Since the first measurements of beryllium 10 (10Be) in ice, in the seventies, numerous profiles of this cosmogenic isotope have been obtained both in Antarctica and Greenland. In this article, we focus on Antarctic data, available at nine different sites, covering a significant part of the Holocene, from 237 to 7101 yr BP. We show that correlating their 10Be profiles allows to synchronize these ice cores with an excellent accuracy and to document the spatial variability of 10Be concentration and flux. We then examine how this variability is taken into account by a simulation of 10Be fallout recently performed with the ECHAM6.3-HAM2.3 model. Except for a systematic underestimation of 10Be fluxes at high accumulation sites, these simulations are overall very satisfying. Finally the excellent accuracy of synchronisation based on 10Be profiles allows us to derive an Antarctic stack record over the last seven millennia. The reliability of the new 10Be stack is demonstrated by its superior correspondence with the accurately dated IntCal20 record based on 14C in tree rings.

The objective was to search for microbial life in the subglacial Antarctic Lake Vostok by analyzing the natural accretion ice obtained by deep ice coring during the Russian campaign toward entering the lake. The ice samples to study originated from ice type I [1] and contained mineral inclusions. The study aimed to re-evaluate previous microbial finds obtained with Sanger sequencing using the high throughput Oxford Nanopore sequencing technology. Lake Vostok is a giant (270 x 70 km, 15800 km2 area), deep (up to 1.3km) freshwater liquid body buried in a graben beneath a 4-km thick East Antarctic Ice Sheet with the temperature near ice melting point (around -2.5oC) under 400 bar pressure. It is exceptionally oligotrophic and poor in chemical ions, under the high dissolved oxygen tension (320 – 1300 mg/L) range, with no light, and sealed from the surface biota about 15 Ma ago [1]. The common Sanger sequencing technique previously discovered thermophiles in the subglacial Lake Vostok in analyzing bacterial 16S rRNA genes [2,3,4]. The ice samples included accretion ice segments at a depth of 3561m and 3607m containing sediment inclusions. As a result, in both samples, the facultative thermophilic chemolithoautotroph Hydrogenophilus thermoluteolus of beta-Proteobacteria, which originated from hot springs, was discovered. This finding suggested that a geothermal system exists beneath the cold-water body of Lake Vostok. To clarify the presence of thermophiles in Lake Vostok, the accretion ice segments from 3607m (the thermophile mentioned above was detected here [2]), 3608m, 3607m (2 segments), and 3709m were retested by high throughput nanopore sequencing using the same genomic DNA and broader-in-cover degenerate primers for the v3-v4 region 16S rRNA genes. The nanopore controls (sham DNA isolation/negative PCR, nanopore reagents) were applied for the first time. A dozen Ma reads were obtained for all five amplicons, but only one sample, 3608, showed thermophiles in records. For this sample of 1,643,669 reads analyzed, 88% of which were classified. Amongst them, 279 (0.02%) reads were assigned to moderate thermophile Meiothermus hypogaeus NBRC 106114 (Deinococcus-Thermus), isolated from a hot spring in Japan. No reads for this find were recorded in other ice samples and controls. This could mean that a new thermophile of Deinococcus-Thermus was discovered in the native accretion ice of Lake Vostok. The Hydrogenophilus thermoluteolus remained undetected due to the use of different primers. Thus, the high throughput Oxford Nanopore sequencing technology provides a very efficient tool to record/prove the microbial content of the subglacial Antarctic water reservoirs in detail. Newly discovered meio-thermophiles might represent ingenious cell populations inhabiting faults offshore the subglacial Lake Vostok. They could provide prospects in searching for extraterrestrial thermophiles on Jupiter and Saturn's icy moons. Bulat S., Petit JR. (2023) Vostok, Subglacial Lake. In: Gargaud M. et al. (eds) Encyclopedia of Astrobiology. Springer, Berlin, Heidelberg. Pp. 3206-12 Bulat, S. et al. (2004) Int J Astrobiology 3(1), 1-12 Lavire, C. et al. (2006) Environmental Microbiology 8, 2106-14 Bulat, S. (2016) Phil Trans Royal Soc A Math Phys Eng Sci 374 (2059), 20140292

