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Project titleDust flux in Ciscaucasia for the last 250 ka: sources, accumulation rates, forcings
Project LeadKonstantinov Evgeny
AffiliationInstitute of Geography of the Russian Academy of Sciences,
|Implementation period||07.2021 - 06.2024|
Research area 07 - EARTH SCIENCES, 07-701 - Paleogeography
KeywordsMineral dust, loess, paleosols, Pleistocene, Holocene, aeolian processes, OSL, paleoclimate, droughts, dust storms, Ciscaucasia
Mineral dust aerosol is correlated with the climate's condition on the Earth in general and specific planet's regions. The dust accumulation in environmental paleoarchives (loess, lacustrine, glacial) reflects the intensity of aeolian processes and the climate's humidity. In the south of European Russia, in the Ciscaucasia, there are vast areas of loess deposits that continuously cover the territory from the Sea of Azov to the Caspian Lowland. The Ciscaucasian loess formation generated by the mineral dust sedimentation over the past 500-800 thousand years. The total thickness of these deposits can reach 150-200 meters, and the thickness of the Upper Pleistocene loess in the east of the region reaches 50 meters, which is a record for European loess. Such high sedimentation rates make it possible to provide highly detailed paleoreconstructions based on serial luminescence dating and lithological and geochemical analyses complex use. But the composition of loess and its thickness is heterogeneous across the territory. This heterogeneity is the key to understanding the sources of dust (areas of deflation). It can be sandy alluvial massifs of large rivers' lower reaches (Volga, Don, Terek and Kuma) and sea terraces. The scientific significance of the project is determined by the international scientific community's broad interest in the sources and volumes of mineral dust entering the atmosphere during the end of the Quaternary period. Quantitative regional assessment of the rate of mineral dust intake is an essential link in the chain of paleoclimatic reconstructions. It serves as an indicator of the climate aridization extent. Much attention in the scientific literature of the last two decades is paid to the atmospheric circulation reconstruction, the direction and strength of paleowind based on studies of mineral dust transport routes. Regarding regional paleogeography, it seems to be of great interest to extract the following information of significant changes in the hydro-climatic characteristics of the East European plain out of the loess-paleosol series: the area of the glacier cover, the river flow volume, the average annual precipitation and evaporation, the Caspian and Black Seas' levels. Stratigraphically, the loess-paleosol series of the Ciscaucasia (especially the central and eastern territories) can claim the role of regional stratotype sections for the Middle and Late Pleistocene. The high risks to agriculture, life and health of people in densely populated areas of the south of Russia, associated with soil erosion and dust accumulation processes, determine the project's practical significance. The study of the mechanisms of these processes' reaction to global and regional climate changes will allow us to make more reasonable long-term forecasts of the rate of deflation and aeolian accumulation, the deflation areas localization, and dust storms intensity and frequency. Besides, reliable paleoreconstructions based on the sedimentary paleoarchives study will verify existing paleoclimatic models, contributing to their qualitative improvement. During the project realization, we plan to study the structure, material composition and precise age of the loess-paleosol series in the interval of the last 250 thousand years at seven key sites on the west, central, and east parts of the region. Luminescent dating of the samples (at least 7 per site) and a series of lithological and geochemical studies of samples taken at least every 10 cm are supposed to get done. For Holocene loess in the east of the region, the detail of testing in cores suppose to be every 2 cm. The study of lake-marsh paleoarchives will support the identification of extreme Holocene aeolian events. As a result of the study, we suppose to calculate the dynamics of loess accumulation rates at different stages, determine the sources of dust, identify regional litho-geochemical markers, clarify and detail the scheme of loess-paleosol stratigraphy, link the history of loess accumulation with paleogeographic events in marine basins, correlate with global scales, and verify existing paleoclimatic models.
