Carbon-to-nitrogen ratio in late Pleistocene ice wedges and in modern soils in the Batagay megaslump, north of Yakutia

Vasil'chuk Alla Constantinovna Doctor of Geography Leading Research Fellow, Laboratory of Geoecology of the Northern Territories, Faculty of Geography, Lomonosov Moscow State University 119991, Russia, g. Moscow, Leninskie Gory, GSP-1, 1,, geograficheskii fakul'tet, NIL geoekologii Severa alla-vasilch@yandex.ru Other publications by this author     Vasil'chuk Yurii Kirillovich ORCID: 0000-0001-5847-5568 Doctor of Geology and Mineralogy Professor, Department of Landscape Geochemistry and Soil Geography, Faculty of Geography, Lomonosov Moscow State University 119991, Russia, Moskva oblast', g. Moscow, ul. Leninskie Gory, 1, of. 2009 vasilch_geo@mail.ru Budantseva Nadine Arkad'evna ORCID: 0000-0003-4292-5709 PhD in Geography Senior Researcher, Department of Landscape Geochemistry and Soil Geography, Faculty of Geography, Lomonosov Moscow State University 119991, Leninskie Gory, 1, office 2007, Moscow, Russia nadin.budanceva@mail.ru Vasil'chuk Jessica Yur'evna ORCID: 0000-0002-4855-8316 Junior Researcher, Department of Landscape Geochemistry and Soil Geography, Faculty of Geography, Lomonosov Moscow State University 119991, Russia, Moskva oblast', g. Moscow, ul. Leninskie Gory, 1, of. 2007 jessica.vasilchuk@gmail.com Ginzburg Alexander Pavlovich Master's Student, Department of Landscape Geochemistry and Soil Geography, Faculty of Geography, Lomonosov Moscow State University 119991, Russia, Moskva oblast', g. Moscow, ul. Leninskie Gory, 1, of. 2007 alexandrginzburg13154@yandex.ru Bludushkina Lyubov' Bakhtiyarovna ORCID: 0000-0003-2422-8790 Junior Researcher, Department of Landscape Geochemistry and Soil Geography, Faculty of Geography, Lomonosov Moscow State University 119991, Russia, Leninskie Gory 1 oblast', g. Leninskie Gory 1, ul. Leninskie Gory, 1, of. 2007 bludushkina19@mail.ru

Slyshkina Elena Sergeevna Head of the Laboratory, JSC Atomenergoproekt 119234, Podol'skikh Kursantov str., 1, office 250, Moscow, Russia lena.slyshkina@gmail.com Other publications by this author

Introduction

The objective of this study is to analyze the carbon and nitrogen content, as well as the ratio of these elements in the genetic horizons of the soil cover, edom deposits and syngenetic re–vein ice (PGL) of the upper edom complex ^[1] of the Batagai mega-ravine (67°34'49" s.w., 134°46'19" vd., 10 km south-east of the village . Batagai, Verkhoyansky ulus, Republic of Yakutia SAKHA) in the basin of the Yana River. The ravine is located on the southeastern slope at the foot of Mount Kirgilyakh (Fig. 1). The length of the ravine according to the results of measurements in 2019 is 2.29 km, and the width is 1 km ^[2]. The height difference between the highest and lowest points of the mega ravine is 92 m, the central wall of the outcrop has a height of 55 m ^{[3, 4]}. The western side of the ravine is located higher up the slope at an absolute height of 325 m, and the eastern side is located at an absolute height of 287 m.

The nitrogen and carbon content is one of the basic characteristics of organic matter. The authors studied the soils in the vicinity of the Batagai mega-ravine, syngenetic re-vein ice and the Batagaika sediments containing them. Previously, a large array of data on the carbon and nitrogen content in the sediments of the ice complex was accumulated, but there are practically no such definitions in the re-vein ice. These indicators are important for assessing the state of organic matter trapped in re-vein ice. The authors obtained data on the carbon and nitrogen content in ice veins at different levels of the upper edom complex. 

According to the Batagai weather station, the climate of the territory is moderately cold. The average annual air temperature is negative -14.8 °C. The average air temperature in July is +15.5 °C, the average air temperature in January is -44.7 °C. The difference between the values of the summer maximum temperature of +37.3 °C and the minimum winter temperature of -67.8 °C is 105.1 °C.

