The Main Elements of the Field Ice-wedge Sampling Strategies for Isotope and Radiocarbon Analysis

IntroductionThe main purpose of the article is to create an optimal strategy for field testing of re-core ice for isotopic and radiocarbon analysis

The scientific significance of this task lies in the need for detailed isotopic characterization of new well-dated sections of the northern regions of the cryolithozone and very detailed testing for isotopic (? ¹⁸ O and ? ² H) analysis of new sections. The solution of this problem will allow us to obtain a complete isotopic and paleotemperature scenario for the Holocene and the late north of Western Siberia, northern and central Yakutia, Chukotka, and the Arctic islands.

As a result of the application of an improved sampling technique for re-vein ice, reliable ranges of isotopic composition values can be obtained, which, combined with the age reference of the obtained isotopic distributions, gives a complete picture of isotopic variations in ice veins during a certain period of its formation. The high degree of detail of isotope measurements and reproducibility of the results of mass spectrometric analysis, as well as the possibility of determining the ratio ? ¹⁸ O-? ² H, will allow obtaining the most reliable data for paleotemperature reconstructions for each studied vein. 

The innovativeness of the proposed technique consists in comparing isotope-oxygen and deuterium curves obtained from two parallel and quasi-synchronous re-vein ices exposed by a single outcrop in the strata of Edom and Holocene sediments. It is necessary to analyze their similarities and differences. This makes it possible to significantly clarify the solutions to two main problems arising in the study of Late Pleistocene edom strata – determining the age of re-vein ice and determining the accuracy of isotopic and paleotemperature interpretation of isotopic records.

An important task is to create a new data protocol for radiocarbon analysis of organic residues obtained by both the conventional method and the AMS method in poorly studied sections of Edom and Holocene sediments. The scientific significance of this task lies in the detailed radiocarbon dating of new sections for poorly studied regions of northern Siberia and validation of dating using the latest Intcal20 calibration system, the scale of this task can be realized in a wide regional coverage of poorly studied territories and detailed testing and AMS radiocarbon dating of microinclusions of organic matter directly from ice veins and radiocarbon dating of new sections. The novelty of this task is determined by the possibility to carry out detailed reconstructions of the paleoclimate and date sudden and abrupt climatic shifts that occurred during the winter season in relatively short time intervals, which cannot be determined by other methods, and is also unlikely for regions where there are no re-vein ice.

The solution to this problem will be to create a pool of isotopic data: the average values of ?18 ^O in the most important time intervals of the formation of reference sections of the Late Pleistocene and Holocene for key regions of the cryolithozone of Russia (north of Western Siberia, Taimyr, north Yakutia, central Yakutia, Chukotka, Transbaikalia, etc.) and the construction of maps of isoscape values of ?18 ^O, for the most important time intervals of the Late Pleistocene and Holocene.

Previous experience in field testing of re-core ice for isotope and radiocarbon analysisField studies of re-vein ice in the northernmost regions of the Russian cryolithozone have been conducted by the author since 1976. In 1979, isotopic and radiocarbon studies of the Seyakhin edom strata on the eastern coast of Yamal were initiated, in 1983-2022, detailed isotope diagrams of polygonal vein complexes of more than 50 reference sections from Vorkuta to Uelen were obtained,^[2,5] providing the possibility of direct chronological comparison of isotopic records of underground and terrestrial ice and their reliable age reference for a period of more than 40 thousand years.

In 1998, for the first time in the world (in 1998), direct dating of re-vein ice was performed using accelerator mass spectrometry by radiocarbon analysis of microinclusions of organic matter in the re-vein ice of the Seyakhinskaya Edoma ^[8,12], and then in Holocene veins in the Shchuchinskaya thick in Yamal, the Bison, Plakhinsky Yar, and Zeleny Cape edom sections, Duvanny Yar,^[3-9] Anadyr in Chukotka Mammoth Mountain and Batagai^[13] in central Yakutia. 

    The method of sampling of re-vein ice in 1976-1978 was used by the author for palynological and hydrochemical analysis, and since 1979 for isotopic determinations. During the boat route along the Tanama River, a multi-tiered ice vein with a fully preserved primary structure in the form of seven veins nested into each other was encountered in the upper reaches of the river in the floodplain thickness (Fig. 1), each of which consisted of 10-50 elementary annual veins, but the elementary veins were not preserved as well as the veins formed by them. 7 tiers.

The vein of each subsequent tier wedged the previous one and at the same time all the individual contacts of the veins of all 7 tiers were preserved. Such a structure of this Holocene vein predetermined the approach to the most complete selection of ice of various compositions. As can be seen, with vertical selection, the transect intersects the veins of all 7 tiers, whereas with horizontal selection, the lower and upper transects intersect the veins of only three tiers. Thus, when selecting this vein for hydrochemical determinations, we found it necessary to perform a detailed selection by vertical transect and by two horizontal ones, although when studying Holocene veins, it is tempting to limit ourselves to horizontal selection only. But this vivid example shows that if only horizontal selection is made, this, as a rule, reduces the representativeness of the information received.   

Fig. 1. A late Holocene multi-tiered ice vein with a fully preserved primary structure in the form of seven nested veins in the upper reaches of the Tanama River, in the floodplain. The sketch was made by the author in the field and reproduced without changes.