1. Determination of the aeolian dust main sources (deflation areas) forming the loess cover of the Ciscaucasia. Identification of changes in the contribution of various sources for the main warming periods (thermochrons) and cooling periods (cryochrons) of the end of Middle-Late Pleistocene and Holocene. 2. Loess accumulation rate calculation over the last 250 thousand years for the Western, Central and Eastern Ciscaucasia. Spatial reconstruction of the mass accumulation rate (MAR) for the main stages of the claimed interval. Extreme aeolian regional events' identification based on lithological features in loess and lacustrine paleoarchives. 3. Detailed chronostratigraphic scheme of loess-soil series in the south of Russia for the last two climatic macrocycles. Correlation with global and regional stratigraphic scales. 4. Splitting of local, regional and global signals in the Ciscaucasian loess-soil series by comparing the records with each other, and with regional loess stratotype sections of Central and South-Eastern Europe, as well as with global data (GRIP/NGRIP δ180; GRIP/NGRIP concentration of dust particles and Ca2+; and generalized marine isotope scale LR-04). 5. Determination of the leading factors influencing the rate and particle-size composition changes of mineral dust entering the Ciscaucasia plains. Reconstruction of the prevailing directions and strength of the surface wind, the climate humidity and dust storms intensity for the main climatic extremes over the past 250 thousand years. Characterization of the connection between loess accumulation and regional hydrological dynamics: modelled fluctuations of the Azov, the Black Sea and the Caspian basins' levels and changes in the river flow volume. 6. The paleoclimatic models verification. Comparison of paleoreconstructions of climatic parameters based on numerical modelling with paleoreconstructions based on sedimental paleoarchives analytics. The claimed results scientific significance is determined by the international scientific community's broad interest in the sources and volumes of mineral dust entering the atmosphere during the end of the Quaternary period. Many works are devoted to the climate moisture history and the spatial redistribution of arid and humid land zones on a global climate change background. The quantitative regional assessment of mineral dust mass accumulation rate (MAR) is an essential link in the chain of paleoclimatic reconstructions. It serves as an indicator of the climate aridization degree. Much attention in the scientific literature of the last two decades is paid to the reconstruction of atmospheric circulation, the direction and strength of paleowinds based on studies of the mineral dust transport direction. As for the regional paleogeography, it is important to record the hydro-climatic characteristics of significant changes on the East European Plain in the loess-soil series: the glacial cover area, the river flow volume, the average annual precipitation and evaporation, and the level of the Caspian and Black Seas. Stratigraphically, the loess-soil series of the Ciscaucasia (especially in the central and eastern areas) can claim the Middle and Late Pleistocene regional stratotype sections' role. The thickness and undamaged condition of the Ciscaucasian loess paleoarchives is the highest in Europe. It is obtaining a record with a very high time resolution - hundreds of years. The high risks to agriculture, life, and health of people in densely populated areas of the Russian south, associated with soil erosion and dust accumulation, determine the study results' practical significance. The study of these processes' reactions to global and regional climate changes will allow us to make more reasonable long-term forecasts of the deflation and aeolian accumulation rates, the localization of deflation areas, and the intensity and frequency of dust storms. Also, reliable paleoreconstructions based on the sedimental paleoarchives study will verify existing paleoclimatic models, contributing to their qualitative improvement.