Fig. 1. Batagay megaovrag (photo from the website https://magmadergisi.com/doga/buyuyen-krater-batagayka ), the arrows show the location of the ice veins, the results of the study of which are presented in this study

The territory is located in the area of continuous permafrost distribution, the average annual soil temperature at a depth of zero annual amplitudes is -5.5 °C - -8.0 °C. The layer of seasonal thawing varies from 0.2-0.4 m under the forest to 0.4-1.2 m in open areas. Cryogenic processes are widespread: thermokarst, thermal erosion, solifluction, weathering, frost cracking, etc.

Vegetation of the north taiga and forest-tundra type, dominated by Kayander larch, birch (Betula middendorffii), dwarf birch, as well as cedar elderberry, alder, bagulnik, willow, weeping willow, aspen, among herbaceous plants are often found lapchatka, mother and stepmother, dandelion, snowdrop, raspberry, rosehip, uohta (wild currant), knyazhenika, cranberries, blueberries, etc.

In the area of the village . Tundra podburas, podzols, tundra coarse-humus fragmentary, as well as alluvial soils are common in Batagai. The authors studied the soil profiles revealed in the vicinity of the Batagai ravine-crater. The studied soils belong to the illuvial-ferruginous permafrost light-earths and post-pyrogenic permafrost illuvial-ferruginous podzols. The structure of soil profiles includes horizons O – BF – C1f – C2fp – C3 – CRMfp – C4 (section B-VG-2019/1) and Opir– E – BHF – C1 – C2 (section B-VG-2019/3).

Research methods

Ice cores were selected using BOSCH GSR 18V-EC TE and Makita DDF481RTE 188 cordless drills with specially made titanium nozzles. Samples were taken with a minimum step of 0.1-0.3 m both vertically and horizontally. During the selection, the axial part of the ice vein was determined. In order to exclude contamination with modern organic material, the outer 5-10 cm of ice was removed before sampling.   Each ice sample was washed with meltwater obtained at the initial stage of melting from this sample. The host deposits were taken from the frozen wall with preliminary removal of the outer 5-10 cm layer. The determination of the altitude marks of the studied objects was carried out using a laser rangefinder Leica DISTO 5910. Sample preparation of samples included drying soil and organic inclusions from ice veins containing sediments and soils, and grinding them with a rubber pestle in an agate mortar. The carbon and nitrogen content was analyzed in soil and re-vein ice samples using the VARIO EL III V4.01 20.Aug. 2002 elemental CHNS analyzer, Elementar Analysensysteme GmbH, Germany. The accuracy is 0.1% of the absolute value with simultaneous determination of CHNS in 2 mg of sulfanylic acid; the relative error is less than 0.2%. The molar ratio C/N is calculated from the results of determination of carbon and nitrogen included in the sample.

Results and discussion

To study the carbon and nitrogen content, ice veins of the first and second tiers of the upper edom complex were tested: PZHL-2 (altitude interval 260-252 m); PZHL-3 (altitude interval 320-315 m); PZHL-5 (altitude interval – 273-266 m); PZHL-6 (altitude interval – 305-273 m) (see Fig. 1). Ice veins PZHL-5 and PZHL-7 are exposed within the eastern side of the ravine, PZHL-3 in a second-order ravine in the central part of the outcrop, PZHL-6 and PZHL-2 are opened in the main wall.  For comparison, the carbon and nitrogen content was determined in the studied soil sections near the town of Kirgily, as well as in the sediments of edoma containing re-vein ice.

According to the results of radiocarbon dating of ice veins, all are dated to the Late Pleistocene ^[5]  The ice veins of PZHL-2, 5, 7 and the lower part of PZHL-6 belong to an older ice complex (50-46 cal. thousand years ago and older, and PZHL-3 and the upper part of PZHL-6 belong to a younger one (31 – 27 cal. thousand years ago).

The sediments containing re-vein ice (Fig. 2) on average contain 0.21 mol of carbon, the maximum value is 0.48 mol, the minimum is 0.09 mol, the average nitrogen content is 0.03 mol, the maximum is 0.05 mol, the minimum is 0.02 mol, the value of the C/N ratio varies from 5.01 to 9.46, averaging 6.77. The highest values of the carbon content and the C/N ratio were noted in the middle part of the section of the upper edom complex of Batagai at an altitude of 225 m above sea level.

