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Abstract

Based on the results of geochemical and glaciological investigations in snow pits and shallow cores, regional stack series of air temperature in central Antarctica (in the southern part of Vostok Subglacial Lake) were obtained, covering the last 350 years. It is shown that this parameter varied quasi-periodically with a wavelength of 30–50 years. The correlation of the newly obtained record with the circulation indices of the Southern Hemisphere (SH) shows that the central Antarctic climate is mainly governed by the type of circulation in the SH: under conditions of zonal circulation, negative anomalies of temperature and precipitation rate are observed, whereas the sign of the anomalies is positive during meridional circulation. In the 1970s the sign of the relationship between many climatic parameters changed, which is likely related to the rearrangement of the climatic system of the SH. The data suggest that during the past 350 years such events have taken place at least five times. The stable water isotope content of the central Antarctic snow is governed by the summer temperature rather than the mean annual temperature, which is interpreted as the influence of 'post-depositional' effects.

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... The chemical and physical signals measured in an individual ice core reflect a local climatic signal archived through the deposition and reworking of snow layers. The intermittency of Antarctic precipitation ( Masson-Delmotte et al., 2011;Sime et al., 2009), variability in precipitation source regions ( Sodemann and Stohl, 2009), and post-depositional effects of snow layers including wind drift and scouring, sublimation, and snow metamorphism ( Frezzotti et al., 2007;Ekaykin et al., 2014;Touzeau et al., 2016;Casado et al., 2016;Hoshina et al., 2014;Steen-Larsen et al., 2014) can distort the climate signal preserved within ice cores and produces non-climatic noise. As a result, obtaining a robust climate signal can only be achieved through the combination of multiple ice core records from a given site and/or region, and through the site-specific calibration of the relationships between water stable isotopes and temperature. ...
... Most of the records have a data resolution ranging from 0.025 to 5 years (only three records have a resolution of > 10 years). Previous studies ( Frezzotti et al., 2007;Ekaykin et al., 2014) have shown that post-depositional and wind scouring effects, acting more effectively when the accumulation rate is very low, limit our ability to obtain temperature reconstructions at annual resolution in most of the interior of Antarctica. Because of this, in our regional reconstructions we use 5-year-averaged data for reconstructing the last 200 years, and 10-year averages for reconstructing the last 2000 years. ...
... This reduction in resolution is designed to reduce the influence of small age uncertainties between the records, as well as the non-climatic noise induced by post-deposition (e.g. wind erosion, diffusion) processes ( Frezzotti et al., 2007;Ekaykin et al., 2014). The 5-year resolution records were converted to anomalies relative to their mean over the 1960-1990 CE interval, and records that do not include a minimum of six bins (30 years) of coverage since 1800 CE are excluded based on length. ...
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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.
... This archive is particularly useful in the southern hemisphere, where continental archives are rare (Mann and Jones, 2003;Mayewski and Goodwin, 1999). In Antarctica, where meteorological records only started in the 50's (Genthon et al., 2013), these archives are not only a tool for past climate reconstruction, but also a necessary source of information for understanding climate variability (Ekaykin et al., 2014;EPICA comm. members, 2006;Jouzel et al., 2007;Jouzel et al., 2005;Masson-Delmotte et al., 2003;Shaheen et al., 2013;Steig, 2006;Stenni et al., 2011;35 Stenni et al., 2004) and recent climate change (Altnau et al., 2015;Joos and Spahni, 2008;Mann and Jones, 2003;Mayewski and Goodwin, 1999;Schneider et al., 2006). ...
... In addition, uneven accumulation in time and space introduces randomness in the core stratigraphy ('stratigraphic noise', Ekaykin et al., 2009). Indeed, records from adjacent snow pits have been shown to be markedly different, under the influence of decameter-scale local effects (wind redeposition of snow, erosion, compaction, metamorphism) (Casado et al., 2016b;Ekaykin et al., 2014;Ekaykin et al., 2002;Petit et al., 1982). ...
... These local effects reduce the signal /noise ratio, and then only stacking a series of snow pits can eliminate this local 45 variability and yield information relevant to recent climate variations (Altnau et al., 2015;Ekaykin et al., 2014;Ekaykin et al., 2002;Fisher and Koerner, 1994;Hoshina et al., 2014). This concern is particularly significant in central regions of east Antarctica characterized by very low accumulation rates (< 100 mm w.e. per year, van de Berg et al., 2006) and strong winds which can scour and erode snow layer over depths larger than the annual accumulation (Frezzotti et al., 2005;Libois et al., Geosci. ...
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To evaluate the impact of vapor diffusion onto isotopic composition variations in the snow pits and then in ice cores, we introduced water isotopes in the detailed snowpack model Crocus. The isotopes routine is run with a 1 s resolution. At each step and for each snow layer, 1) the initial isotopic composition of vapor is taken at equilibrium with solid phase, 2) kinetic fractionation is applied during transport, and 3) condensation is realized. We study the different effects of temperature gradient, compaction, wind compaction and precipitation on the final vertical isotopic profiles. We also run complete simulations of vapor and isotopic diffusion at GRIP, Greenland and at Dome C, Antarctica over periods of 1 or 10 years. The vapor diffusion tends to smooth the original seasonal signal, with an attenuation of 9.5 % of the original signal over 10 years at GRIP. This is smaller than the observed attenuation in ice cores, indicating that the model underestimates attenuation due to diffusion or that other processes, such as ventilation, also contribute to the observed attenuation. At Dome C, the attenuation is stronger (14 %), probably because of the lower accumulation and stronger δ¹⁸O gradients. Because vapor diffusion is not the only process responsible of the signal attenuation, it would be useful to implement in the model ventilation of the snowpack and exchanges with the atmosphere to evaluate their contribution.
... Despite limitations by diffusion, water isotopes in snow pits and shallow ice cores are still largely used for the reconstruction of recent climate variations (Altnau et al., 2014;Goursaud et al., 2016;Jouzel et al., 1983;Kü ttel et al., 2012;Schneider et al., 2006). For sites characterized by low accumulation rate, stacking several pits enables one to increase the ratio between signal and noise, hence improving the climatic reconstruction (Ekaykin et al., 2014;Mü nch et al., 2015). ...
