Variations of snow accumulation rate in Central Antarctica over the last 250 years

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

Fifty years of instrumental surface mass balance observations at Vostok Station, central Antarctica

We present the surface mass balance (SMB) dataset from Vostok Station's accumulation stake farms which provide the longest instrumental record of its kind obtained with a uniform technique in central Antarctica over the last 53 years. The snow build-up values at individual stakes demonstrate a strong random scatter related to the interaction of wind-driven snow with snow micro-relief. Because of this depositional noise, the signal-to-noise ratio (SNR) in individual SMB time series derived at single points (from stakes, snow pits or firn cores) is as low as 0.045. Averaging the data over the whole stake farm increases the SNR to 2.3 and thus allows us to investigate reliably the climatic variability of the SMB. Since 1970, the average snow accumulation rate at Vostok has been 22.5 ± 1.3 kg m−2 yr−1. Our data suggest an overall increase of the SMB during the observation period accompanied by a significant decadal variability. The main driver of this variability is local air temperature with an SMB temperature sensitivity of 2.4 ± 0.2 kg m−2 yr−1 K−1 (11 ± 2% K−1). A covariation between the Vostok SMB and the Southern Oscillation Index is also observed

Изменение температуры в Центральной Антарктиде после крупных вулканических извержений во втором тысячелетии нашей эры

Volcanic forcing is one of the major drivers of climatic variability on Earth during the last millennium before the beginning of the industrial era, combined with solar activity, Milanković orbital forcing and greenhouse gas concentration. Large volcanic eruptions (with Volcanic Explosivity Index of 6 or more) eject a huge amount of sulfur dioxide into stratosphere thus reducing the amount of incoming solar radiation. The corresponding cooling may exceed 1 °C and lasts about 5 years. The identification of the volcanic events is carried out with the use of firn and ice core data drilled in the polar ice sheets, while the climatic response to the eruptions is studied with the use of dendrochronology and other terrestrial data, mainly in the Northern Hemisphere. Thus, the reaction of the Southern Hemisphere’s climate to the volcanic forcing is understood to a lesser extent. Here we use stable water isotope data (δ18O and dxs parameter, dxs = δD – 8 · δ18O) from 4 firn cores in order to study the temperature change in central Antarctica (in the vicinity of Vostok Station) after 5 major eruptions of the 2nd millennium of the Common Era: Samalas (1257), Unknown Event 1459 CE, Huaynaputina (1600), Parker (1641) and Tambora (1815). The isotopic composition of the cores was measured in the Climate and Environmental Research Laboratory of the Arctic and Antarctic Research Institute (St. Petersburg) with the use of Picarro L2130-i and L2140-i laser analyzers. We show that a post-eruption cooling in central East Antarctica is about 0.52 °C and lasts for about 5 years. At the same time, the temperature in the moisture source decreases to a lesser extent (0.46 °C), but the cooling lasts longer. We need to emphasize that only through using 4 parallel cores was it possible to significantly reduce the amount of the “deposition noise” in the isotopic records and detect the post-volcanic cooling in central East Antarctica.Вулканическая активность является одним из важнейших факторов естественной климатической изменчивости позднего голоцена до начала индустриальной эпохи. Влияние вулканов на климат изучается в основном по дендрохронологическим записям Северного полушария, тогда как о влиянии крупных извержений на температуру воздуха в полярных широтах Южного полушария известно существенно меньше. В настоящей работе использованы данные по изотопному составу (δ18O и δD) из 4 фирновых кернов для изучения изменения температуры в Центральной Антарктиде (окрестностях станции Восток) после 5 крупных извержений второго тысячелетия нашей эры: Самалас (1257 г.), Неизвестное Событие (1459 г.), Уайнапутина (1600 г.), Паркер (1641 г.) и Тамбора (1815 г.). Показано, что похолодание после извержения составляет около 0,52 °C и длится около 5 лет, при этом температура в источнике влаги снижается в меньшей степени (0,46 °С), но холодный период длится дольше

A record of volcanic eruptions over the past 2,200 years from Vostok firn cores, central East Antarctica