Fig. 2. Variations of carbon (1), nitrogen (2) and C/N ratio (3) in the sediments of the upper edom complex

According to the studied soil sections in the vicinity of the Batagai section (Fig. 3), the following results were obtained for two types of soils. The average carbon content in the illuvial-ferruginous permafrost is 0.25 mol, the maximum value is 0.87 mol, the minimum is 0.04 mol, the average nitrogen content is 0.04 mol, the maximum is 0.08 mol, the minimum is 0.02 mol, the value of the C/N ratio varies from 1.09 in the parent rock to 11.67, averaging 4.01. Characteristics of the podzole and the lluvial-ferruginous post-pyrogenic permafrost differs significantly in carbon content, while the nitrogen content is about the same.  The average carbon content in is 0.08 mol, the maximum value is 0.21 mol, the minimum is 0.03 mol, the average nitrogen content is 0.04 mol, the maximum is 0.06 mol, the minimum is 0.03 mol, the value of the C/N ratio varies from 0.74 in the parent rock to 3.54, averaging 1.61.

Fig. 3. Variations of carbon (1), nitrogen (2) and C/N ratio (3) in the illuvial-ferruginous permafrost (A) horizons O – BF – C1f – C2fp – C3 – CRMfp – C4 (section B-VG-2019/1) and the illuvial-ferruginous postpyrogenic podzole Permafrost (B) Opir – E – BHF – C1 – C2 (section B-VG-2019/3)

Fig. 4. Variations of carbon (1), nitrogen (2) and C/N ratio (3) in the PZHL-2 ice 

         PLL 2 (Fig. 4) is characterized by stable values of carbon and nitrogen content:   the average carbon content is 0.16 mol, the maximum value is 0.23 mol, the minimum is 0.12 mol, the average nitrogen content is 0.03 mol, the maximum is 0.06 mol, the minimum is 0.02 mol, the value of the C/N ratio varies from 3.52 to 6.96, averaging 5.36. According to radiocarbon dating, this ice vein is older than 50 thousand. years, according to the results of isotope analysis, the most negative value of ?18 ^O is equal to -37.2 % ^[2].

 Fig. 5. Variations of carbon (1), nitrogen (2) and C/N ratio (3) in the PZHL-5 ice with depth

PLL 5 (Fig. 5) is characterized by significant fluctuations in the values of carbon and nitrogen content:   the average carbon content is 0.17 mol, the maximum value is 0.36 mol, the minimum is 0.10 mol, the average nitrogen content is 0.05 mol, the maximum is 0.09 mol, the minimum is 0.02 mol, the value of the C/N ratio varies from 2.38 to 6.53 averaging 4.25, there is a tendency to increase this indicator from the bottom up. According to radiocarbon dating, this ice vein was formed in the time interval 47.5 to 44.7 cal. thousand years ago ^[5].

Fig. 6. Variations of carbon (1), nitrogen (2) and C/N ratio (3) in the PZHL-6 ice with depth

The PZHL-6 ice vein has been tested in great detail. According to the results of the determination of the carbon and nitrogen content, it can be divided into two parts: 0.3-3.20 m and 3.60-28.2 m. In the upper part of the PLL-6 (0.3-3.20 m)  it is characterized by pronounced fluctuations in the values of carbon and nitrogen content:   the average carbon content is 0.09mol, the maximum value is 0.17 mol, the minimum is 0.07 mol, the average nitrogen content is very low, the average value is 0.02 mol, the maximum is 0.04 mol, the minimum is 0.02 mol, the value of the C/N ratio varies from 3.00 to 5.04, averaging 4.20.

The distribution of the obtained values of the carbon and nitrogen content is similar to the characteristic of PZHL-2. The average carbon content is 0.10mol, the maximum value is 0.19 mol, the minimum is 0.06 mol, the average nitrogen is 0.05 mol, the maximum is -0.12 mol, the minimum is -0.02 mol, the value of the C/N ratio varies from 1.05 to 5.04, averaging 2.21.

It is obvious that the increase in the C/N value in the upper part of PPL-6 is not associated with an increase in the carbon concentration, but with a decrease in the nitrogen content.

Fig. 7. Variations of carbon (1), nitrogen (2) and C/N ratio (3) in the PZHL-3 ice with depth

 PZHL-3 belongs entirely to the first tier of the upper edom complex of Batagai. According to radiocarbon dating of ice, this ice vein accumulated in the interval 30.8-27.1 cal. thousand years ago ^[5]. It is characterized by significant fluctuations in both carbon and nitrogen content.  The average carbon content is 0.17 mol, the maximum value is 0.36 mol, the minimum is 0.10 mol, the average nitrogen content is 0.03 mol, the maximum is 0.05 mol, the minimum is 0.02 mol, the value of the C/N ratio varies from 2.38 to 6.53, averaging 4.24.

