory-based Rayleigh distillation and isotope-enabled climate models. However, a quantitative understanding of processes potentially altering snow isotopic composition after deposition is still missing. In low-accumulation sites, such as those found in East Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretability of an ice core's isotopic composition.By combining observations of isotopic composition in vapour, precipitation, surface snow and buried snow from Dome C, a deep ice core site on the East Antarctic Plateau, we found indications of a seasonal impact of metamorphism on the surface snow isotopic signal when compared to the initial precipitation. Particularly in summer, exchanges of water molecules between vapour and snow are driven by the diurnal sublimation–condensation cycles. Overall, we observe in between precipitation events modification of the surface snow isotopic composition. Using high-resolution water isotopic composition profiles from snow pits at five Antarctic sites with different accumulation rates, we identified common patterns which cannot be attributed to the seasonal variability of precipitation. These differences in the precipitation, surface snow and buried snow isotopic composition provide evidence of post-deposition processes affecting ice core records in low-accumulation areas.

Climate trends in the Antarctic region remain poorly characterized, owing to the brevity and scarcity of direct climate observations and the large magnitude of interannual to decadal-scale climate variability. Here, within the framework of the PAGES Antarctica2k working group, we build an enlarged database of ice core water stable isotope records from Antarctica, consisting of 112 records. We produce both unweighted and weighted isotopic (δ18O) composites and temperature reconstructions since 0 CE, binned at 5- and 10-year resolution, for seven climatically distinct regions covering the Antarctic continent. Following earlier work of the Antarctica2k working group, we also produce composites and reconstructions for the broader regions of East Antarctica, West Antarctica and the whole continent. We use three methods for our temperature reconstructions: (i) a temperature scaling based on the δ18O–temperature relationship output from an ECHAM5-wiso model simulation nudged to ERA-Interim atmospheric reanalyses from 1979 to 2013, and adjusted for the West Antarctic Ice Sheet region to borehole temperature data, (ii) a temperature scaling of the isotopic normalized anomalies to the variance of the regional reanalysis temperature and (iii) a composite-plus-scaling approach used in a previous continent-scale reconstruction of Antarctic temperature since 1 CE but applied to the new Antarctic ice core database. Our new reconstructions confirm a significant cooling trend from 0 to 1900 CE across all Antarctic regions where records extend back into the 1st millennium, with the exception of the Wilkes Land coast and Weddell Sea coast regions. Within this long-term cooling trend from 0 to 1900 CE, we find that the warmest period occurs between 300 and 1000 CE, and the coldest interval occurs from 1200 to 1900 CE. Since 1900 CE, significant warming trends are identified for the West Antarctic Ice Sheet, the Dronning Maud Land coast and the Antarctic Peninsula regions, and these trends are robust across the distribution of records that contribute to the unweighted isotopic composites and also significant in the weighted temperature reconstructions. Only for the Antarctic Peninsula is this most recent century-scale trend unusual in the context of natural variability over the last 2000 years. However, projected warming of the Antarctic continent during the 21st century may soon see significant and unusual warming develop across other parts of the Antarctic continent. The extended Antarctica2k ice core isotope database developed by this working group opens up many avenues for developing a deeper understanding of the response of Antarctic climate to natural and anthropogenic climate forcings. The first long-term quantification of regional climate in Antarctica presented herein is a basis for data–model comparison and assessments of past, present and future driving factors of Antarctic climate.

A 181.8 m ice core was recovered from a borehole drilled into bedrock on the western plateau of Mt El'brus (43°20′53.9′′ N, 42°25′36.0′′ E; 5115 m a.s.l.) in the Caucasus, Russia, in 2009 (Mikhalenko et al., 2015). Here, we report on the results of the water stable isotope composition from this ice core with additional data from the shallow cores. The distinct seasonal cycle of the isotopic composition allows dating by annual layer counting. Dating has been performed for the upper 126 m of the deep core combined with 20 m from the shallow cores. The whole record covers 100 years, from 2013 back to 1914. Due to the high accumulation rate (1380 mm w.e. year−1) and limited melting, we obtained isotopic composition and accumulation rate records with seasonal resolution. These values were compared with available meteorological data from 13 weather stations in the region and also with atmosphere circulation indices, back-trajectory calculations, and Global Network of Isotopes in Precipitation (GNIP) data in order to decipher the drivers of accumulation and ice core isotopic composition in the Caucasus region. In the warm season (May–October) the isotopic composition depends on local temperatures, but the correlation is not persistent over time, while in the cold season (November–April), atmospheric circulation is the predominant driver of the ice core's isotopic composition. The snow accumulation rate correlates well with the precipitation rate in the region all year round, which made it possible to reconstruct and expand the precipitation record at the Caucasus highlands from 1914 until 1966, when reliable meteorological observations of precipitation at high elevation began.