... We finally stress here the large dispersion between d 18 O records from the same site (e.g., for Vostok and Dome C). This confirms the strong spatial variability already observed on records of impurities, densities and isotopes from different snow pits drilled the same year, but at distances of several tenths of meters (Ekaykin et al., 2014;Gautier et al., 2016;Hoshina et al., 2016;Laepple et al., 2016;Libois et al., 2014;Mü nch et al., 2015). Intermittency of precipitation, sublimation of snow, deposition and post-deposition effects (e.g., firn ventilation, diffusion and blowing snow) are good candidates for explaining the lack of seasonal record archived in snow pits. ...
... Post-deposition effects clearly limit the possible archiving of high-resolution (seasonal) climatic variability in the polar snow. Earlier studies suggested that seasonal cycles could not be recorded in snow water isotopes from low accumulation rate sites of East Antarctica (Ekaykin et al., 2014). Using new isotopic records from snow pits drilled in high-accumulation and low-accumulation sites of East Antarctica, we are able to adjust/refine this statement. ...
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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.
... In our previous work we summarized available isotopic data for the vicinity of Vostok Station in order to construct a robust 10 stack climatic record over the past 350 years (Ekaykin et al., 2014). Here we present a new stacked climate record for Princess Elisabeth Land (PEL), the territory located between the Russian stations of Progress, Vostok and Mirny, East Antarctica. ...
... Note that all spectral analyses and filtering was performed with the use of Analyseries software (Paillard et al., 1996). This is motivated by the fact that onesingle record in inland Antarctica cannot provide reliable climatic information on a short-term time scale, due to a very low signal-to-nose ratio (Ekaykin et al., 2014). Moreover, the latter study also highlighted multi-decadal climatic variability in this sector of central Antarctica, with a period of 30-50 years. ...
... IPO index is closely related to PDO (Pacific Decadal Oscillation), but PDO better characterizes Northern Pacific, while IPO is better applicable to the whole Pacific region. We use IPO data because in the previous study a 10 teleconnection between PDO mode and central Antarctic climate was discovered (Ekaykin et al., 2014). Here, we first consider the variability of surface air temperature recorded at the meteorological stations in Princess Elisabeth ...
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We use isotopic composition (δD) data from 6 sites in Princess Elisabeth Land (PEL) in order to reconstruct the air temperature variability in this sector of East Antarctica for the last 350 years. First, we use the present-day instrumental mean annual surface air temperature data to demonstrate that the studied region (between Russian research stations Progress, Vostok and Mirny) is characterized by uniform temperature variability. We thus construct the stacked record of the temperature anomaly for the whole sector for the period 1958–2015. A comparison of this series with the Southern Hemisphere climatic indices shows that the short-term inter-annual temperature variability is primarily governed by Antarctic Oscillation (AAO) and Interdecadal Pacific Oscillation (IPO) modes of atmospheric variability. However, the low-frequency temperature variability (with period > 27 years) is mainly related to the anomalies of Indian Ocean Dipole (IOD) mode. Then we construct the stacked record of δD for the PEL for the period 1654–2009 from individual normalized and filtered isotopic records obtained at 6 different sites ('PEL2016' stacked record). We use a significant relationship between this record and the stacked PEL temperature record (with an apparent slope of 9 ‰ °C−1) to convert 'PEL2016' into temperature scale. Analysis of 'PEL2016' shows a 1 °C warming in this region over the last three centuries, with a particularly cold period from mid-18th to mid-19th century. A peak of cooling occurred in the 1840s – a feature previously observed in other Antarctic records. We reveal that 'PEL2016' correlates with a low-frequency component of IOD. We suggest that the IOD mode influences the Antarctic climate by modulating the activity of cyclones that bring heat and moisture to Antarctica. We also compare 'PEL2016' with other Antarctic stacked isotopic records. This work is a contribution to PAGES and IPICS Antarctica 2k projects.
... The strong post-depositional metamorphosis of snow in the megadunes has to modify its stable water isotope properties (Courville et al., 2007;Frezzotti et al., 2002b;Neumann et al., 2005). It is also known that irregular snow redistribution by wind due to complex surface topography does affect the isotopic content of the deposited snow, which causes a poor correlation of isotopic profiles obtained at two points, separated only by a short distance (Ekaykin et al., 2014;Benoist et al., 1982;Karlöf et al., 2006). However, no systematic study of snow isotopic composition in the megadunes has been conducted up to now. ...
... 3a and eby the above-mentioned velocity of the dune drift. We also showed the climatic variability in the Vostok region over the same time interval (Ekaykin et al., 2014) inFig. 5ain purple. ...
... 3aand e and data on the dune drift velocity. Purple shows climatic variability of the snow isotopic composition in the Vostok region taken from (Ekaykin et al., 2014). (b) A combination of climatic and dune-related isotopic variability (red and purple from(b) and depth–age function (c), in red, compared with the real vertical profile of snow isotopic composition measured in the core drilled in point MD00, in blue. ...
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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
... The strong post-depositional metamorphosis of snow in the megadunes has to modify its stable water isotope properties (Courville et al., 2007; Frezzotti et al., 2002b; Neumann et al., 2005 ). It is also known that irregular snow redistribution by wind due to complex surface topography does affect the isotopic content of the deposited snow, which causes a poor correlation of isotopic profiles obtained at two points, separated only by a short distance (Ekaykin et al., 2014; Benoist et al., 1982; Karlöf et al., 2006 ). However, no systematic study of snow isotopic composition in the megadunes has been conducted up to now. ...
... To construct these curves, we simply divided the distance of each point in Fig. 3a and eby the above-mentioned velocity of the dune drift. We also showed the climatic variability in the Vostok region over the same time interval (Ekaykin et al., 2014) in Fig. 5a in purple. Note that the amplitudes of the both components are similar. ...
