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Project titleClimate and environmental reconstructions over the last millennium from Mt. Elbrus ice cores in the Northern Caucasus and southern part of European Russia

KeywordsIce cores, climatic changes, high resolution reconstructions, glacier variations, climate models, Elbrus, radio-echo sounding

Annotation
The question of the presence of ancient ice in the Caucasus is still open. According to the calculations of the mass turnover time of Caucasian glaciers based on the accumulation rate, ice thickness and temperature, it was estimated as several hundred years. Direct dating of bottom layers in the ice core from the Western plateau of Elbrus showed that the ice age can reach 2000 years. Other potential places where ancient ice may be encountered are the upper part of the Bezengi wall and the Eastern peak of Elbrus. Our 2017 studies showed that the accumulation at the Eastern crater is about 500 mm w.e., i.e. 3 times less than on the Western plateau, and the temperature of the snow-firn reaches -19 °C. This suggests that relatively ancient ice may be present in the bottom of the glacier. At the same time, in the analysis of a shallow firn core, pronounced seasonal variations in the oxygen isotopic composition (δ18O) were found that persist in the thickness despite the deflation of a part of the annual layer in the winter. We suggest that the ice in the crater of the Eastern peak of Elbrus may be more ancient in comparison with other glaciers of the Caucasus. Therefore, this glacier will be the main object of research for the next two years. A fundamentally new task to be solved in the frame of the project will be to establish a relationship between the isotopic composition of oxygen and hydrogen in the precipitation depositing on the Azau meadow with the distribution of δ18O and δ2H in seasonal snow pits on the slopes of the Mt. Elbrus on different altitudes. As for the Western plateau of the Mt. Elbrus, we identified a great variability of the snow accumulation rate. It is associated with a strong wind drift, as well as a frequent change in the air masses bringing moisture to the area. We are supposed to trace changes of the general pattern in seasonal isotopic records formation at the foot and on the slopes (peaks) of the Mt. Elbrus. All the precipitation events will be linked to the moisture origin area and its trajectory toward Mt. Elbrus using the HYSPLIT NOAA model and the baric field maps. A foreseen perspective of this project could be fine and non-trivial study of the stable water isotopic composition link to the precipitations of different origin: convective, front and orographic. It will give us a possibility to trace the predominant precipitation type differentiated by seasons and to establish influence of seasonality in precipitation types to the isotopic signal in the ice core samples. In order to interpret the climatic signal in the ice core isotopic record we will imply the potential energy of convection, which was successfully used in the precipitation reconstruction. The implication of this parameter will allow distinguishing more clearly between the precipitation of cold and warm seasons and using the meteorological observations on the nearest stations, such as surface air temperature and precipitation amount, more trustfully. We will perform a spore-pollen analysis and determination of non-pollen palynomorphs of a 24-meter firn core to separate annual horizons in cores for summer and winter seasons and compare with the current plant dusting regime in the region. Trace elements analysis of Elbrus ice cores will reveal short-term regional changes in the atmospheric composition over the past centuries. Special attention will be paid to the analysis of the influence of the volcanic activity of Elbrus on the chemical composition of ice cores obtained earlier, as well as new samples that are planned to be obtained in the region of the Eastern Peak. For a quantitative assessment of the effect of microparticle deposition on the melting of snow and ice, a detailed knowledge of the size distribution of dust particles, dust flux and concentrations is required. It is also necessary to better understand the spatial variability of dust flux on a regional and global scale. For the next two years, the project aims to analyze the content of microparticles in Elbrus ice cores, determine the particle size and mass, and also calculate the dust flux. In this project, methane content in ice cores will be analyzed. We will combine the new methane concentration data from the Elbrus ice cores with published records from low latitudes. New data on the quantitative contribution of methane sources will allow to verify methane flux models. The regional concentration of methane in the atmosphere during the Late Holocene will be reconstructed. By means of the wavelet transform of methane concentrations series, the presence of cyclic fluctuations (possibly decade or century) and their modification with time will be analyzed, and assumptions about the causes of the observed phenomenon will be advanced. Based on the Monin-Obukhov methods and eddy covariance, snow drift will be calculated. To achieve this goal, additional measurements of turbulent momentum, heat and moisture flows in the accumulation zone will be carried out. A simple algorithm for calculating the orographic precipitation additive and its verification according to ice core data will be created. The orographic component of the condensation rate will be calculated based on the saturation pressure of water vapor changes with altitude considering adiabatic air cooling. The contribution of the orographic factor to the process of condensation of water vapor and the potential water content of clouds will be estimated. The condensation rate will be calculated from air temperature, humidity and wind speed on isobaric surfaces ERA5 reanalysis data. The obtained values of the orographic additive will be compared with the nearest meteorological station data and ice cores. An analysis of the cyclone trajectories bringing precipitation to the Central Caucasus will be made on the base of ERA5 reanalysis data. “lifetime” of the atmospheric moisture will be calculated for the Elbrus and Central Caucasus area using mesoscale numerical atmospheric WRF-ARW model. In the proposed project, we will solve two problems that differ significantly in their statement: 1) creating a flow model for an ice-firn mass with its subsequent dating (for two Elbrus glaciers); 2) reconstruction of temperature changes on the surface of the glacier based on the results of borehole temperature measurements. The solution of the first problem will be based on the application of a three-dimensional Stokes flow model for a compressible viscous heat-conducting fluid (ice). In this case, the rheological law for porous ice will be used. The dating of the ice-firn thickness will be performed by solving the boundary value problem for the transport equation in the three-dimensional domain occupied by the glacier. The second task – reconstruction of past temperature changes - is an ill-posed inverse problem of mathematical physics. To carry out the reconstruction, it is proposed to use the Bayesian approach and Markov Chain Monte Carlo methods in conjunction with solving the direct problem of heat conduction. In both cases, the simulation will be performed numerically. Detailed GPR survey will be completed at the wester plateau using low frequency pulsed radar VIRL-7 to clarify the previous data on the ice thickness and bedrock topography. Detailed geodetic survey will be done by differential GPS -Topcon GB 500. In order to assess the accumulation of snow and its spatial distribution we will conduct a survey using high -frequency radar (400-800 MHz ). Analysis of internal reflections on the radiograms will evaluate the dielectric constant of each layer, the velocity of electromagnetic waves propagation in layers of snow and firn will enable the determination of its density.