We present the results of glaciological investigations in the megadune area located 30 km to the east of Vostok Station (central East Antarctica) implemented during the 58th, 59th and 60th Russian Antarctic Expedition (January 2013–2015). Snow accumulation rate and isotope content (δD, δ18O and δ17O) were measured along the 2 km profile across the megadune ridge accompanied by precise GPS altitude measurements and ground penetrating radar (GPR) survey. It is shown that the spatial variability of snow accumulation and isotope content covaries with the surface slope. The accumulation rate regularly changes by 1 order of magnitude within the distance δD and 17O-excess ∕ δD slopes (where dxs = δD − 8 ⋅ δ18O and 17O-excess = ln(δ17O ∕ 1000 + 1) −0.528 ⋅ ln (δ18O ∕ 1000 + 1)), we conclude that the spatial variability of the snow isotopic composition in the megadune area could be explained by post-depositional snow modifications. Using the GPR data, we estimated the apparent dune drift velocity (4.6 ± 1.1 m yr−1). The full cycle of the dune drift is thus about 410 years. Since the spatial anomalies of snow accumulation and isotopic composition are supposed to drift with the dune, a core drilled in the megadune area would exhibit the non-climatic 410-year cycle of these two parameters. We simulated a vertical profile of snow isotopic composition with such a non-climatic variability, using the data on the dune size and velocity. This artificial profile is then compared with the real vertical profile of snow isotopic composition obtained from a core drilled in the megadune area. We note that the two profiles are very similar. The obtained results are discussed in terms of interpretation of data obtained from ice cores drilled beyond the megadune areas.

The isotopic compositions of oxygen and hydrogen in ice cores are invaluable tools for the reconstruction of past climate variations. Used alone, they give insights into the variations of the local temperature, whereas taken together they can provide information on the climatic conditions at the point of origin of the moisture. However, recent analyses of snow from shallow pits indicate that the climatic signal can become erased in very low accumulation regions, due to local processes of snow reworking. The signal-to-noise ratio decreases and the climatic signal can then only be retrieved using stacks of several snow pits. Obviously, the signal is not completely lost at this stage, otherwise it would be impossible to extract valuable climate information from ice cores as has been done, for instance, for the last glaciation. To better understand how the climatic signal is passed from the precipitation to the snow, we present here results from varied snow samples from East Antarctica. First, we look at the relationship between isotopes and temperature from a geographical point of view, using results from three traverses across Antarctica, to see how the relationship is built up through the distillation process. We also take advantage of these measures to see how second-order parameters (d-excess and 17O-excess) are related to δ18O and how they are controlled. d-excess increases in the interior of the continent (i.e., when δ18O decreases), due to the distillation process, whereas 17O-excess decreases in remote areas, due to kinetic fractionation at low temperature. In both cases, these changes are associated with the loss of original information regarding the source. Then, we look at the same relationships in precipitation samples collected over 1 year at Dome C and Vostok, as well as in surface snow at Dome C. We note that the slope of the δ18O vs. temperature (T) relationship decreases in these samples compared to those from the traverses, and thus caution is advocated when using spatial slopes for past climate reconstruction. The second-order parameters behave in the same way in the precipitation as in the surface snow from traverses, indicating that similar processes are active and that their interpretation in terms of source climatic parameters is strongly complicated by local temperature effects in East Antarctica. Finally we check if the same relationships between δ18O and second-order parameters are also found in the snow from four snow pits. While the d-excess remains opposed to δ18O in most snow pits, the 17O-excess is no longer positively correlated to δ18O and even shows anti-correlation to δ18O at Vostok. This may be due to a stratospheric influence at this site and/or to post-deposition processes.