Fig. 8. Frequency of occurrence of carbon (1), nitrogen (2) and C/N ratio (3) in samples of re-vein ice of the upper edom complex.

The bulk of the studied samples of re-vein ice is characterized by a carbon content of 0.06-0.13 mol, nitrogen – 0.02-0.04 mol, the ratio is more often observed in the intervals of 1.05-2.15 and 4.35-5.45 (Fig. 8). The average carbon content in the re-vein ice of the Batagai Edoma is 0.13 mol, the maximum is 0.36 mol, the minimum carbon content is -0.06 mol, the average nitrogen content is 0.04 mol, the maximum is 0.12 mol, the minimum is 0.02 mol. For the entire data array of re-core ice, the value of C/N is on average 3.90, maximum -6.96, minimum 1.05. The carbon and nitrogen content in re-core ice varies within narrow limits, it can be assumed that microparticles of organic matter mainly synchronous with the time of ice accumulation fall into the ice.  This is very important to take into account when radiocarbon dating ice.

According to the study of tundra soils ^[6], it was found that C/N is an indicator of the availability of organic matter for plants. Although the key process of nitrogen transformation in tundra soils, which determines the productivity of plant and microbial communities, is the rate of mineralization of nitrogen-containing organic matter of the soil and plant residues, nitrogen can also be available to plants and microorganisms both in the form of mineral and organic compounds ^[7]. The molar ratio C/N primarily characterizes the availability of nitrogen in soils. As is known, the majority of humus horizons of soils are characterized by a value of C/N equal to 8-10 ^[8], which corresponds to a high and average nitrogen supply of humus. A very high ratio (18-20) is characteristic of nitrogen-poor coarse humus soil horizons. A low C/N value (2-3) is characteristic of very humus-poor horizons ^[8]. In soil microbial biomass C/N is 6 – 8, in humic substances of soils C /N is approximately equal to 12 – 14 and higher, for peat horizons the value of C/N is about 70 – 80. In the zone of permafrost development, the C/N indicator is used as an approximate indicator of the degree of degradation of organic matter or an estimate of the rate of mineralization of sediments, i.e. the higher the mineralization, the slower the sediments have moved into the permafrost state ^[9].  Strauss and co-authors ^[10], studying the edoma of the Duvan Yar, noted that the period of 50-30 thousand years ago was characterized by a carbon content of 2-4% and C/N values from 8 to 12, which in terms of indicators is close to the upper horizon of the light-earth studied by us. These signs, according to the authors, indicate interstadial conditions. Low carbon content (less than 1) C/N values equal to 6-8 are considered by the authors as signs of stadium conditions. High C/N values equal to 18-20 were obtained for Lena Delta sediments dating from the end of the allered ^[11]. Fluctuations in the values of carbon, nitrogen and C/N ratios are explained by the mosaic conditions of the Late Pleistocene and variations in moisture ^[11]. Most likely, the humidification conditions could indeed change periodically due to a combination of a number of factors. In the Alaska edom (Baldwin Peninsula), C/N values are in the range 4.4-35, averaging 22.1 ^[12]. In our case, in the context of the Batagai edom complex, such high values do not occur, the maximum value is 9.5. It is obvious that the low carbon content and, as a consequence, the low C/N value in the Batagai edom is not the result of intensive decomposition of organic matter, but rather a consequence of the low intake of organic matter into the sediments during the accumulation of edom.

Conclusions

The authors studied the soils in the vicinity of the Batagai mega-ravine, syngenetic re-vein ice and the sediments containing them.

The content of carbon and nitrogen, as well as their ratio in re-vein ice in Edom, was studied for the first time.

According to the carbon and nitrogen content, as well as their ratio in the re-core ice of the upper Batagai edom complex, it was found that for the entire data array of re-core ice, the value of C/N varies with an amplitude of about 6, on average it is 3.90, the maximum is 6.96, the minimum is 1.05.

In modern soils near the Batagai mega-ravine, the C/N ratio is maximum, only in the uppermost horizon of the light-earth (up to 11.67) of the illuvial ferruginous permafrost in the same horizon a maximum of 0.87 mol carbon content is noted, the maximum is observed near the sole of the active layer.

In radiocarbon dating of ice, it is important to assess the variability of the C/N ratio, as well as the carbon and nitrogen content, which will allow us to assess the degree of processing of the dated organic matter. Since the carbon and nitrogen content in the re-core ice varies within narrow limits, it can be assumed that microparticles of organic matter mainly synchronous with the time of ice accumulation get into the ice.