... To calculate this we used the data from Fig. 3aand e and data on the dune drift velocity. Purple shows climatic variability of the snow isotopic composition in the Vostok region taken from (Ekaykin et al., 2014). (b) A combination of climatic and dune-related isotopic variability (red and purple from (b) and depth–age function (c), in red, compared with the real vertical profile of snow isotopic composition measured in the core drilled in point MD00, in blue. ...
Article
Full-text available
We present the results of glaciological investigations in the mega-dune area located 30 km to the east from Vostok Station (central East Antarctica) implemented during the 58th, 59th and 60th Russian Antarctic Expedition (January 2013–January 2015). Snow accumulation rate and isotope content (δD, δ18O and δ17O) were measured along the 2 km profile across the mega-dune ridge accompanied by precise GPS altitude measurements and 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 one order of magnitude within the distance
... In addition, uneven ac- cumulation in time and space introduces stratigraphic noise ( Ekaykin et al., 2009). Records from adjacent snow pits have been shown to be markedly different under the influence of decameter-scale local effects such as wind redeposition of snow, erosion, compaction, and metamorphism (Ekaykin et al., 2014;Petit et al., 1982). These local effects reduce the signal to noise ratio. ...
... These local effects reduce the signal to noise ratio. Then only stacking a series of records from snow pits can eliminate this local variability and yield information relevant to recent climate variations (Fisher and Koerner, 1994;Hoshina et al., 2014;Ekaykin et al., 2014;Altnau et al., 2015). This concern is particularly significant in the central regions of East Antarctica characterized by ac- cumulation rates lower than 100 mm of water equivalent per year (van de Berg et al., 2006). ...
Article
Full-text available
To evaluate the impact of vapor diffusion on isotopic composition variations in snow pits and then in ice cores, we introduced water isotopes in the detailed snowpack model Crocus. At each step and for each snow layer, (1) the initial isotopic composition of vapor is taken at equilibrium with the solid phase, (2) a kinetic fractionation is applied during transport, and (3) vapor is condensed or snow is sublimated to compensate for deviation to vapor pressure at saturation. We study the different effects of temperature gradient, compaction, wind compaction, and precipitation on the final vertical isotopic profiles. We also run complete simulations of vapor diffusion along isotopic gradients and of vapor diffusion driven by temperature gradients at GRIP, Greenland and at Dome C, Antarctica over periods of 1 or 10 years. The vapor diffusion tends to smooth the original seasonal signal, with an attenuation of 7 to 12ĝ€% of the original signal over 10 years at GRIP. This is smaller than the observed attenuation in ice cores, indicating that the model attenuation due to diffusion is underestimated or that other processes, such as ventilation, influence attenuation. At Dome C, the attenuation is stronger (18ĝ€%), probably because of the lower accumulation and stronger 18O gradients.
... Одна из причин этого, возможно, неточность датировки, но даже если для расчётов использовать скользящие средние значения изо топного состава и изменить датировку на ±1 год, то значение коэффициента корреляции суще ственно не изменится . Другое возможное объяс нение этого явления -перестройка климатиче ской системы, которая происходила в 1970-80х годах, примеры которой часто встречаются в на учной литературе [20,22,30] . Такая перестройка могла изменить места формирования воздушных масс, приносящих осадки на Эльбрус, траектории их движения, а также соотношения осадков, вы падающих из разных типов воздушных масс . ...
... Корреляции между климатическими характеристиками (коэффициенты значимые с p < несколько выше, чем при сравнении со средней за сезон температу рой воздуха . Таким образом, выполнение ре конструкции температуры воздуха с помощью простого уравнения регрессии на Кавказе невоз можно, хотя этот метод часто применяется в по лярных регионах (см ., например,[20]) . Рис. 6. Пример расчёта обратных траекторий движения воздушных масс по модели FLEXPART: а -июль 2012 г .; б -декабрь 2011 г . ...
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The results of the isotopic investigations of several ice cores obtained at the Western Plateau of Mt. Elbrus (the Caucasus) are presented. There is a distinct seasonal cycle in the isotopic composition record in these cores. Mean annual and seasonal values of the isotopic composition and accumulation rate were reconstructed for 89 years (1924–2012). These values were compared with the available regional meteorological data and the atmospheric circulation characteristics. It was shown that in the summer season the isotopic composition reflects the local temperature while in winter it depends on the atmospheric circulation.
... The climate information derived from the phenological records and historical winter snow-day records in East Asia region mainly reflect the early-spring and winter temperatures, respectively (Ge et al., 2003;Aono and Kazui, 2008). Another example is recently pointed out by Ekaykin et al. (2014) where these authors convincingly demonstrated that their stacked δD isotopic proxy record for the past three centuries from Vostok station in East Antarctica best represented summer temperature variations and that summer-sensitive proxy behavior is distinctly different from variations in annual-mean temperature (Ekaykin et al., 2014). The synthesis of these climate records may result in substantial uncertainty if the seasonal cycle amplitude is large (i.e., especially over mid-to-high latitude regions; including even highly sensitive tropical regions like northern SCS described above) and that seasonal bias is a significant factor for the proxies. ...
... The climate information derived from the phenological records and historical winter snow-day records in East Asia region mainly reflect the early-spring and winter temperatures, respectively (Ge et al., 2003;Aono and Kazui, 2008). Another example is recently pointed out by Ekaykin et al. (2014) where these authors convincingly demonstrated that their stacked δD isotopic proxy record for the past three centuries from Vostok station in East Antarctica best represented summer temperature variations and that summer-sensitive proxy behavior is distinctly different from variations in annual-mean temperature (Ekaykin et al., 2014). The synthesis of these climate records may result in substantial uncertainty if the seasonal cycle amplitude is large (i.e., especially over mid-to-high latitude regions; including even highly sensitive tropical regions like northern SCS described above) and that seasonal bias is a significant factor for the proxies. ...