A 182 m ice core was recovered from a borehole drilled into bedrock on the western plateau of Mt. Elbrus (43°20´53.9'' N, 42°25´36.0'' E; 5115 m a.s.l.) in the Caucasus, Russia, in 2009. This is the first ice core in the region that represents a paleoclimate record that is practically undisturbed by seasonal melting. Relatively high snow accumulation rates at the drilling site enabled the analysis of the intraseasonal variability in climate proxies. Borehole temperatures ranged from −17 °C at 10 m depth to −2.4 °C at 182 m. A detailed radio-echo sounding survey showed that the glacier thickness ranged from 45 m near the marginal zone of the plateau up to 255 m at the glacier center. The ice core has been analyzed for stable isotopes (δ18O and δD), major ions (K+, Na+, Ca2+, Mg2+, NH4+, SO42-, NO3-, Cl-, F-), succinic acid (HOOCCH2COOH), and tritium content. The mean annual net accumulation rate of 1455 mm w.e. for the last 140 years was estimated from distinct annual oscillations of δ18O, δD, succinic acid, and NH4+. Annual layer counting also helped date the ice core, agreeing with the absolute markers of the tritium 1963 bomb horizon located at the core depth of 50.7 m w.e. and the sulfate peak of the Katmai eruption (1912) at 87.7 m w.e. According to mathematical modeling results, the ice age at the maximum glacier depth is predicted to be ~ 660 years BP. The 2009 borehole is located downstream from this point, resulting in an estimated basal ice age of less than 350–400 years BP at the drilling site. The glaciological and initial chemical analyses from the Elbrus ice core help reconstruct the atmospheric history of the European region.

Modeling the isotopic composition of atmospheric precipitation is an important tool for climatic, paleoclimatic and hydrological studies. This paper presents an improved simple model of the isotopic composition of precipitation in Central Antarctica. It differs from the previous version published by Salamatin et al. (2004) by 1) the included geochemical cycle of oxygen 17 and 2) the possibility of solving the inverse problem (i.e., finding the trajectory parameters that could form the isotopic composition of the precipitation observed at the end of the trajectory). The paper examines in detail the main tuning parameters of the model, among which the most important are the temperature and humidity in the moisture source, the “circulation parameter”, which takes into account the advection of vapor into the moisture source, the condensation temperature and the degree of air supersaturation with moisture in ice clouds. Based on the analysis of data on the isotopic composition (including “excess of oxygen 17”, 17O-xs) of water vapor in the surface layer of the atmosphere over the ocean and surface snow sampled along meridional profiles in East Antarctica, the optimal tuning of the model for calculating the isotopic composition of atmospheric precipitation at the Antarctic Vostok station was performed. In particular, it is shown that the temperature and humidity of the air in the moisture source are +17.4°C and 72%, respectively, and the condensation temperature is –41.3°C. The possibilities of using the model to analyze the isotopic composition of liquid precipitation falling on other continents are discussed. The final part of the paper discusses the limitations of the model. In particular, it is noted that the model does not take into account such processes as the evaporation of precipitation when it falls in arid conditions, mixing of trajectories, the influence of local sources of moisture, as well as the features of isotope fractionation during the evaporation of moisture from the continents.

We compare the present and last interglacial periods as recorded in Antarctic water stable isotope records now available at various temporal resolutions from six East Antarctic ice cores: Vostok, Taylor Dome, EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML), Dome Fuji and the recent TALDICE ice core from Talos Dome. We first review the different modern site characteristics in terms of ice flow, meteorological conditions, precipitation intermittency and moisture origin, as depicted by meteorological data, atmospheric reanalyses and Lagrangian moisture source diagnostics. These different factors can indeed alter the relationships between temperature and water stable isotopes. Using five records with sufficient resolution on the EDC3 age scale, common features are quantified through principal component analyses. Consistent with instrumental records and atmospheric model results, the ice core data depict rather coherent and homogenous patterns in East Antarctica during the last two interglacials. Across the East Antarctic plateau, regional differences, with respect to the common East Antarctic signal, appear to have similar patterns during the current and last interglacials. We identify two abrupt shifts in isotopic records during the glacial inception at TALDICE and EDML, likely caused by regional sea ice expansion. These regional differences are discussed in terms of moisture origin and in terms of past changes in local elevation histories, which are compared to ice sheet model results. Our results suggest that elevation changes may contribute significantly to inter-site differences. These elevation changes may be underestimated by current ice sheet models.