Annotation of the results obtained in 2021
Completed works During the reporting period, fieldwork was carried out to study the structure of the Upper Pleistocene and Holocene loess-paleosoil series of Ciscaucasia. The work included core drilling, description of sections, and sampling in the following areas: Stepnoe (Stavropol Territory), Ust-Labinsk (Krasnodar Territory), Mikhailovskoye (Rostov Region), Temizhbekskaya (Krasnodar Territory). Reference samples of alluvial and eolian sands were taken for lithological and geochemical studies to search for potential mineral dust sources. The joint laboratory of OSL dating of Moscow State University and the Institute of Geography RAS performed luminescence dating of 10 samples from the Temizhbekskaya section. Together with the earlier datings, this made it possible to build a reliable age model for the Temizhbekskaya section. Sixteen samples from the OT-20 well (Otkaznoye) and ten samples from the U-Lab well (Ust-Labinsk) underwent preliminary preparation. A series of lithological and geochemical studies was performed for Otkaznoye-2020, Stepnoe, Temizhbekskaya, Pyatiletka, Ust-Labinsk, Mikhailovskoye cores: granulometric analysis, determination of the content of organic matter and carbonates, magnetic susceptibility, the frequency dependence of magnetic susceptibility, color measurement, bulk chemical analysis. The results of climate modelling of the PMIP4 project were used to analyze the influence of climatic conditions on dust emission for the following periods: the last glacial maximum (LGM, 21 ka), the Holocene optimum (midHolocene, 6 ka), the Mikulin interglacial (lig127k, 127 ka). The results of paleoexperiments were compared with a control experiment on the reproduction of the preindustrial climate (piControl). The results of two models INMCM and MIROC were analyzed. Model changes in the intensity of dust sources were considered. These data reflect the climatic conditions of dust formation - predominantly humid conditions. Meteorological data were analyzed, including wind direction and speed and their relationship to dust storms. Data were received from the All-Russian Research Institute of Hydrometeorological Information - World Data Center (VNIIGMI-MCD) website. Data have been received from 7 weather stations in Ciscaucasia since 1966. Wind roses have been constructed that takes into account wind directions at any speed, with a speed of more than 10 m/s (wind speed capable of carrying the sand fraction) and during dust storms. During the reporting period, project members took part in three Russian conferences, where they made oral presentations on the project results. Three articles were submitted and accepted for publication. All articles will be published in journals indexed in WoS and/or Scopus. Main scientific results It has been established that three phases of soil formation are distinguished in the structure of the Mezin pedocomplex in all upland areas. The Bryansk interval is much less expressed; it is often enormously extended and has 2-3 independent subphases of embryonic soil formation. In almost all studied LPSs, two noticeable peaks of sand are distinguished, which correspond to the beginning of MIS 2 and MIS 5b. The Kuban LPS are distinguished by a characteristic pattern of changes in particle size distribution with depth; the main feature is a sharp increase of the sand content in MIS 2 - MIS 1. There is a strongly marked relationship between the content of the sand fraction in the loess and the distance to the massifs of alluvial sands and sandy loams, the main of which are located in the east Caspian lowland and on the terraces of the Don and Kuban rivers. An anomalously high thickness of Upper Pleistocene and Holocene LPS is observed in the Stepnoe area. Thus, according to preliminary estimates, more than 23 m of loess-like sandy loam has accumulated in Stepnoe over the past 60 thousand years. Holocene loess thickness can exceed 3 m in this area. The results of luminescent dating of the Temizhbekskaya section made it possible to estimate the age of the LPS above volcanic ash layer (Upper Pleistocene), volcanic ash layer (~220 ka), and loess-like loam strata under volcanic ash layer (230–260 ka). Based on our own and published materials (data on the structure of the LPS in 25 controversial sections and boreholes of Ciscaucasia), the average sedimentation rates for stratigraphic units of the Upper Pleistocene were calculated. The collected data conclude that the loess accumulation rates are related to the distance to the sandy massifs undergoing deflation. Moreover, the area of these deflation areas (sources of mineral dust) correlates with the average loess accumulation rates in the adjacent loess-paleosol series. In terms of time, there is a clear division according to the average sedimentation rate. In cryochrones MIS 4 and MIS 2, the average rates of loess accumulation throughout Ciscaucasia were 1.5 and 2.5 times higher, respectively, than the average rates established for thermochrones (MIS 5, MIS 3, and MIS 1). A spatial analysis of the structure and composition of the loess cover showed that the Caspian lowland has been and remains the dominant source of mineral dust for the territory of Ciscaucasia over the past 130 thousand years. Massifs of sandy and sandy loam deposits formed by the alluvium of the Terek, Kuma and Volga rivers are deflated by strong easterly winds in the arid climate, and masses of mineral dust are transported far to the west up to the Sea of Azov. The content of the sandy fraction in loess and the average rate of loess accumulation naturally decreases from east to west, from the Terek-Kuma lowland to the Sea of Azov. Terraces and alluvial estuarine plains of the Don and Kuban rivers are secondary sources of mineral dust, increasing the content of the sand fraction in loess and the rate of loess accumulation in the areas adjacent to the valleys. Based on the results of model experiments, it is shown that the general localization of the main sources of mineral dust has not changed dramatically in the studied region over the past 130 thousand years. The intensity of dust formation in warmer epochs was generally lower than in cold ones. At the same time, when comparing experiments on the INMCM and MIROC models, significant differences in dust emission volumes are revealed, which are probably associated with differences in the boundary conditions of model experiments and with a low spatial resolution of the models. Archival meteorological data show that the western and eastern wind directions are predominant for all the considered meteorological stations of Ciscaucasia. The northern and southern winds share does not exceed 10-20%. During dust storms, the east wind direction sharply prevails, more than 80%. Based on the data obtained, it can be concluded that the transport of mineral dust from east to west dominates in dust storms.