Abstract Driven by successful achievements in recovering high-resolution ice records of climate and atmospheric composition through the Late Quaternary, new ice–tephra sequences from various sites of the East Antarctic Ice Sheet (EAIS) have been studied in the last two decades spanning an age range of a few centuries to 800 kyr. The tephrostratigraphic framework for the inner EAIS, based on ash occurrence in three multi-kilometre-deep ice cores, shows that the South Sandwich Islands represent a major source for tephra, highlighting the major role in the ash dispersal played by clockwise circum-Antarctic atmospheric circulation penetrating the Antarctic continent. Tephra records from the eastern periphery of the EAIS, however, are obviously influenced by explosive activity sourced in nearby Antarctic rift provinces. These tephra inventories have provided a fundamental complement to the near-vent volcanic record, in terms of both frequency/chronology of explosive volcanism and of magma chemical evolution through time. Despite recent progress, current data are still sparse. There is a need for further tephra studies to collect data from unexplored EAIS sectors, along with extending the tephra inventory back in time. Ongoing international palaeoclimatic initiatives of ice-core drilling could represent a significant motivation for the tephra community and for Quaternary Antarctic volcanologists.

In 1980, a method was found to determine the amount of carbon dioxide in ancient air trapped in polar ice — providing direct evidence that CO 2 is coupled to climate, and affects global temperatures in the past, present and future.

Strong volcanic signals simultaneously recorded in polar ice sheets are commonly assigned to major low-latitude eruptions that dispersed large quantities of aerosols in the global atmosphere with the potential of inducing climate perturbations. Parent eruptions responsible for specific events are typically deduced from matching to a known volcanic eruption having coincidental date. However, more robust source linkage can be achieved only through geochemical characterisation of the airborne volcanic glass products (tephra) sometimes preserved in the polar strata. We analysed fine-grained tephra particles extracted from layers of the AD 1259 major bipolar volcanic signal in four East Antarctic ice cores drilled in different widely-spaced locations on the Antarctic Plateau. The very large database of glass-shard geochemistry combined with grain size analyses consistently indicate that the material was sourced from multiple distinct eruptions. These are the AD 1257 mega-eruption of Samalas volcano in Indonesia, recently proposed to be the single event responsible for the polar signal, as well as a newly-identified Antarctic eruption, which occurred in northern Victoria Land in AD 1259. Finally, a further eruption that took place somewhere outside of Antarctica has also contributed to tephra deposition. Our high-resolution, multiple-site approach was critical for revealing spatial heterogeneity of tephra at the continental scale. Evidence from ice-core tephra indicates recurrent explosive activity at the Antarctic volcanoes and could have implications for improved reconstruction of post-volcanic effects on climate from proxy polar records.

More than 2,000 analyses of beryllium‐10 (10Be) and sulphate concentrations were performed at a nominal subannual resolution on an ice core covering the last millennium as well as on shorter records from three sites in Antarctica (Dome C, South Pole, and Vostok) to better understand the increase in 10Be deposition during stratospheric volcanic eruptions. A significant increase in 10Be concentration is observed in 14 of the 26 volcanic events studied. The slope and intercept of the linear regression between 10Be and sulphate concentrations provide different and complementary information. Slope is an indicator of the efficiency of the draining of 10Be atoms by volcanic aerosols depending on the amount of sulphur dioxide (SO2) released and on the altitude it reaches in the stratosphere. The intercept provides an appreciation of the 10Be production in the stratospheric reservoir, ultimately depending on solar modulation (Baroni et al., 2019, JGR). Among all the identified events, the Samalas event (1257 CE) stands out as the biggest eruption of the last millennium with the lowest positive slope. It released (158 ± 12) Tg of SO2 up to an altitude of 43 km in the stratosphere (Lavigne et al., 2013, PNAS ; Vidal et al., 2016, Sci. Rep.). We hypothesize that the persistence of volcanic aerosols in the stratosphere after the Samalas eruption has drained the stratospheric 10Be reservoir for a decade. The persistence of Samalas sulphate aerosols might be due to the increase of SO2 lifetime because of: (i) the exhaustion of the OH reservoir required for sulphate formation (e.g. (Bekki, 1995, GRL; Bekki et al., 1996, GRL; Savarino et al., 2003, JGR); and/or, (ii) the evaporation followed by photolysis of gaseous sulphuric acid back to SO2 at altitudes higher than 30 km (Delaygue et al., 2015, Tellus; Rinsland et al., 1995, GRL). In addition, the lifetime of air masses increases to 5 years above 30 km altitude compared with 1 year for aerosols and air masses in the lower stratosphere (Delaygue et al., 2015, Tellus). When this high-altitude SO2 finally returns below the 30 km limit, it could be oxidized back to sulphate and forms new sulphate aerosols. These processes could imply that the 10Be reservoir is washed out over a long time period following the end of the eruption of Samalas. This would run counter to modelling studies that predict the formation of large particle sizes and their rapid fall out due to the large amount of SO2, which would limit the climatic impact of Samalas-type eruptions (Pinto et al., 1989, JGR; Timmreck et al., 2010, 2009, GRL).