Expected results
As a result of the project, an ice core in the crater of the Eastern Peak will be obtained and borehole temperature will be measured, detailed maps of the thickness of the ice and the relief of the subglacial bed will be completed. The implementation of the ice flow and dating model for the West Plateau of Elbrus will be completed and glacier on the West Plateau will be dated on the basis of a three-dimensional model. As a result of clarification of the air temperature/isotopic composition of precipitation relationship, air temperatures will be reconstructed using the isotopic composition (δ18O and δ2H) of Elbrus ice cores. As a result of the spore-pollen analysis of Elbrus cores, new data on the modern and multi-season regime of plant dusting will be obtained and the main pollen sources will be identified. For the first time, the methane content in the atmosphere of the Caucasus will be reconstructed using ice core data. To quantify the effect of microparticle deposition on the melting of snow and ice, an analysis of the microparticle content in Elbrus ice cores will be carried out, particle sizes and masses will be determined, and dust flux on glaciers will be calculated. Trace element composition analysis of Elbrus ice cores will reveal short-term regional changes in the composition of the atmosphere over the past centuries. Special attention will be paid to the analysis of the influence of the volcanic activity of Elbrus on the chemical composition of cores. These results are important not only from a scientific, but also from a practical point of view, as they will fill in the gaps in knowledge about climate change in high mountain regions, and enable the assessment of the regional characteristics of air pollution. The data on ice temperature distribution in the crater of the Eastern peak of Elbrus are important for determining heat flux and evaluating the volcanic activity.