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

В ПОИСКАХ ДРЕВНЕЙШЕГО ЛЬДА АНТАРКТИДЫ

One of the key priority tasks for the international Antarctic community is drilling and studying old Antarctic ice with age exceeding 1  million years in order to investigate possible reasons for the Mid-Pleistocene Transition. During the 2017–2018 austral season at Vostok Station, we carried out microscopic study of geometrical properties of the crystalline inclusions of air hydrates in ice core samples from boreholes 5G‑3 (Vostok) and DC2 (EPICA DC) in depth intervals where the age of the ice exceeded 400,000 years. The obtained data confirmed the existence of a robust linear relationship between the mean radius of the hydrates and the age of the ice in the bottom part of the East Antarctic ice sheet, and will be useful for further development of the new dating technique based on the phenomena of hydrate growth in polar ice. Preliminary, the age of the atmospheric ice bedded at Vostok at a depth of3538 m, inferred from the data on the size of the hydrates, amounts to 1.3±0.17 million years. The existence of ice older than 1 million years in the vicinity of Vostok implies that in the area of Ridge B, where the ice flow line which passes through Vostok Station originates, even older ice, with undisturbed stratigraphy, may exist. It would be desirable therefore to carry out a glacio-geophysical traverse to Ridge B in order to implement a detailed study of Dome B area aimed at identifying the most suitable site for a new deep drilling of the Antarctic ice sheet.Сделан краткий обзор деятельности международного антарктического сообщества по поиску древнего льда в Антарктиде. Приведены предварительные результаты работ, полученные на станции Восток в период 63-й Российской антарктической экспедиции, которые подтверждают, что возраст льда в уже полученном на станции керне превышает 1 млн лет. Сформулированы первоочередные задачи дальнейших исследований древнего антарктического льда на станции Восток и в районе Ледораздела В

Climatic variability in the era of MIS-11 (370-440 ka BP) according to isotope composition (delta D, delta O-18, delta O-17) of ice from the Vostok station cores

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

Archival processes of the water stable isotope signal in East Antarctic ice cores

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

Сохранность климатического сигнала в слоях древнего льда в районе Купола В (Антарктида)

In this work we have presented the results of numerical modeling of the age and temperature distribution in ice layers at Dome B site (79,02° S, 93,69° E, altitude 3807 m a.s.l., ice thickness about 2.5 km), located 300 km to the west from Russian Antarctic station Vostok. Dome B is situated on the onset of the ice flow line passing through deep borehole 5G, and is considered as one of the most promising places to search for and to study the Easth’s oldest ice with the age of up to 1.5 Ma. According to our calculations, all realistic scenarios show the ice age at 60 m above the ice base to be considerably older than 1 Ma, and the glacier base temperature is well below the pressure melting point (−1.8 °С for pressure = 23 MPa). For the most likely scenario (accumulation rate 1.8 g/(cm2 year), effective ice surface temperature −64 °С and geothermal heat flux 60 mW/m2) the ice age is 1.4 Ma and the basal temperature is about −13 °С that is close to the earlier predictions from a 2D‑model. Maximum estimate of the «diffusion length» in the old ice (for the scenario in which the basal temperature reaches the melting point, and in which 30% of «excess diffusion» is taken into account) is 5.2 cm. In 1.4 Ma-old ice a 40-ka climatic cycle is squeezed into a 290-cm thick ice layer. For this ratio of wave length and diffusion length the climatic signal attenuation (ratio between the signal amplitude after and before the diffusive smoothing) is 0.6%. Thus, due to the relatively low ice temperature here we may expect a nearly undisturbed climatic curve in the old ice core that will be drilled one day at Dome B. At the same time shorter oscillations with the wavelengths of < 1500 years will be totally erased by diffusion.Представлены результаты моделирования возраста и температуры льда для Купола В (79,02° ю.ш., 93,69° в.д., высота 3807 м над ур. моря, толщина льда около 2,5 км) в Антарктиде. Для всех сценариев возраст льда на отметке 60 м выше ложа ледника составляет более 1 млн лет, а для наиболее вероятного сценария – 1,4 млн лет. Температура ложа для всего диапазона реалистичных оценок геотермального потока тепла находится ниже точки плавления и для наиболее вероятного сценария равна около −13 °С. Расчётное ослабление амплитуды 40‑тысячелетнего климатического цикла в древнем льду за счёт молекулярной диффузии составляет около 0,6%. Результаты исследования позволяют сделать вывод, что Купол В – перспективное место для извлечения нового глубокого керна, с помощью которого можно будет получить ненарушенный климатический сигнал за последние 1,4 млн лет