Abstract The Antarctic Ice Sheet’s reaction on the continuing global warming is crucial to project the future sea level rise. The increasing air temperature causes both accelerating mass loss on the Antarctica’s margins and increased surface mass balance in its interior. Here, we use data from firn cores drilled near Vostok station (central East Antarctica) to analyze the surface mass balance variability over the past 2200 years. We show a 24% increase of snow accumulation rate since early 19 century confirmed by the instrumental data for the last 52 years. The mean surface mass balance value in 1970–2021 (2.25 ± 0.064 g cm−2 yr−1) is very likely unprecedented in the pre-industrial era. The surface mass balance growth is accompanied by the air temperature increase with the sensitivity of 11 ± 2% per 1 °C. These results will help to constrain the potential magnitude of Antarctic snowfall mitigation of future sea level rise.

Changes in sea ice conditions and atmospheric circulation over the Southern Ocean play an important role in modulating Antarctic climate. However, observations of both sea ice and wind conditions are limited in Antarctica and the Southern Ocean, both temporally and spatially, prior to the satellite era (1970 onwards). Ice core chemistry data can be used to reconstruct changes over annual, decadal, and millennial timescales. To facilitate sea ice and wind reconstructions, the CLIVASH2k (CLimate Variability in Antarctica and the Southern Hemisphere over the past 2000 years) working group has compiled a database of two species, sodium [Na+] and sulfate [SO42-], commonly measured ionic species. The database (https://doi.org/10.5285/9E0ED16E-F2AB-4372-8DF3-FDE7E388C9A7; Thomas et al., 2022) comprises records from 105 Antarctic ice cores, containing records with a maximum age duration of 2000 years. An initial filter has been applied, based on evaluation against sea ice concentration, geopotential height (500 hPa), and surface wind fields to identify sites suitable for reconstructing past sea ice conditions, wind strength, or atmospheric circulation.

The density of the snow and firn thickness is one of the fundamental and most important physical properties of the polar ice sheets. The data on density is used for reconstructing the past snow accumulation rate variability based on firn core studies, for correcting the results of the instrumental surface mass balance measurements and for verification of empirical and physical densification models. In this work we present a unique dataset on the snow and firn density in the upper 70 m of Antarctic glacier in the vicinity of Vostok Station based on data from 32 snow pits and firn cores. This newly obtained stacked density profile reveals different stages of the densification process. In the upper 27 cm a fast growth of the density is observed from 0.320 to 0.365 g cm-3 as a result of the initial snow grain metamorphism. Below 0.3 m much slower densification rates are observed. At the depth of 22.5 m the transition from snow to firn can be seen at the density of 0.526 g cm-3. The vertical density distribution can be approximated with a polynomial function with the accuracy of 0.01 g cm-3 along the whole profile except for the upper 0.3 m. In order to investigate the glacio-climatic conditions under which the snow-firn density has evolved, we applied a semi-empirical model by Herron and Langway (1980). In first approximation, the density distribution can be explained with the initial snow density equal to 0.35 g cm-3, surface glacier temperature equal to -57 C, and snow accumulation rate of 1.8–2.1 g cm-2 yr-1. The discrepancy between the data and model can be, to our opinion, explained by the recent increase of the snow accumulation rate as evidenced from the firn core studies. However, the non-stationary physical densification model failed to reproduced the density data with sufficient accuracy, which calls for revisiting the model configuration and tuning.

Introduction: The products of volcanic eruptions found in the snow, firn and ice deposits of the polar ice sheets are precious sources of information on the volcanic forcing of the climate system in the recent or remote past. On the other hand, the layers containing the traces of well-known eruptions serve as absolute age markers that help to construct the depth-age scale for the snow-firn thickness.Methods: In this study we present new records of the sulfate concentrations and electrical conductivity (ECM) from three shallow (up to 70 m depth) firn cores drilled in the vicinity of Vostok station (central East Antarctica).Results: In the non-sea-salt sulfate and ECM profiles we were able to identify 68 peaks that can be interpreted as traces of volcanic events.Discussion: 22 of these peaks can be unambiguously attributed to well-known volcanic eruptions (including Tambora 1816 CE, Huaynaputina 1601 CE, Samalas 1258 CE, Ilopango 541 CE and others), which allowed to construct a robust depth-age scale for the cores. 37 events have their counterparts in other Antarctic cores, but cannot be associated with welldated eruptions. Finally, 9 peaks do not have analogues in the other cores, i.e., they may be traces of so far unknown volcanic events. According to the newly constructed depth-age function, the deepest studied firn layers (70.20 m) are dated by 192 BCE.