Article
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High-resolution late Holocene climate records that can resolve seasonality are essential for confirming past climatic dynamics, understanding the late 20th century global warming and predicting future climate. Here a new composite record of the sea surface temperature, SST, variation in the northern South China Sea (SCS) during the late Holocene is constructed by combining seven seasonally-resolved coral and Tridacna gigas Sr/Ca-based SST time-windows with the instrumental SST record from modern interval between 1990 and 2000. This composite multi-proxy marine record, together with the reconstructions from mainland China and tropical Western Pacific, indicates that the late Holocene warm periods, the Roman Warm Period (RWP) and Medieval Warm Period (MWP), were prominently imprinted and documented in the climatic and environmental history of the East Asia–Western Pacific region. Meanwhile, substantial and significant SST seasonality variations during the late Holocene were observed in the composite record. The observed increase in seasonality (or amplitude of seasonal cycles) during the cold periods around our study area was probably caused by the different amplitudes between winter versus summer SST variations in northern SCS, with much larger SST variation during winters than during summers for the late Holocene. In addition, the distinctive warm, cold and neutral climatic episodes identified in our northern SCS composite SST record correspond well with other paleo reconstructions from mainland China and especially well with the Northern Hemisphere-wide composites by Moberg et al. (2005) and Ljungqvist (2010). The overall agreement however also calls for more information and insights on how seasonal temperatures and their ranges vary on decadal–centennial timescales.
... At the first stage we determine the position of Tambora volcanic peak (eruption in 1815 and the deposition of the eruption products in central Antarctica in 1816; note that the volcanic sulfates usually reach central Antarctica 1-3 years after the eruption, and in this paper we refer to the dates of the sulfate deposition rather than to the dates of the eruptions themselves). The identification of Tambora peak is absolutely unambiguous because of its specific double summit shape (Tambora itself and an unknown volcanic event dated by 1809 CE) and due to the fact that Tambora have been previously found in all the deep pits and firn cores studied in the vicinity of Vostok (Legrand, 1987;Ekaykin et al., 2004;Ekaykin et al., 2014;Osipov et al., 2014;Veres et al., 2020), so the expected depth of the peak is well known. In the VK16 sulfate record it is situated at the depths 10.39-10.56 ...
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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.
... Traces of Pinatubo eruptions have been found in various regions of Antarctica (Cole-Dai et al., 1997;Osipov et al., 2014), which indicates there is good coherence of volcanic sulphate spatially. In addition, the presence of long-distance links between the Vostok station area and low latitudes was corroborated by the correlations between the content of stable isotopes or sodium time series and tropical atmospheric circulation indices (Lazarenkov et al., 2011;Ekaykin et al., 2014;Osipov et al., 2017). The principal component analysis (PCA) showed (Tables 4 and 5) that in VK-55, the maximal variability (PC1 accounted for 33 %) was associated with SO 4 2− , H + , and Na + . ...
Article
In this study, by using ion chromatography, we analyzed the chemical composition of snow deposited in 1976–2012 at three sites within the Indian Ocean sector of East Antarctica (VK-55, SW-42, and PV-10) to establish the relationships between the formation of the chemical composition of snow and varying mechanisms of atmospheric circulation. Dating of samples was carried out on the basis of sulphate peaks related to the material derived from the Pinatubo volcanic eruption (1991). Chemical compositions of snow showed spatial inhomogeneity even over relatively short distances (of about 40 km) in central East Antarctica. The reasons for the inhomogeneity may have been related to local topography and snow redistribution by wind in areas with extremely low accumulation, as well as to peculiarities of atmospheric circulation processes. According to the principal component analysis (PCA) and 5-day backward trajectories, it was determined that for site PV-10 (400 km from the Indian Ocean coast), zonal circulation in the lower troposphere associated with the cyclonic centers of the Southern Ocean was a leading process while the inland sites (VK-55 and SW-42) were influenced by a combination of processes involving meridional circulation, air mass transport, and transformation in the troposphere over the Antarctic continent.
... In addition, it has been long established that the relationship between isotopes and surface temperature may differ spatially and temporally (e.g., Jouzel et al., 1997) as a result of changes in the origin of moisture, atmospheric transport pathways (e.g., Schlosser et al., 2004), or precipitation seasonality (e.g., Sime et al., 2008;Masson- Delmotte et al., 2008;Sodemann and Stohl, 2009). Finally, non-climatic noise related to postdepositional effects associated, for instance, with wind scouring and water vapor also adds to the challenge of interpreting the ice-core signals (e.g., Ekaykin et al., 2014;Ritter et al., 2016;Casado et al., 2016). ...
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The Antarctic temperature changes over the past millennia remain more uncertain than in many other continental regions. This has several origins: (1) the number of high-resolution ice cores is small, in particular on the East Antarctic plateau and in some coastal areas in East Antarctica; (2) the short and spatially sparse instrumental records limit the calibration period for reconstructions and the assessment of the methodologies; (3) the link between isotope records from ice cores and local climate is usually complex and dependent on the spatial scales and timescales investigated. Here, we use climate model results, pseudoproxy experiments and data assimilation experiments to assess the potential for reconstructing the Antarctic temperature over the last 2 millennia based on a new database of stable oxygen isotopes in ice cores compiled in the framework of Antarctica2k (Stenni et al., 2017). The well-known covariance between δ¹⁸O and temperature is reproduced in the two isotope-enabled models used (ECHAM5/MPI-OM and ECHAM5-wiso), but is generally weak over the different Antarctic regions, limiting the skill of the reconstructions. Furthermore, the strength of the link displays large variations over the past millennium, further affecting the potential skill of temperature reconstructions based on statistical methods which rely on the assumption that the last decades are a good estimate for longer temperature reconstructions. Using a data assimilation technique allows, in theory, for changes in the δ¹⁸O–temperature link through time and space to be taken into account. Pseudoproxy experiments confirm the benefits of using data assimilation methods instead of statistical methods that provide reconstructions with unrealistic variances in some Antarctic subregions. They also confirm that the relatively weak link between both variables leads to a limited potential for reconstructing temperature based on δ¹⁸O. However, the reconstruction skill is higher and more uniform among reconstruction methods when the reconstruction target is the Antarctic as a whole rather than smaller Antarctic subregions. This consistency between the methods at the large scale is also observed when reconstructing temperature based on the real δ¹⁸O regional composites of Stenni et al. (2017). In this case, temperature reconstructions based on data assimilation confirm the long-term cooling over Antarctica during the last millennium, and the later onset of anthropogenic warming compared with the simulations without data assimilation, which is especially visible in West Antarctica. Data assimilation also allows for models and direct observations to be reconciled by reproducing the east–west contrast in the recent temperature trends. This recent warming pattern is likely mostly driven by internal variability given the large spread of individual Paleoclimate Modelling Intercomparison Project (PMIP)/Coupled Model Intercomparison Project (CMIP) model realizations in simulating it. As in the pseudoproxy framework, the reconstruction methods perform differently at the subregional scale, especially in terms of the variance of the time series produced. While the potential benefits of using a data assimilation method instead of a statistical method have been highlighted in a pseudoproxy framework, the instrumental series are too short to confirm this in a realistic setup.