Annotation of the results obtained in 2021
An ice core, 92.4 m, was recovered in the eastern part of the Katyn plateau in the accumulation area of Bezengi glacier at 4750. The goal of this study was to search the oldest ice in the Caucasus and compare new results with ice-cores records from Elbrus. Annual accumulation rate has been estimated on the base of the water stable isotopic composition measured in the snow pit samples. The measured temperature in the borehole varies from -10.3 ° C at the 10-meter depth to -14 ° C near bedrock. Daily snow drift and turbulent heat flux was estimated on the base of meteorological observation data at the drilling site. Spectral analysis has shown the important role of katabatic and foehn effects in heat transfer. A relationship between isotopic composition of precipitation and daily air temperature has been determined. A large variability of isotope-temperature record was established for the cold season compared to the warm period, that is associated with the predominance of advective and convective moisture transfer in different seasons. The analysis of the isotopic composition of the Elbrus ice-core data has been carried out. Post-depositional effect in the isotopic composition was estimated. It was found that diffusion is not capable of smoothing seasonal signal in the isotopic record. Mean annual air temperature was reconstructed on the base of Elbrus ice-core water isotopic records since 1821. Ice flow velocity and pressure fields were calculated for the Western Plateau and Eastern Elbrus Summit glaciers using a three-dimensional stationary full Stokes model with a rheological law for a compressible nonlinearly viscous medium. A statistical analysis of the ice layer thickness temporal variability was carried out for the Western Plateau of Elbrus. The relationship between the total annual thickness of ice layers and duration of calm solar periods is revealed. Numerical experiments for the physically substantiate the results were performed using the complete SNOWPACK snow cover model. The simulation results showed an increase in the number of ice layers in the glacier in the 21st century, which confirms the "radiation" nature of their formation. It is shown that snow accumulation Elbrus ice-core records describe the annual precipitation field within a radius of 10–50 km with maximum accuracy, and at a distance of 50–100 km - with acceptable accuracy. The orographic effect of precipitation increase was assessed for the western slope of Elbrus. An algorithm for that has been developed based on calculating the condensation rate from data on temperature, partial pressure of water vapor and wind speed at standard isobaric levels. The annual amount of sublimation can reach 50 mm, or 3-4% of the precipitation, in the Elbrus high-altitude areas. It is shown that incoming short-wave radiation over the Greater Caucasus could increase by 30 W / m2 for 2015–2020 in comparison with 1951-1980th. Anomalies of the incoming short-wave radiation are the most important factor in the rapid degradation of glaciers in the Greater Caucasus. Annual amount of precipitation was divided for winter and summer ones using seasonal variation of ammonium ions in the ice core. A calendar of warm and cold seasons has been compiled over the past 40 years based on the convective available potential energy obtained from ERA5 reanalysis. A relationship between reconstructed snow accumulation on the Elbrus Western Plateau and precipitation at the meteorological stations has been clarified using that calendar. It has been established that annual accumulation on the Western Plateau are related to precipitation. The contribution of other factors is insignificant. The relationship between the humid periods and glacier dynamic in the North Caucasus in the 19th – 20th centuries was revealed. A snow accumulation map has been compiled for the Eastern Summit of Elbrus based on the high-frequency radar survey data. For the first time, the methane concentration in the Elbrus ice core was measured with high resolution. The results were compared with discrete records from other regions and showed the presence of various multi-decadal trends reflecting regional features of methane variability in the atmosphere. An increase of methane concentration is estimated for industrial and post-industrial periods. Considerable taxonomic diversity of pollen and spores in the Elbrus ice core was found from palynological analysis. The samples contained 47 taxa of pollen and spores, 9 varieties of fungi, 1 genus of shell amoebae, feather barrels, spherical black carbon, and micron. The main factor determining the taxonomic composition and concentration of microparticles in the palynological spectra of the Elbrus glaciers is annual seasonality. The seasonal dynamics of fire regimes based on the concentration of coal microparticles in palynological spectra has been investigated. Their insignificant variability in the same seasons in different years testifies to the stability of fire conditions over research period. An assessment of the climatic and dynamic parameters of glaciation in the cold firn zone of Elbrus has been made. The estimate was based on firn density and temperature data from two ice cores at the East Summit (2020) and the Western Plateau (2009). The calculation results showed that the inclusion of the heat flux from the lower boundary significantly improves the calibration efficiency for all parameterizations of the used mathematical model. Man-made limestone dump and the tailing dump of the Tyrnauz Mining Company are the main source of trace elements for the Elbrus glaciers. It was shown that typical for volcanic aerosols trace elements are varied seasonally. Their contribution to trace element content is insignificant. The concentration of mineral dust in the Elbrus glaciers has been determined and its annual fluxes have been estimated. Dust deposition on the Caucasus glaciers from the Middle East and Sahara deserts are investigated. The contribution of desert dust is estimated as 40% of the total microparticle flux for the 2007-2009 period. Trends of the two major nitrogen-derived pollutants (ammonium and nitrate) in ice are considered with respect to anthropogenic emissions of ammonia (mainly from agricultural activity) and nitrogen oxides (fossil fuel combustion). Trend of organic carbon (OC) observed in the Elbrus ice over the 20th century is weaker than in the Alps (30% instead of more than 100%). The 14C data indicate that most of this increase is related to anthropogenic emissions, and that no significant increase of biogenic emissions is detected at this site.