Recent studies have shown that stratigraphically disturbed meteoric ice bedded at Vostok Station between 3318 and 3539 m dates back to 1.2 Ma BP and possibly beyond. As part of the VOICE (Vostok Oldest Ice Challenge) initiative, a new deviation from parent hole 5G-1 was made at depths of 3270–3291 m in the 2018/19 austral season with the aim of obtaining a replicate core of the old ice. Sidetracking was initiated using the standard KEMS-132 electromechanical drill routinely employed for deep ice coring at Vostok, without significant changes to its initial design. Here we describe the method and operating procedures for replicate coring at a targeted depth in an existing slant hole, involving the use of a cable-suspended electromechanical drill. The design of the milling cutter head used for sidetracking is presented. The performance characteristics and the experience of drilling branch-hole 5G-5 at Vostok are described and discussed.

In this work we have presented the results of numerical modeling of the age and temperature distribution in ice layers at Dome B site (79,02° S, 93,69° E, altitude 3807 m a.s.l., ice thickness about 2.5 km), located 300 km to the west from Russian Antarctic station Vostok. Dome B is situated on the onset of the ice flow line passing through deep borehole 5G, and is considered as one of the most promising places to search for and to study the Easth’s oldest ice with the age of up to 1.5 Ma. According to our calculations, all realistic scenarios show the ice age at 60 m above the ice base to be considerably older than 1 Ma, and the glacier base temperature is well below the pressure melting point (−1.8 °С for pressure = 23 MPa). For the most likely scenario (accumulation rate 1.8 g/(cm2 year), effective ice surface temperature −64 °С and geothermal heat flux 60 mW/m2) the ice age is 1.4 Ma and the basal temperature is about −13 °С that is close to the earlier predictions from a 2D‑model. Maximum estimate of the «diffusion length» in the old ice (for the scenario in which the basal temperature reaches the melting point, and in which 30% of «excess diffusion» is taken into account) is 5.2 cm. In 1.4 Ma-old ice a 40-ka climatic cycle is squeezed into a 290-cm thick ice layer. For this ratio of wave length and diffusion length the climatic signal attenuation (ratio between the signal amplitude after and before the diffusive smoothing) is 0.6%. Thus, due to the relatively low ice temperature here we may expect a nearly undisturbed climatic curve in the old ice core that will be drilled one day at Dome B. At the same time shorter oscillations with the wavelengths of < 1500 years will be totally erased by diffusion.

Catalogues and maps of glaciers (for 2015) of Shapshal Glacier Center, located in the eastern part of the Russian Altai, have been created based on the first field glaciological observations and space images interpretation. In total 123 glaciers with the total area of 14.07 km2 have been allocated. In comparison with the data from the Glacier Inventory of the USSR (1955–1965), the total area of the glaciers has decreased by more than 2 times. The lower limit of glacier development is 2475 m, to the south-east of the region it rises by 1 km, the height of the firm line rises from 2860 m to 3460 m, respectively. Small glaciers prevail (70% of glaciers have an area less than 0.1 km2, the area of the largest glacier is 0.9 km2). In terms of quantity and area, cirque glaciers predominate, there are no valley glaciers. The largest numbers of glaciers have northern and northeastern exposure, with the largest areas of glaciers concentrated on the north-eastern slopes. The highest glaciation intensity has been detected on the eastern slope of the Skalistiy Ridge and the northeastern slope of the southern part of the Shapshalsky Ridge in the upper reaches of the Chon-Khem River, which are optimal for glaciers by a combination of mountain heights and position relative to moisture-bearing atmospheric flows. To the west of these areas, intensity of glacierization decreases due to lower mountain heights, to the east – due to lower precipitation. In general, with low (0.1 km−1 and less) intensity of glacierization, the Shapshal Centre is an area of dispersed glaciation, most glaciers of which are on the verge of disappearance.