... However, it is questioned whether the assumption holds in general that pre-depositional fractionation processes alone are the main influence on the isotopic composition of firn and ice, while seemingly fulfilled for large spatial and temporal scales. Particularly in low-accumulation areas for which the snow surface is exposed to the atmosphere for a substantial time, a variety of processes are thought to considerably modify the original atmospheric isotope signal during or after deposition of the snow, thus from seasonal to interannual timescales (e.g., Ekaykin et al., 2014, Hoshina et al., 2014Touzeau et al., 2016;Casado et al., 2016). ...
Thesis
Earth's climate varies continuously across space and time, but humankind has witnessed only a small snapshot of its entire history, and instrumentally documented it for a mere 200 years. Our knowledge of past climate changes is therefore almost exclusively based on indirect proxy data, i.e. on indicators which are sensitive to changes in climatic variables and stored in environmental archives. Extracting the data from these archives allows retrieval of the information from earlier times. Obtaining accurate proxy information is a key means to test model predictions of the past climate, and only after such validation can the models be used to reliably forecast future changes in our warming world. The polar ice sheets of Greenland and Antarctica are one major climate archive, which record information about local air temperatures by means of the isotopic composition of the water molecules embedded in the ice. However, this temperature proxy is, as any indirect climate data, not a perfect recorder of past climatic variations. Apart from local air temperatures, a multitude of other processes affect the mean and variability of the isotopic data, which hinders their direct interpretation in terms of climate variations. This applies especially to regions with little annual accumulation of snow, such as the Antarctic Plateau. While these areas in principle allow for the extraction of isotope records reaching far back in time, a strong corruption of the temperature signal originally encoded in the isotopic data of the snow is expected. This dissertation uses observational isotope data from Antarctica, focussing especially on the East Antarctic low-accumulation area around the Kohnen Station ice-core drilling site, together with statistical and physical methods, to improve our understanding of the spatial and temporal isotope variability across different scales, and thus to enhance the applicability of the proxy for estimating past temperature variability. The presented results lead to a quantitative explanation of the local-scale (1–500 m) spatial variability in the form of a statistical noise model, and reveal the main source of the temporal variability to be the mixture of a climatic seasonal cycle in temperature and the effect of diffusional smoothing acting on temporally uncorrelated noise. These findings put significant limits on the representativity of single isotope records in terms of local air temperature, and impact the interpretation of apparent cyclicalities in the records. Furthermore, to extend the analyses to larger scales, the timescale-dependency of observed Holocene isotope variability is studied. This offers a deeper understanding of the nature of the variations, and is crucial for unravelling the embedded true temperature variability over a wide range of timescales.
... Finally, non-climatic noise related to postdepositional effects associated for instance with wind scouring and water vapour make the interpretation of ice core signals further challenging (e.g. Ekaykin et al., 2014;Ritter et al., 2016;Casado et al., 2016). ...
Article
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The Antarctic temperature changes over the past millennia remain more uncertain than in many other continental regions. This has several origins: 1) the number of high resolution ice cores is small, in particular on the Antarctic Plateau and in some coastal areas in East Antarctica; 2) the short instrumental records limit the calibration period for reconstructions and the assessment of the methodologies; 3) the link between isotope records from ice cores and local climate is usually complex and dependent on the spatial and time scales investigated. Here, we use climate model results, pseudoproxy and data assimilation experiments to assess the potential of reconstructing the Antarctic temperature over the last two millennia based on a new database of stable oxygen isotopes in ice cores compiled in the framework of Antarctica2k (Stenni et al., 2017). The well-known covariance between δ¹⁸O and temperature is reproduced in the two isotope-enabled models used (ECHAM5/MPI-OM and ECHAM5-wiso), but is generally weak over the different Antarctic regions, limiting the skill of the reconstructions. Furthermore, the strength of the link displays large variations over the past millennium, further affecting the potential skill of temperature reconstructions based on statistical methods which rely on the assumption that the last decades are a good estimate for longer temperature reconstructions. Using a data assimilation technique allows in theory taking into account changes in the δ¹⁸O-temperature link through time and space. Pseudoproxy experiments confirm the benefits of using data assimilation methods instead of statistical ones that provide reconstructions with unrealistic variances in some Antarctic subregions. They also confirm that the relatively weak link between both variables leads to a limited potential for reconstructing temperature based on δ¹⁸O. The reconstruction skill is however higher and more uniform among reconstruction methods when the reconstruction target is the Antarctic as a whole rather than smaller Antarctic subregions. This consistency between the methods at the large scale is also observed when reconstructing temperature based on the real δ¹⁸O regional composites of Stenni et al. (2017). In this case, temperature reconstructions based on data assimilation confirm the long term cooling over Antarctica during the last millennium, and the later onset of anthropogenic warming compared to the simulations without data assimilation, especially visible in West Antarctica. Data assimilation also allows reconciling models and direct observations by reconstructing the East-West contrast regarding the recent temperature trends, indicating that internal variability likely plays a major role in driving this heterogeneous recent warming. This is further supported by the large spread of individual PMIP/CMIP model realizations regarding the recent warming pattern. As in the pseudoproxy framework, the reconstruction methods perform differently at the subregional scale, especially in terms of the variance of the produced time series. While the potential benefits of using a data assimilation method instead of a statistical one have been highlighted in a pseudoproxy framework, the instrumental series are too short to confirm it in a realistic setup.