AbstractWe analyzed the single‐grain mineralogical composition of aeolian dust transported to central East Antarctica for provenance purposes. Comparison with data from the last glacial period shows for the first time disappearance of carbonates during the Holocene related to sea level rise and suppressed deflation from the Argentinean continental shelf, exposed during Marine Isotope Stage 2. Zeolites, related to alteration of volcanic glass in the subglacial/periglacial environment of Patagonia, show a similar behavior. The remaining minerals, remarkably similar between the two climatic periods, are compatible with a Pampean and Patagonian provenance, but Holocene data show a more pronounced volcanic and metamorphic imprint and presence of minerals related to warm climate weathering environments compatible with an additional contribution from subtropical latitudes of South America. These results do not imply a major large‐scale reorganization of atmospheric circulation after the last climatic transition.

We analyzed helium and neon in 24 samples from between 3,607 and 3,767m (i.e., down to 2m above the lake-ice interface) of the accreted ice frozen to the ceiling of Lake Vostok. Within uncertainties, the neon budget of the lake is balanced, the neon supplied to the lake by the melting of glacier ice being compensated by the neon exported by lake ice. The helium concentration in the lake is about 12 times more than in the glacier ice, with a measured He-3/He-4 ratio of 0.120.01R(a). This shows that Lake Vostok's waters are enriched by a terrigenic helium source. The He-3/He-4 isotope ratio of this helium source was determined. Its radiogenic value (0.057xR(a)) is typical of an old continental province, ruling out any magmatic activity associated with the tectonic structure of the lake. It corresponds to a low geothermal heat flow estimated at 51mW/m(2). Plain Language Summary Extending over 15,000km(2) in a deep trough north of Vostok station, Lake Vostok is the largest and the deepest among the many subglacial lakes to have been discovered in Antarctica. Its ice ceiling is tilted, with an ice thickness of 3,750m in the south and 4,300m in the north. As the melting point is pressure dependent, the base of the glacier melts on the thick side (northern region) whereas lake water refreezes in the south, where the Vostok station is located. Unlike most gases, helium and neon can be incorporated into the crystal structure of ice during freezing. This property makes helium and neon isotopes in the accreted ice a valuable source of information on the concentration and isotope composition of both gases in the lake water itself. Between 2006 and 2012, we collected 24 samples from between 3,607 and 3,767m (i.e., down to 2m above the lake-ice interface) of the accreted ice frozen to the ceiling of Lake Vostok (lake ice) for analyzing helium and neon. Within uncertainties, the neon concentration measured in the lake ice is equal to that in the glacier ice. This indicates that the neon budget of the lake is balanced, the neon supply to the lake by the melting of glacier ice being compensated by the Ne export by lake ice. This confirms earlier suggestions from radar data and GPS measurements of surface ice velocity that the water added to the lake by the melting of glacier ice is balanced by the lake ice, which is exported by the glacier's movement out of the lake. Helium isotopes (He-3 and He-4) are sensitive indicators of tectonic-magmatic activity. In continental areas of recent tectonic-magmatic activity such as geothermal areas, the ratio He-3/He-4 is at its highest, accompanied by excess heat flow. On the contrary, in stable continental areas, low He-3/He-4 ratios are found. The low He-3/He-4 ratio in Lake Vostok clearly demonstrates the absence of volcanic and/or magmatic activity associated with the tectonic structure of the lake, in agreement with the absence of magnetic anomaly. The helium concentration in the lake is about 12 times the concentration measured in the glacier ice. This shows that the Lake Vostok's waters are enriched from beneath by a flux of helium typical of an old stable continental province. Helium isotopes points to a low geothermal heat flow beneath the lake. We estimate this heat flow at 51mW/m(2). This value is fully consistent with the heat flow map for Antarctica inferred from satellite magnetic data and corresponds to the baseline heat flow in Antarctica. Our data do not allow us to determine the helium flux and the residence time of the lake waters independently, but only as the product of these two quantities. If we adopt the previously determined residence time of 13,300years based on geophysical inferences, we note that the helium flux value is close to the maximum of the lognormal distribution of continental helium fluxes, corresponding to the maximum likelihood of the continental helium flux.