In 2016–2017, during Russian Arctic Expedition on Svalbard (RAE‑S) we have collected the samples of atmospheric precipitation, terrestrial waters, snow and ice on Spitsbergen island in the vicinity of Grønfjorden. The measurements of stable water isotope content (δ18O and δD) in the atmospheric precipitation has allowed to draw the Local Meteoric Water Line (δD = 6,93δ18O − 0,35) and to analyze the relationship between the isotopic content and condensation temperature. Aside from this, the d-excess values in precipitation (dexc= δD − 8δ18O) was interpreted as a marker of the moisture source. It has been demonstrated that the isotopic content of the surface waters (lakes and rivers) clearly points to the dominating type of feeding (atmospheric, ground) of these hydrological objects. We have discovered the interannual variability of the isotopic composition of Lake Kongress water during 2 years and defined the sources of water in its tributes: 13 of them have atmospheric source and 9 – ground source. In general, isotopic content of water in the vicinity of Grønfjorden (mean values are: δ18O = −10,3 ‰, δD = −72,5 ‰) is higher than in other regions of Svalbard.

In this work we have presented new detailed (with the resolution of 10 cm) stable water isotope (δD and δ18O) profile measured in the central Antarctic Vostok ice core section that contains old ice with the age from 0.4 to 1.2 million years. To interpret these data we have developed a model of molecular diffusion in ice and determined the value of so-called «diffusion length». We have demonstrated that the climatic signal in this ice interval is disturbed by a combination of two processes, ice layer folding (that is accompanied by layer overturning and mixing) and molecular diffusion. The whole old ice interval can be divided in 5 zones that differ in terms of character and intensity of these two processes. In three of these zones the climatic signal is partly preserved and could be restored to some extent. However, in the most interesting and old zone 5 (0.75–1.2 Ma) the climatic signal is nearly completely erased and could hardly be reconstructed. At the same time, the isotopic records obtained from the Vostok old ice have preserved the information on the mean level of the isotopic content of ice in glacial and interglacial stages. This gives an opportunity to reveal and study long-term climatic trends with typical duration longer than main climatic cycles (40–100 ka).

The surface mass balance (SMB) is very low over the vast East Antarctic Plateau, for example in the Vostok region, where the mean SMB is on the order of 20–35 kg m-2 a-1. The observation and modeling of spatio-temporal SMB variations are equally challenging in this environment. Stake measurements carried out in the Vostok region provide SMB observations over half a century (1970–2019). This unique data set is compared with SMB estimations of the regional climate models RACMO2.3p2 (RACMO) and MAR3.11 (MAR). We focus on the SMB variations over time scales from months to decades. The comparison requires a rigorous assessment of the uncertainty in the stake observations and the spatial scale dependence of the temporal SMB variations. Our results show that RACMO estimates of annual and multi-year SMB agree well with the observations. The regression slope between modelled and observed temporal variations is close to 1.0 for this model. SMB simulations by MAR are affected by a positive bias which amounts to 6 kg m-2 a-1 at Vostok station and 2 kg m-2 a-1 along two stake profiles between Lake Vostok and Ridge B. None of the models is capable to reproduce the seasonal distributions of SMB and precipitation. Model SMB estimates are used in assessing the ice-mass balance and sea-level contribution of the Antarctic Ice Sheet by the input-output method. Our results provide insights into the uncertainty contribution of the SMB models to such assessments.