1. Konstantinov E.A., Mazneva E.A., Sychev N.V., Zakharov A.L., Filippova K.G. Variability in the structure and composition of the Upper Quaternary loess of Ciscaucasia (south of the European part of Russia) Geomorfologiya, - (year - 2022)
2. Konstantinov E.A., Zakharov A.L., Sychev N.V., Mazneva E.A., Kurbanov R.N., Morozova P.A. LOESS ACCUMULATION IN THE SOUTH OF THE EUROPEAN PART OF RUSSIA AT THE END OF THE QUATERNARY Herald of the Russian Academy of Sciences, - (year - 2022)
3. N. V. Sychev, E. A. Konstantinov, A. L. Zakharov, M. Frechen, S. Tsukamoto New Data on Geochronology of the Upper Quaternary Loess–Soil Sequence in the Terek–Kuma Lowland Lithology and mineral resources, - (year - 2022)
4. N.V. Sychev, E.A. Konstantinov, A.L. Zakharov, E.A. Mazneva, M. Frechen, S. Tsukamoto, N.V. Karpukhina НОВЫЕ ДАННЫЕ ПО ГЕОХРОНОЛОГИИ ВЕРХНЕЧЕТВЕРТИЧНЫХ ЛЕССОВ ТЕРСКО-КУМСКОЙ НИЗМЕННОСТИ Сборник Пути эволюционной географии – 2021. Выпуск 2. Материалы II Всероссийской научной конференции, посвященной памяти профессора А.А. Величко (Москва, 22-25 ноября 2021 г.), место издания ИГРАН Москва, Выпуск 2. Материалы II Всероссийской научной конференции, посвященной памяти профессора А.А. Величко. с.381-383 (year - 2021)
Annotation of the results obtained in 2022
During the second year of the project implementation, field work was carried out in eight key areas of Ciscaucasia in order to obtain materials on the structure and composition of the Upper Quaternary loess-soil series (LPS). During the work, drilling with core sampling, clearing of outcrops and pitting, description and documentation of cores and section walls, sampling for luminescence dating, lithological and geochemical studies, petro- and paleomagnetic studies, paleosol studies were carried out. Preliminary results of luminescence dating of a new series of 16 samples for core OT-20 (Otkaznoe plot) were obtained. The dates confirm the Upper Pleistocene age of the exposed LPS and detail the earlier stratigraphic subdivision scheme. At the Otkaznoye site, in three mine workings at the level of the Krutitskaya paleosol (MIS 5c), previously unexposed volcanic ash was found, dispersed in the loess. In terms of its stratigraphic position, the ash presumably corresponds to the Elbrus tephra described in the core from the Sarmatskaya well (SARM) in the bottom sediments of the Caspian Sea, the age of which is estimated at 84.6±7.4. For the first time, the structure of the Mezin pedocomplex (MIS 5), which was previously available only in well cores, was uncovered for the Otkaznoye site in clearing. On the basis of morphological and micromorphological features, the Krutitsa (MIS 5c) and Salyn paleosols (MIS 5e) were diagnosed. The Krutitskaya paleosol belongs to Calcic Gypsic Kastanozem Cambic Siltic Tephric according to the international classification WRB (2015). The Salyn soil was defined as Calcic Gypsic Kastanozem Siltic Cambic and is similar to the modern Holocene soil. The Salyn soil was formed under alternating wet and arid conditions, as evidenced by the abundance of carbonate nodules and large ferruginous-manganese nodules and spots. As a result of the petro- and paleomagnetic study of the loess-soil series in two sections (OT-22R and OT-22Sh2) at the Otkaznoye site, it was found that the prevailing direction of paleowinds in the study area at the beginning of the Late Pleistocene was ESE–WNW. During the first paleomagnetic studies in the sections, it was not possible to reveal the excursion of the Blake geomagnetic field expected for this time interval (~120 ka), which may be due to the peculiarities of the paleomagnetic record in the loess-soil deposits of the region or partial erosion of the sedimentary sequence and