Ice core records from Antarctica show mostly synchronous temperature variations during the last deglacial transition, an indication that the climate of the entire continent reacted as one unit to the global changes. However, a record from the Taylor Dome ice core in the Ross Sea sector of East Antarctica has been suggested to show a rapid warming, similar in style and synchronous with the Oldest Dryas—Bølling warming in Greenland. Since publication of the Taylor Dome record, a number of lines of evidence have suggested that this interpretation is incorrect and reflects errors in the underlying time scale. The issues raised regarding the dating of Taylor Dome currently linger unresolved, and the original time scale remains the de facto chronology. We present new water isotope and chemistry data from nearby Taylor Glacier to resolve the confusion surrounding the Taylor Dome time scale. We find that the Taylor Glacier record is incompatible with the original interpretation of the Taylor Dome ice core, showing that the warming in the area was gradual and started at ∼18 ka BP (before 1950) as seen in other East Antarctic ice cores. We build a consistent, up‐to‐date Taylor Dome chronology from 0 to 60 ka BP by combining new and old age markers based on synchronization to other ice core records. The most notable feature of the new TD2015 time scale is a gas age—ice age difference of up to 12,000 years during the Last Glacial Maximum, by far the largest ever observed.

Comparative analysis of the Vostok ice core (Central East Antarctica; one horizon, three boreholes) and D10 ice core (shoreline nearby the French Dumont d'Urville station) has reliably revealed three phylotypes (species) of aerobic iron-oxidizing betaproteobacteria of the family Gallionellaceae (closely related at the genus level to Sideroxydans lithotrophicus and Ferriphaselus amnicola), one of which has been detected from both the Vostok (borehole 5G-3) and D10 cores. In addition, the phylotype related to sulfur-oxidizing bacteria Tumebacillus sp. has been detected from both the Vostok (borehole 5G-2) and D10 cores. The both ice cores are almost equal in age, about 20000 years; however, they differ in origin: the ice from Dumont d'Urville is atmospheric, while that from Vostok is a lake ice. The ice samples greatly vary in the storage time before treatment in the laboratory (from 0.5 to 40 years) and in intervals between treatments (from 1 to 5 years). The drilling sites are more than 1000 km apart. No evident hydrological links (the transfer of water beneath the ice sheet) between the Lake Vostok and Dumont D'Urville station have been found. This coincidence can be explained by the fact that minerals from the bedrock under the glacier, containing ferrous iron and reduced sulfur compounds, as well as physical and chemical conditions in both sites, liquid fresh water at a temperature near the freezing point, are similar. These and other assumptions are considered in the present article.

Better assessing the dynamic of stratosphere‐troposphere exchange is a key point to improve our understanding of the climate dynamic in the East Antarctica Plateau, a region where stratospheric inputs are expected to be important. Although tritium (3H or T), a nuclide naturally produced mainly in the stratosphere and rapidly entering the water cycle as HTO, seems a first‐rate tracer to study these processes, tritium data are very sparse in this region. We present the first high‐resolution measurements of tritium concentration over the last 50 years in three snow pits drilled at the Vostok station. Natural variability of the tritium records reveals two prominent frequencies, one at about 10 years (to be related to the solar Schwabe cycles) and the other one at a shorter periodicity: despite dating uncertainty at this short scale, a good correlation is observed between 3H and Na+ and an anticorrelation between 3H and δ18O measured on an individual pit. The outputs from the LMDZ Atmospheric General Circulation Model including stable water isotopes and tritium show the same 3H‐δ18O anticorrelation and allow further investigation on the associated mechanism. At the interannual scale, the modeled 3H variability matches well with the Southern Annular Mode index. At the seasonal scale, we show that modeled stratospheric tritium inputs in the troposphere are favored in winter cold and dry conditions.