... Nevertheless, isotopic analyses of both the precipitation and surface snow data from the East Antarctic Plateau revealed a clear seasonal cycle (Fujita and Abe, 2006;Landais et al., 2012;Stenni et al., 2016;Touzeau et al., 2016). Thus an important open question that needs to be addressed is whether this seasonal cycle is indeed archived in buried snow and whether stacking an array of snow pits sufficiently increases the signal-to-noise ratio to finally resolve those intra-annual timescales (Ekaykin et al., 2014;Altnau et al., 2015;Münch et al., , 2017. ...
Article
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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.
... This signal has then been subtracted from the measured signal over the period 1970-present. To remove the local noise component from the global signal, we followed previous studies of water isotopes in East Antarctica that stacked different records from several neighbor snow pits (Ekaykin et al., 2014;Münch et al., 2016). We thus put our three pits on their reconstructed chronology, described in the previous section, together to build a stack by averaging all the data in a temporal sliding window (Figure 3). ...
Article
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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 anti‐correlation 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 anti correlation and allow further investigation on the associated mechanism. At the interannual scale, the modelled 3H variability matches well with the SAM (Southern Annular Mode) index. At the seasonal scale, we show that modelled stratospheric tritium inputs in the troposphere are favored in winter cold and dry conditions.
... This hypothesis receives support from the observation that the TO C350V cycles identified here are similar in period and relative amplitude to comparable cycles of the AAO that have been identified independently from more contemporary tree-ring data [26,27] and from stacked temperature-proxy records from Vostok snow pits [32]. Similarly, westerly wind records in the SH (Falkland Islands) for the past 2600 years as assessed from records of pollen distribution show discernible AAO spectral peaks at 242, 185, 150 and 95 years that average 168 years [72] (Figure 5a, p. 194), similar to the 193-year discernible peak in the Holocene spectral periodogram of the ACO (Figure 3) and the 162-year average period over the last 2,600 years (Figure 1d). ...
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We report a previously-unexplored natural temperature cycle recorded in ice cores from Antarctica—the Antarctic Centennial Oscillation (ACO)—that has oscillated for at least the last 226 millennia. Here we document the properties of the ACO and provide an initial assessment of its role in global climate. We analyzed open-source databases of stable isotopes of oxygen and hydrogen as proxies for paleo-temperatures. We find that centennial-scale spectral peaks from temperature-proxy records at Vostok over the last 10,000 years occur at the same frequencies (±2.4%) in three other paleoclimate records from drill sites distributed widely across the East Antarctic Plateau (EAP), and >98% of individual ACOs evaluated at Vostok match 1:1 with homologous cycles at the other three EAP drill sites and conversely. Identified ACOs summate with millennial periodicity to form the Antarctic Isotope Maxima (AIMs) known to precede Dansgaard-Oeschger (D-O) oscillations recorded in Greenland ice cores. Homologous ACOs recorded at the four EAP drill sites during the last glacial maximum appeared first at lower elevations nearest the ocean and centuries later on the high EAP, with latencies that exceed dating uncertainty >30-fold. ACO homologs at different drill sites became synchronous, however, during the warmer Holocene. Comparative spectral analysis suggests that the millennial-scale AIM cycle declined in period from 1500 to 800 years over the last 70 millennia. Similarly, over the last 226 millennia ACO repetition period (mean 352 years) declined by half while amplitude (mean 0.67 °C) approximately doubled. The period and amplitude of ACOs oscillate in phase with glacial cycles and related surface insolation associated with planetary orbital forces. We conclude that the ACO: encompasses at least the EAP; is the proximate source of D-O oscillations in the Northern Hemisphere; therefore affects global temperature; propagates with increased velocity as temperature increases; doubled in intensity over geologic time; is modulated by global temperature variations associated with planetary orbital cycles; and is the probable paleoclimate precursor of the contemporary Antarctic Oscillation (AAO). Properties of the ACO/AAO are capable of explaining the current global warming signal.
... Still, on the East Antarctic Plateau, a clear seasonal cycle is depicted in the isotopic composition of the precipitation (Fujita and Abe, 2006;Landais et al., 2012;Stenni et al., 2016) and of the surface snow (Touzeau et al., 2016). So far, whether this seasonal cycle is archived or not in buried snow, and thus, whether stacking an array of snow pits enables us to increase the signal to 20 noise ratio and depict a climatic record at the seasonal scale from water isotopic signal is an important open question (Ekaykin et al., 2014;Altnau et al., 2015;Münch et al., 2016Münch et al., , 2017. ...
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The oldest ice core records are obtained from the East Antarctic plateau. Water isotopes records are key to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all the processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in Rayleigh distillation and isotope enabled climate models. However, a quantitative understanding of processes potentially altering the snow isotopic composition after the deposition is still missing. In low accumulation sites, such as those found in Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretation of isotopic composition. Here, we combine observations of isotopic composition in the vapour, the precipitation, the surface snow and the buried snow from Dome C, a deep ice core site on the East Antarctic Plateau. At the seasonal scale, we suggest a significant impact of metamorphism on surface snow isotopic signal compared to the initial precipitation signal. Particularly, in summer, exchanges of water molecules between vapour and snow are driven by the sublimation/condensation cycles at the diurnal scale. Using highly resolved isotopic composition profiles from pits in five Antarctic sites, we identify common patterns, despite different accumulation rates, which cannot be attributed to the seasonal variability of precipitation. Altogether, the difference in the signals observed in the precipitation, surface snow and buried snow isotopic composition constitute evidences of post-deposition processes affecting ice core records in low accumulation areas.