Publications

1. I.I. Lavrentiev, S.S. Kutuzov, V.N. Mikhalenko, M.S. Sudakova, A.V.Kozachek Пространственно-временная изменчивость снегонакопления на западном плато Эльбруса (5100 м над ур. моря), Центральный Кавказ по данным высокочастотной радиолокационной съёмки Лед и Снег, - (year - 2022)

2. Mikhalenko V.N., Kutuzov S.S., Lavrentiev I.I., Toropov P.A., Vladimirova D.O., Abramov A.A., Matskovsky V.V. Гляциоклиматические исследования Института географии РАН в кратере Восточной вершины Эльбруса в 2020 г. Лед и Снег, Т. 61, вып. 1, с. 149-160 (year - 2021) https://doi.org/10.31857/S2076673421010078

3. Batalova V., Mikhalenko V., Kutuzov S., Shumilovskikh L., Shukurov K. Modern atmospheric monitoring using pollen analysis of ice cores: a case study from the Elbrus Western Plateau, Caucasus, Russia EGU, 19-30 (year - 2021) https://doi.org/10.5194/egusphere-egu21-8202

4. Kutuzov S., Mikhalenko V., Lavrentiev I., Toropov P., Vladimirova D., Abramov A., Matskovsky V. A new ice core from the Eastern Summit of Mt. Elbrus, Caucasus, Russia EGU, EGU21-5973 (year - 2021) https://doi.org/10.5194/egusphere-egu21-5973

5. Batalova V.A. Палинологические спектры ледниковых кернов Западного плато Эльбруса как региональный индикатор атмосферного переноса микрочастиц Материалы Международного молодёжного научного форума «ЛОМОНОСОВ-2021», с. 7-12 (year - 2021)