This investigation is based on measurements of stable isotopes concentrations (δD and δ18О) in water, snow and ice samples. Glaciers are composed of ice, snow, and fi n of atmospheric origin. The isotopic composition of these components is different, so when melting they form the melted glacial water with different isotope characteristics. Summer precipitation contains the heaviest isotopes, but only a small part of them remains on the glacier. The average isotopic composition of glacier ice represents the average composition of precipitation that accumulates on it. However, snow and fi n of different seasons can occur on the glacier surface, the isotopic composition of which differs from the isotopic composition of glacier ice. At different times of the ablation season different parts of the glacier melt, therefore the isotopic composition of melt waters will be different. Differences in the isotopic composition of the major runoff-forming components on the Northern slopes of the massif Tabyn-Bogdo-Ola had been identified. A part of melting ice in the formation of the runoff on this massif is determined by estimation of the isotopic composition of snow, ice, and fi n on different glaciers of this region. The average δ18О of snow on the glacier surface is −11.9‰, and this snow can be attributed to the precipitation fallen in late spring or early summer. Measured average isotopic composition of precipitation (δ18О = −11.9‰) was compared with the online calculator of the isotope content in precipitation (OIPC). The isotopic composition of glacial melt waters on the Northern macro-slope in the middle of July 2015 (δ18О = −15.3‰) differs from the isotopic composition of the territory of the Mongolian part of the massif (δ18О = −17.4‰) obtained from results of the analysis of eight samples taken at different edges of the glaciers at the beginning of August 2013. Isotopic separation shows important role of summer snow in feeding the glacial rivers of the massif even in the middle of the ablation season, especially for glaciers in the central part of the massif. The role of seasonal snow in feeding the glacier streams depends on the morphological type of glacier. It is maximum for corrie glaciers and minimum for the valley ones.

One of the key priority tasks for the international Antarctic community is drilling and studying old Antarctic ice with age exceeding 1 million years in order to investigate possible reasons for the Mid-Pleistocene Transition. During the 2017–2018 austral season at Vostok Station, we carried out microscopic study of geometrical properties of the crystalline inclusions of air hydrates in ice core samples from boreholes 5G‑3 (Vostok) and DC2 (EPICA DC) in depth intervals where the age of the ice exceeded 400,000 years. The obtained data confirmed the existence of a robust linear relationship between the mean radius of the hydrates and the age of the ice in the bottom part of the East Antarctic ice sheet, and will be useful for further development of the new dating technique based on the phenomena of hydrate growth in polar ice. Preliminary, the age of the atmospheric ice bedded at Vostok at a depth of3538 m, inferred from the data on the size of the hydrates, amounts to 1.3±0.17 million years. The existence of ice older than 1 million years in the vicinity of Vostok implies that in the area of Ridge B, where the ice flow line which passes through Vostok Station originates, even older ice, with undisturbed stratigraphy, may exist. It would be desirable therefore to carry out a glacio-geophysical traverse to Ridge B in order to implement a detailed study of Dome B area aimed at identifying the most suitable site for a new deep drilling of the Antarctic ice sheet.

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, 17O-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 17O-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.

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.

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.

The present-day global climate changes, very likely caused by anthropogenic activity, may potentially present a serious threat to the whole human civilization in a near future. In order to develop a plan of measures aimed at elimination of these threats and adaptation to these undesirable changes, one should deeply understand the mechanism of past and present (and thus, future) climatic changes of our planet. In this study we compare the present-day data of instrumental observations of the air temperature and snow accumulation rate performed in Central Antarctica (the Vostok station) with the reconstructed paleogeographic data on a variability of these parameters in the past. First of all, the Vostok station is shown to be differing from other East Antarctic stations due to relatively higher rate of warming (1.6 °C per 100 years) since 1958. At the same time, according to paleogeographic data, from the late eighteenth century to early twenty-first one the total warming amounted to about 1 °C, which is consistent with data from other Antarctic regions. So, we can make a conclusion with high probability that the 30-year period of 1985–2015 was the warmest over the last 2.5 centuries. As for the snow accumulation rate, the paleogeographic data on this contain a certain part of noise that does not allow reliable concluding. However, we found a statistically significant relationship between the rate of snow accumulation and air temperature. This means that with further rise of temperature in Central Antarctica, the rate of solid precipitation accumulation will increase there, thus partially compensating increasing of the sea level.

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.

Results of geodetic in-situ observations of ice-flow velocities in the southern part of subglacialLakeVostokare combined with data sets of the ice surface topography, ice thickness, surface accumulation, basal accretion and firn/ice density for interpretations regarding the glaciological setting of theLakeVostoksystem. Based on the ice-flow velocities and the ice thickness, mean surface accumulation rates are derived applying the flux gate method. These are representative for surface segments extending from the southern part ofLakeVostokto the Ridge B ice divide. They are consistent with the present-day accumulation rate at Vostok station and its variation upstream and thus suggest that the area has been close to steady state. In addition, ice-flow dynamics are investigated along a flow line segment extending from26 kmupstream to12 kmdownstream from Vostok station. The analysis suggests deficiencies in current modelling approaches within the transition zone from floating to grounded ice.