... Following Ekaykin et al. (2014), who reported a closer relationship between Vostok isotopic data and summer temperature than with the annual mean temperature, we performed additional analyses of relationships between our stacked isotope record and other temperature time series (e.g. monthly or seasonal temperature anomalies), but this does not improve the isotope-temperature correlation. ...
Article
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We use isotopic composition (d�D) data from six sites in Princess Elizabeth Land (PEL) in order to reconstruct air temperature variability in this sector of East Antarctica over the last 350 years. First, we use the present-day instrumental mean annual surface air temperature data to demonstrate that the studied region (between Russia’s Progress, Vostok and Mirny research stations) is characterized by uniform temperature variability. We thus construct a stacked record of the temperature anomaly for the whole sector for the period of 1958–2015. A comparison of this series with the Southern Hemisphere climatic indices shows that the short-term inter-annual temperature variability is primarily governed by the Antarctic Oscillation (AAO) and Interdecadal Pacific Oscillation (IPO) modes of atmospheric variability. However, the low-frequency temperature variability (with period >27 years) is mainly related to the anomalies of the Indian Ocean Dipole (IOD) mode. We then construct a stacked record of d�D for the PEL for the period of 1654–2009 from individual normalized and filtered isotopic records obtained at six different sites (“PEL2016” stacked record). We use a linear regression of this record and the stacked PEL temperature record (with an apparent slope of 9�5.4‰�/C) to convert PEL2016 into a temperature scale. Analysis of PEL2016 shows a 1�0.6 �C warming in this region over the last 3 centuries, with a particularly cold period from the mid-18th to the mid-19th century. A peak of cooling occurred in the 1840s – a feature previously observed in other Antarctic records. We reveal that PEL2016 correlates with a low-frequency component of IOD and suggest that the IOD mode influences the Antarctic climate by modulating the activity of cyclones that bring heat and moisture to Antarctica. We also compare PEL2016 with other Antarctic stacked isotopic records. This work is a contribution to the PAGES (Past Global Changes) and IPICS (International Partnerships in Ice Core Sciences) Antarctica 2k projects.
... Still, on the East Antarctic Plateau, a significant seasonal cycle is depicted in the isotopic composition of the precipitation (Fujita and Abe, 2006;Landais et al., 2012;Stenni et al., 2016) and of the surface snow (Touzeau et al., 2016). So far, whether this seasonal cycle is archived or not in buried snow, and thus, whether stacking an array of snow pits permits to increase the signal to noise ratio and depict a climatic record at the seasonal scale from water isotopic signal remain unclear (Ekaykin et al., 2014;Altnau et al., 2015;Münch et al., 2016). 20 Several studies have focused on understanding how is the climatic signal archived in the isotopic composition of snow and ice on the East Antarctic Plateau. ...
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The oldest ice core records are obtained from the East Antarctic plateau. Water stable isotopes records are key for reconstructions of past climatic conditions both over the ice sheet and at the evaporation source. The accuracy of such climate reconstructions crucially depends on the knowledge of all the processes affecting the water vapour, precipitation and snow isotopic composition. Atmospheric fractionation processes are well understood and can be integrated in Rayleigh distillation and complex isotope enabled climate models. However, a comprehensive quantitative understanding of processes potentially altering the snow isotopic composition after the deposition is still missing, especially for exchanges between vapour and snow. In low accumulation sites such as found on the East Antarctic Plateau, these poorly constrained processes are especially likely to play a significant role. This limits the interpretation of isotopic composition from ice core records, specifically at short time scales. Here, we combine observations of isotopic composition in the vapour, the precipitation, the surface snow and the buried snow from various sites of the East Antarctic Plateau. At the seasonal scale, we highlight a significant impact of metamorphism on surface snow isotopic signal compared to the initial precipitation isotopic signal. In particular, in summer, exchanges of water molecules between vapour and snow are driven by the sublimation/condensation cycles at the diurnal scale. Using highly resolved isotopic composition profiles from pits in five East Antarctic sites, we identify a common 20 cm cycle which cannot be attributed to the seasonal variability of precipitation. Altogether, the smaller range of isotopic compositions observed in the buried and in the surface snow compared to the precipitation, and also the reduced slope between surface snow isotopic composition and temperature compared to precipitation, constitute evidences of post-deposition processes affecting the variability of the isotopic composition in the snow pack. To reproduce these processes in snow-models is crucial to understand the link between snow isotopic composition and climatic conditions and to improve the interpretation of isotopic composition as a paleoclimate proxy.
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Central Antarctica is characterized by a crucial lack of information on climate variability during the late Holocene. The study of firn cores obtained from the central part of the East Antarctic Ice Sheet is essential for the reconstruction of the paleoclimatic conditions at the continental and regional scales over the past 2,000 years (the Late Holocene). Based on glaciological and isotopic data from the shallow VK16 core drilled in the vicinity of Vostok Station over the periods of the 62th (2016–2017) and 63th (2017–2018) summer seasons of RAE, climatic characteristics have been reconstructed for the period 216 BC – 2010 AD. Studies of the VK16 core were carried out in two stages: firn density and electrical conductivity measurement (ECM), as well as sampling, was performed in the glaciological laboratory of the 5G drilling complex (Vostok Station) soon after the firn recovery, while the isotopic composition of the core samples was measured by a Picarro L-2120i laser analyzer in the Climate and Environmental Research Laboratory of AARI. In the ECM profile of the core, we discovered 14 absolute age markers (layers containing the products of known volcanic eruptions). These markers have allowed us to develop a robust chronostratigraphic scale for this core. We have shown that the main feature of the Late Holocene climate in this part of Antarctica is that the near-surface air temperature remained essentially constant throughout the whole time period under consideration. At the same time, the snow accumulation rate varied significantly around a mean value of 1.83 g cm–2 year–1, while the last 200 years were characterized by the highest snow accumulation rate, equal to 2.08 g cm–2 year–1. In this paper, we describe methods for studying firn cores, which can be useful for further research, and present first preliminary data on the climate variability in the vicinity of Vostok Station during the late Holocene.