Polar ice cores are unique climate archives. Indeed, most of them have a continuous stratigraphy and present high temporal resolution of many climate variables in a single archive. While water isotopic records (δD or δ18O) in ice cores are often taken as references for past atmospheric temperature variations, their relationship to temperature is associated with a large uncertainty. Several reasons are invoked to explain the limitation of such an approach; in particular, post-deposition effects are important in East Antarctica because of the low accumulation rates. The strong influence of post-deposition processes highlights the need for surface polar research programs in addition to deep drilling programs. We present here new results on water isotopes from several recent surface programs, mostly over East Antarctica. Together with previously published data, the new data presented in this study have several implications for the climatic reconstructions based on ice core isotopic data: (1) The spatial relationship between surface mean temperature and mean snow isotopic composition over the first meters in depth can be explained quite straightforwardly using simple isotopic models tuned to d-excess vs. δ18O evolution in transects on the East Antarctic sector. The observed spatial slopes are significantly higher (∼ 0.7–0.8‰·°C−1 for δ18O vs. temperature) than seasonal slopes inferred from precipitation data at Vostok and Dome C (0.35 to 0.46‰·°C−1). We explain these differences by changes in condensation versus surface temperature between summer and winter in the central East Antarctic plateau, where the inversion layer vanishes in summer. (2) Post-deposition effects linked to exchanges between the snow surface and the atmospheric water vapor lead to an evolution of δ18O in the surface snow, even in the absence of any precipitation event. This evolution preserves the positive correlation between the δ18O of snow and surface temperature, but is associated with a much slower δ18O-vs-temperature slope than the slope observed in the seasonal precipitation. (3) Post-deposition effects clearly limit the archiving of high-resolution (seasonal) climatic variability in the polar snow, but we suggest that sites with an accumulation rate of the order of 40 kg.m−2.yr−1 may record a seasonal cycle at shallow depths.

Tephra isochrons offer considerable potential for correlating diverse palaeoarchives and highlighting regional climatic differences. They are especially useful when applied to polar ice records encompassing the last glacial, as these clearly portray the pronounced millennial-scale climate variability that characterised this period. Here we present the continuous record of primary fallout tephra layers in the East Antarctic Talos Dome ice core (72°49′S, 159°11′E), developed upon examination of the core sections spanning the glacial period 16.5 to 71 ka. A total of ca. 45 discrete tephra deposits precisely positioned stratigraphically relative to the temperature record for the core and dated using the AICC2012 timescale, were identified. Quantitative grain size, particle morphology, major and trace element composition using Coulter Counter, SEM, EPMA-WDS, and LA-ICP-MS analytical methods were studied as diagnostic features for tephra characterisation. The tephrostratigraphic framework provides a reference for future precise comparison between ice and sediment sequences across the Antarctic continent. Indeed, several potential markers characterised by distinct volcanic glass geochemistry and/or particular stratigraphic location (e.g., a 17.6-ka ash layer deposited during the well-known major acidity event) are now available for the direct linkage of palaeoclimatic archives. The Talos Dome tephra sequence, dominated by mid-distal pyroclastic products from the nearby Northern Victoria Land volcanoes, also represents the most comprehensive and best time-constrained record of regional Antarctic volcanism yet developed. It documents nearly continuous sustained explosive activity during the considered time interval and, combined with previous ice-core tephra results for the last and the current interglacial periods, suggests progressive compositional shift through time.

We here investigate the spatial and temporal variability of eolian dust particle sorting recorded in the Dome B (77° 05′ S, 94° 55' E) ice core, central East Antarctica, during Marine Isotope Stage (MIS) 2. We address the question whether such changes reflect variable transport pathways from a unique source area or rather a variable apportionment from diverse Southern Hemisphere sources transported at different elevation in the troposphere. The Sr-Nd radiogenic isotope composition of glacial dust samples as well as single-particle Raman mineralogy support the hypothesis of a single dust provenance both for coarse and fine mode dust events at Dome B. The southern South American provenance of glacial dust in Antarctica deduced from these results indicate a dust composition coherent with a mixture of volcanic material and minerals derived from metamorphic and plutonic rocks. Additionally, Dome B glacial samples contain aragonite particles along with diatom valves of marine benthic/epiphytic species and freshwater species living today in the northern Antarctic Peninsula and southern South America. These data suggest contribution from the exposed Patagonian continental shelf and glacial outwash plains of southern Patagonia at the time when sea level reached its minimum. Our results confirm that dust sorting is controlled by the relative intensity of the two main patterns of tropospheric dust transport onto the inner Plateau, i.e. fast low-level advection and long-range high-altitude transport including air subsidence over Antarctica.

Using new high-resolution 10Be measurements in the NGRIP, EDML and Vostok ice cores, together with previously published data from EDC, we present an improved synchronization between Greenland and Antarctic ice cores during the Laschamp geomagnetic excursion ∼ 41 kyr ago. We estimate the precision of this synchronization to be ±20 years, an order of magnitude better than previous work. We discuss the implications of this new synchronization for making improved estimates of the depth difference between ice and enclosed gas of the same age (Δdepth), difference between age of ice and enclosed gas at the same depth (Δage) in the EDC and EDML ice cores, spectral properties of the 10Be profiles and phasing between Dansgaard–Oeschger-10 (in NGRIP) and AIM-10 (in EDML and EDC).