requires more detailed research. An analysis of the array of geochemical data showed that the loesses of Ciscaucasia have a very similar, predominantly granodiaritic composition, enriched in carbonates and clay. They were significantly altered by weathering processes prior to eolian sedimentation. Reliable geochemical trends indicating the sources of aeolian material have not yet been identified. Age models of sedimentation and maps visualizing the change in sedimentation rates and sand content in LSL were constructed for the main thermo- and cryochrons of the late Pleistocene and Holocene. From these results, it can be seen that the content of the sand fraction in loess and the average rate of loess accumulation naturally decrease from east to west, from the Tersko-Kuma lowland to the Sea of Azov. In loess formed during cryochrons (MIS 4 and MIS 2), the sand content is on average 1.3 times higher than in loess of thermochrons (MIS 5, MIS 3 and MIS 1). It is confirmed that the Caspian lowland has been and remains the dominant source of mineral dust for the territory of Ciscaucasia over the past 130 thousand years. In the Caspian Sea, massifs of sandy and sandy loam deposits in an arid climate are blown away by strong easterly winds. The wind carries masses of mineral dust far to the west up to the Sea of Azov. The terraces and alluvial estuarine plains of the Don and Kuban are secondary sources of mineral dust, increasing the content of the sand fraction in the LPS in the territories adjacent to the valleys. The results of comparison of reference sections of the Late Quaternary LPS of the Ciscaucasia with global and regional indicators of paleoclimate allow us to draw the following preliminary conclusions: 1) changes in sedimentation rates and average sizes of loess particles are generally consistent with changes in climate humidity in Europe and the extratropical space of the Northern Hemisphere; 2) the likely leading factor influencing the change in the rate of accumulation of mineral dust is the degree of aridity in the areas of deflation - the Caspian region; 3) the second most important factor influencing the intensity of loess accumulation is the degree of development of the vegetation cover in the areas of accumulation of mineral dust; 4) Fluctuations in the level of the Caspian Basin are a secondary factor in the accumulation of loess even in the eastern regions of the distribution of the LPS of Ciscaucasia.
1. Konstantinov E.A., Zakharov A.L., Sychev N.V., Mazneva E.A., Kurbanov R.N. Late Quaternary loess in the Ciscaucasia (South of Russia): distribution, composition, and source of mineral dust Abstracts of The 2022 INQUA LoessFest, Yang SL, (ed.), 2022. Abstracts of The 2022 INQUA LoessFest, Beijing, China. Online only (year - 2022)
2. Sychev N.V., Konstantinov E.A., Zakharov A.L. Аккумуляция эоловых лессов Предкавказья в голоцене Динамика экосистем в голоцене. Сборник статей по материалам всероссийской научной конференции, Санкт-Петербург, 17–21 октября 2022 года / отв. ред. Д. А. Субетто. — Санкт-Петербург : Изд-во РГПУ им. А. И. Герцена, 2022. — 516 c., Сборник статей по материалам всероссийской научной конференции, Санкт-Петербург, 17–21 октября 2022 года / отв. ред. Д. А. Субетто. — Санкт-Петербург : Изд-во РГПУ им. А. И. Герцена, 2022. С. (year - 2022)
3. Sychev N.V., Konstantinov E.A., Zakharov A.L., Mazneva E.A., Frechen M., Tsukamoto S. Люминесцентная геохронология лёсcов центрального Предкавказья Институт географии РАН, сборник доступен только онлайн, Сборник тезисов второй всероссийской научной конференций "Геохронология четвертичного периода: инструментальные методы датирования новейших отложений". Москва 19-22 апреля 2022 года. С. 75-76. (year - 2022)