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The Medieval Climate Anomaly (MCA) is a well-recognized climate perturbation in many parts of the world, with a core period of 1000–1200 CE. Here we are mapping the MCA across the Antarctic region based on the analysis of published palaeotemperature proxy data from 60 sites. In addition to the conventionally used ice core data, we are integrating temperature proxy records from marine and terrestrial sediment cores as well as radiocarbon ages of glacier moraines and elephant seal colonies. A generally warm MCA compared to the subsequent Little Ice Age (LIA) was found for the Subantarctic Islands south of the Antarctic Convergence, the Antarctic Peninsula, Victoria Land and central West Antarctica. A somewhat less clear MCA warm signal was detected for the majority of East Antarctica. MCA cooling occurred in the Ross Ice Shelf region, and probably in the Weddell Sea and on Filchner-Ronne Ice Shelf. Spatial distribution of MCA cooling and warming follows modern dipole patterns, as reflected by areas of opposing temperature trends. Main drivers of the multi-centennial scale climate variability appear to be the Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO) which are linked to solar activity changes by nonlinear dynamics.
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Here we present Antarctic snow accumulation variability at the regional scale over the past 1000 years. A total of 79 ice core snow accumulation records were gathered and assigned to seven geographical regions, separating the high-accumulation coastal zones below 2000 m of elevation from the dry central Antarctic Plateau. The regional composites of annual snow accumulation were evaluated against modelled surface mass balance (SMB) from RACMO2.3p2 and precipitation from ERA-Interim reanalysis. With the exception of the Weddell Sea coast, the low-elevation composites capture the regional precipitation and SMB variability as defined by the models. The central Antarctic sites lack coherency and either do not represent regional precipitation or indicate the model inability to capture relevant precipitation processes in the cold, dry central plateau. Our results show that SMB for the total Antarctic Ice Sheet (including ice shelves) has increased at a rate of 7 ± 0.13 Gt decade⁻¹ since 1800 AD, representing a net reduction in sea level of ∼ 0.02 mm decade⁻¹ since 1800 and ∼ 0.04 mm decade⁻¹ since 1900 AD. The largest contribution is from the Antarctic Peninsula (∼ 75 %) where the annual average SMB during the most recent decade (2001–2010) is 123 ± 44 Gt yr⁻¹ higher than the annual average during the first decade of the 19th century. Only four ice core records cover the full 1000 years, and they suggest a decrease in snow accumulation during this period. However, our study emphasizes the importance of low-elevation coastal zones, which have been under-represented in previous investigations of temporal snow accumulation.
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The results of Russian climate studies (published in 2011–2014) based on the review prepared for the National Report on Meteorology and Atmospheric Sciences submitted to the 26th General Assembly of the International Union of Geodesy and Geophysics (Prague, June 22–July 2, 2015)¹ are presented.
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The isotopic composition of water in ice sheets is extensively used to infer past climate changes. In low-accumulation regions their interpretation is, however, challenged by poorly constrained effects that may influence the initial isotope signal during and after deposition of the snow. This is reflected in snow-pit isotope data from Kohnen Station, Antarctica, which exhibit a seasonal cycle but also strong interannual variations that contradict local temperature observations. These inconsistencies persist even after averaging many profiles and are thus not explained by local stratigraphic noise. Previous studies have suggested that post-depositional processes may significantly influence the isotopic composition of East Antarctic firn. Here, we investigate the importance of post-depositional processes within the open-porous firn (≳ 10 cm depth) at Kohnen Station by separating spatial from temporal variability. To this end, we analyse 22 isotope profiles obtained from two snow trenches and examine the temporal isotope modifications by comparing the new data with published trench data extracted 2 years earlier. The initial isotope profiles undergo changes over time due to downward advection, firn diffusion and densification in magnitudes consistent with independent estimates. Beyond that, we find further modifications of the original isotope record to be unlikely or small in magnitude (≪ 1 ‰ RMSD). These results show that the discrepancy between local temperatures and isotopes most likely originates from spatially coherent processes prior to or during deposition, such as precipitation intermittency or systematic isotope modifications acting on drifting or loose surface snow.
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Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850–2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.
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Spatial and temporal variability of a sea-salt aerosol (Na⁺) concentration was investigated in snow-firn cores and snow pits taken at four sites of the Indian Ocean sector of the East Antarctica (along a profile between stations Progress and Vostok: PV-10, NVFL-1, SW-42, and the Vostok point). In long annually resolved Na⁺ records, we had revealed the following periodicities: 17 to 95-year (Vostok) and 29 to 52-year (NVFL-1), while the shorter records are characterized by 8-year periodicity. The Na⁺ concentrations decrease as the snow accumulation increases (especially, at the Vostok station), and this is evidence for a presence of «dilution effect» in the sites with the great part of «dry precipitation». The closest relationship was revealed between changes in flows of Na⁺ at points SW-42, and PV-10. Variability of the Na⁺ fluxes had been linked to the circulation indices (AAO, PDO, SOI, MEI, SPO) and the sea level pressure in the Southern Hemisphere, as well as to occurrence of Elementary Circulation Mechanisms (ECM). The revealed irregularity of the Na⁺ precipitation over the area under investigation is caused by different atmospheric circulation patterns as well as by influence of basic Action Centers of the Atmosphere (ACA) in the Southern Hemisphere. The closest relationship is found to take place with South Pacific ACA (Vostok, 1976-2009) and with the South Indian ACA (SW-42 and PV-10). A presence of distant atmospheric relations (including one with El Nino) had been revealed for the inland areas. Changes in features of the atmospheric circulation in the South Indian Ocean over the last 200-year period have been reconstructed on the basis of summarized Na⁺ records from the Vostok station area. Distinctive feature of the atmospheric circulation is the 40-year periodicity with its increasing intensity during the following periods: 1805-1820, 1830-1860, 1890-1900, 1940-1950, and 1980-2000. In addition, we had revealed that changes in the atmospheric circulation in the Indian Ocean (Southern Hemisphere) were synchronous with similar variability of the circulation in the Siberian (Northern Hemisphere) sector.
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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.
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