Известия Томского политехнического университета: Инжиниринг георесурсов (Jun 2023)
STABLE ISOTOPES OF HYDROGEN, OXYGEN AND CARBON WHEN INTERPRETING FORMATION CONDITIONS OF SURFACE WATER BODIES OF YAMALO-NENETS AUTONOMOUS REGION
Abstract
Link for citation: Lepokurova O.E., Ivanova I.S., Pyrayev A.N. Stable isotopes of hydrogen, oxygen and carbon when interpreting formation conditions of surface water bodies of Yamalo-Nenets autonomous region. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 6, рр.7-19. In Rus. The relevance. Stable isotopes are widely used in geochemistry for solving various genetic problems, which is associated with the assumption of the constancy of the original isotopic composition of any element, subsequently changed under the influence of various processes. In the practice of surface water studies, isotope methods are used for solving not only direct genetic problems, but also for various related problems. In arctic regions affected by permafrost, water isotopes are increasingly being used to assess the contribution of melt water to the balance of total river flow, especially in conditions of accelerated melting, which leads to changes in the hydrological regime and the overall structure of the landscape. The analysis of the isotope composition of dissolved inorganic carbon is of particular research interest, since it gives an idea of the participation of organic matter released during the thawing of permafrost peat in isotope exchange with water. The joint use of the chemical and isotopic characteristics of water bodies will make it possible to study in detail the genesis, features of the formation and interaction of these waters with the environment. The main aim: clarification of the genesis and conditions of formation of surface water bodies in the Arctic regions of Western Siberia, subject to the influence of permafrost, using the composition of stable isotopes H, O, C. Objects: surface water bodies of the tundra and forest-tundra natural zones of the Yamalo-Nenets Autonomous Region. Field work took place in August 2020. Water samples for the isotopic composition were taken from three large rivers – Ob, Taz, Pur, and in the right tributary of Pur River – Ngarka-Khadytayakha, 7 large lakes (from 2500 to 300000 m2), 1 small thermokarst lake (12 m2) and from 3 depressions (the initial stage of formation of thermokarst lakes); and 2 soil cross sections. A total of 17 water samples. In addition, 5 peat samples were taken from one soil cross section from five depth intervals up to 55 cm. Methods. Chemical composition of water was analyzed by standard methods (titration, inductively coupled plasma mass spectrometry, photometry, ion chromatography and high-temperature catalytic oxidation method) at the Problematic Research Laboratory of Hydrogeochemistry of Tomsk Polytechnic University. The study of the isotopic composition of oxygen, hydrogen and carbon of water-dissolved carbon dioxide was carried out in the Analytical Center for multi-elemental and isotope research SB RAS using Isotope Ratio Mass Spectrometer FinniganTM MAT 253 equipped by H/Device and GasBench II for sample preparation. Results. Isotope composition of oxygen, hydrogen and carbon in waters and dissolved inorganic carbon for surface waters of the tundra and forest-tundra zones of the YaNAO are presented. It is shown that each object (soils, depressions, lakes and rivers) is characterized by individual intervals of δD, δ18О, δ13С (dissolved inorganic carbon) values, which indicates different specifics of their formation and allows them to be differentiated. Comparison with the already available data on δD, δ18O of atmospheric precipitation, surface water and snow in the region revealed that river and soil waters, in comparison with other water bodies, were formed in colder conditions. The δ13CDIC values indicated the presence of two sources of carbon in the surface waters of the region: biogenic (light) and soil diffusion, which inherits the isotopic composition of the atmosphere (heavy). The first one is dominates in soil waters, depressions, shallow lakes and, apparently, in stagnant river waters. In large lakes and in the active course of the river, soil diffusion CO2 is more pronounced. The effect of permafrost thawing in the region is demonstrated by lighter δD and δ18O values (thawed waters), as well as by lighter δ13СDIC values (additional biogenic carbon is released from soils and peat). A scheme of possible distribution and exchange of stable isotopes H, O and C in natural waters and dissolved inorganic carbon for investigated region was developed. The obtained results can be used for determining genesis of the region natural waters; for clarifying conditions of waters and dissolved inorganic carbon formation; for identifying permafrost degradation processes and evaluating its rate; for paleoclimate reconstructions etc.
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