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Annotation of the results obtained in 2020
Observations of the meteorological regime and the heat balance of the glacier were made, radar survey of ice thickness and seasonal snow cover was carried out, a borehole was drilled from surface to bedrock, an ice core was obtained 96.01 m long, temperatures in the borehole were measured, samples were taken from the seasonal snow depth in the snow pit for isotopic, chemical and spore-pollen analyzes, gas samples were collected on the surface of the fumarole field and in the atmosphere above the glacier, monitoring of the soil temperature at the fumarole site, which began in 2013, was continued in the period from 18 to 30 August in the crater of the Eastern Summit at an altitude of 5600 m above sea level. The temperature on the glacier bedrock was -0.6 ° С. At depths from 20 m to the glacier bed, the temperature change is almost linear, which indicates a steady state heat transfer and makes it possible to determine the magnitude of the heat flow. The value of the heat flux density at the measurement point was calculated, equal to 0.39 W / m2. The maximum ice thickness was measured as 96 m. The ice volume is 3 million m3. Based on the radar data and a digital elevation model constructed from the results of the UAV survey, maps of the surface height, ice thickness and the relief of the subglacial bed for the crater of the Eastern Summit of Elbrus were created. A high-frequency (1400 MHz) GPR was used for the first time to perform spatial radar surveys of the thickness of the snow-firn strata. Meteorological observations at the Eastern Summit were carried out from 20 to 30 August 2020. The synoptic situation during the measurement period was characterized by two typical synoptic processes: in the period from 20 to 24 August - an Atlantic-type cyclonic process, 25 - 30 August - an anticyclonic process of the Azores type. It was found that the amplitude of synoptic scale fluctuations exceeds the amplitude of the daily variation of the main values of temperature, wind speed, humidity); high values of the average and maximum wind speed were noted, associated with the passage of atmospheric fronts, the transfer of the kinetic energy of the jet stream from the upper troposphere to the middle one, as well as with the effects of leeward storms; high temporary variability of relative humidity and a large deficit of humidity in cloudless conditions, which contributes to intensive evaporation and sublimation from the snow surface. A method for assessing the orographic component of the condensation rate and water content of clouds based on the ERA5 reanalysis data has been developed. It is based on the calculation of the condensation rate from temperature, water vapor partial pressure and wind speed at standard isobaric levels. This scheme is a synthesis of the Clausius-Clapeyron equation with an orographic correction of the vertical velocity component, which is calculated from the continuity equation for an incompressible fluid. The model is implemented for different altitude levels on Elbrus. Sampling of atmospheric precipitation samples at the Azau glade in the Elbrus region continued. During the year, samples were taken of all precipitation in the period from 09/10/2019 to 06/18/2020. A selection was made in the crater of the Eastern Summit of Elbrus at an altitude of 5600 m. Based on a mathematical model of ice flow, the fields of velocity, pressure, and age of firn / ice were calculated in the entire volume of the glacier on the Western Plateau of Elbrus. The main result of the 2020 work on this section of the project is the transition from a one-dimensional firn / ice dating model to a three-dimensional one. The analysis of the Elbrus glacial core in 2018 for the content of stable oxygen and hydrogen isotopes was continued. All isotopic data were compared for cores from 2009 and 2017 and 2018. A spore-pollen analysis of a 24-meter firn core obtained on the Western plateau in 2017 was carried out. The palynological analysis showed that the spore-pollen spectra of the Elbrus glaciers differ in taxonomic diversity - 29 taxa of higher plants, 5 spore plants, 7 varieties of fungi were found in the samples. 1 genus of shell amoebae, spherical black carbon and micron. Preliminary data on the multi-seasonal regime of plant dusting allow us to conclude that the seasons are characterized by quantitative and qualitative differences in the concentration of microfossils. The spore-pollen spectra of the Elbrus glaciers are characterized by seasonal heterogeneity and significant taxonomic diversity and are represented mainly by local species of the Caucasus. In 2020, in ice-core samples from Elbrus (2009), the content of polycyclic aromatic hydrocarbons (PAHs), which are formed as a result of industrial production and combustion of fossil fuels, as well as on fragrances (fragrances), widely used in personal care products, were analyzed. In order to calibrate the absolute methane values obtained from the 2009 core, air samples were collected in the crater of the Eastern summit of Elbrus and along the altitude profile of the Garabashi glacier. In total, 29 air samples were taken at altitudes of 3387-5598 m above sea level. The methane concentration will be measured by the end of 2020 by gas chromatography, and the data obtained will be used to calibrate the absolute values of the methane series over the past two centuries using data from the Elbrus glacial core. Monitoring of soil temperature on the surface of the fumarole field and at depths of 40 and 80 cm from the surface on the outer crater rim of the Eastern Summit of Elbrus continued. Comparison with the results obtained in 2013-2015 showed the stability of the temperature regime.

Publications

1. Chernyakov G.A., Vitelli V., Alexandrin M.Y., Grachev A.M., Mikhalenko V.N., Kozachek A.V., Solomina O.N., Matskovsky V.V. Dynamics of seasonal patterns in geochemical, isotopic, and meteorological records of the Elbrus region derived from functional data clustering Geography, Environment, Sustainability, 13(3), 68-75 (year - 2020) https://doi.org/10.24057/2071-9388-2019-180

2. Dumont M., Tuzet F., Gascoin S., Picard G., Kutuzov S., Lafaysse M., Cluzet B., Nheili R., Painter T.H. Accelerated Snow Melt in the Russian Caucasus Mountains After the Saharan Dust Outbreak in March 2018 Journal of Geophysical Research: Earth Surface, 125, e2020JF005641 (year - 2020) https://doi.org/10.1029/2020JF005641

3. Tyuflin S.A., Nagornov O.V., Chernyakov G.A., Mikhalenko V.N., Toropov P.A., Kutuzov S.S. Реконструкция температуры деятельного слоя ледника на Западном плато Эльбруса за 1930–2008 гг. Лед и Снег, 60)4), 485-497. (year - 2020) https://doi.org/10.31857/S2076673420040054

4. Vecchiato M., Gambaro A., Kehrwald N.M., Ginot P., Kutuzov S., Mikhalenko V., Barbante C. The Great Acceleration of fragrances and PAHs archived in an ice core from Elbrus, Caucasus Scientific Reports, 10, 10661 (year - 2020) https://doi.org/10.1038/s41598-020-67642-x

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