Later, starting in 1979, the author was lucky enough to work on many edom sections of Western Siberia, Yakutia, Chukotka, and the Arctic islands. This required the development of a unified method of sampling from veins in edom strata for hydrochemical, palynological and isotopic determinations.^[2] In the most general form, the unified technique developed by the author and applied to all the studied sections of the edom strata is schematically shown in Fig. 2. According to this method, the selection was carried out vertically from the largest veins in the section and supplemented with several horizontal transects from the same vein, samples were taken in detail from buried small veins and from the texture-forming ice of the host edom deposits. These selections from the ice were necessarily accompanied by the selection of a variety of organic material from the syngenetic edom deposits containing the veins (see Fig. 2).   

Fig. 2. Schematic diagram of sampling in re-core ice. From Y.K.Vasilchuk, V.M. Kotlyakov ^{[4, p. 357]}. Ice: 1 – a powerful transit syngenetic vein; 2 – buried small veins; 3 – ice schliers; 4 – organic matter in the thickness: a – peat and scattered detritus, b – wood, c – bones; 5 – sandy loam; 6 – sampling for radiocarbon and isotope analysis: a – organics on radiocarbon analysis, b – texture–forming ice of schliers for isotopic analysis, c - vein ice for isotopic analysis

This technique is fully implemented, for example, when studying the section of the Blown Yar (Fig. 3), where isotope analysis is performed both on vertical and horizontal transects. This isotopic analysis was accompanied by dating of organic material of different composition from the host sediments, which made it possible to significantly refine the paleogeography of the Duvannoyarsky massif. 

Fig. 3. Structure of the lower part of the section of syncreogenic late Pleistocene deposits of the Duvan Yar and isotope-oxygen diagrams of re-vein ice according to samples selected: A – vertically, B – horizontally: 1 – large (transit) syngenetic re-vein ice; 2 – small (buried) syngenetic re-vein ice; 3 – segregational schlier ice; 4 – organic matter in sandy loam: a – peat and roots, b – bones; 5 – sandy loam; 6 – sampling for isotopic oxygen analysis: a - ice of large (transit) veins, b – ice of segregational schliers, c – ice of small (buried) veins. From Y.K.Vasilchuk, V.M. Kotlyakov ^{[4, p. 390]}Since 1998, when the author was able to directly date syngenetic re-vein ice in the edom strata, first in the Seyakhinsky section ^[8], and then in the Duvannoyarsky, Zelenomyssky, Plakhinsky on the Kolyma River, Mammoth Mountain on the Aldan River ^[9], the Phoenix section in the middle mountains of the Magadan region.

It was especially possible to date the Bison section in the lower reaches of the Kolyma, where samples were taken to date microinclusions of organic matter, humic extracts and spore-pollen concentrate (Fig. 4). An important feature of the study of the Bison section was a very detailed sampling for isotope-oxygen and deuterium determinations. Of the three up to 7-9 m high, more than 150 samples were selected and analyzed, which made possible very detailed isotope diagrams for the period from 26 to 33 thousand years.

Fig. 4. Sampling scheme of re-vein ice in the Bison section, lower reaches of the river.Kolyma: 1 – ice vein, 2 – sampling point for isotope-oxygen and deuterium analysis, black numbers – sample numbers, 3 – sampling point for analysis ¹⁴ With the AMS method

The main elements of field testing of re-core ice for isotopic and radiocarbon analysisAs a result of the application of an improved sampling technique for re-vein ice, the author assumes to obtain reliable ranges of isotopic composition values, which, combined with a confident age reference of the obtained isotopic distributions, will give a complete picture of isotopic variations in ice veins during a certain period of its formation.

The high degree of detail of isotope measurements and reproducibility of the results of mass spectrometric analysis, as well as the possibility of determining the ratio ? ¹⁸ O-? ² H, will allow obtaining the most reliable data for paleotemperature reconstructions for each studied vein.

To date, the most innovative task of isotope and radiocarbon analysis of re-vein ice is the comparison of isotope-oxygen and deuterium curves obtained from two adjacent, parallel and quasi-synchronous re-vein ice (Fig. 5), revealed by a single outcrop in the edom (Fig. 6) and Holocene sections of the northern regions of the cryolithozone.

Fig. 5. Parallel simultaneous sampling of re-vein ice from two adjacent ice veins of the Batagai edom strata

Fig. 6. Sampling scheme from the re-vein ice of the Batagai edom strata, performed in 2019: for isotopic analysis: red dots – from veins, yellow triangles – from textural ice; for radiocarbon – yellow squares

    Previously, this was not done in world practice. The idea of this task arose from the author in connection with the previously practically not discussed question of the degree of objectivity of the isotope record obtained from an arbitrarily selected ice vein. As a rule, this choice is made based on the completeness of the opening of the re-vein ice and the frontal exposure in relation to the direction of occurrence of the vein. By default, it was assumed that the selection made from other veins exposed by exposure would give the same results. Our preliminary studies indicate that this is not always done. At the same depths, both identical and markedly different isotopic definitions were obtained from samples from neighboring veins. The introduction of parallel sampling from two veins into the practice of testing key edom sections will significantly improve the accuracy and reliability of isotope recording.

Sampling for isotope analysis. The possibility of very detailed sampling from neighboring veins to obtain high-precision isotope determinations is associated with a relatively new field sampling technique tested using electric drills Makita DDF481rte 18B and Bosch GSR 36 VE-2-LI with steel ice crowns with a diameter of 51 mm with titanium nozzles. Samples are taken at a distance of no more than 0.2-0.3 m along both the vertical and horizontal axes of the exposed vein. This makes it possible to take more than 100 samples vertically from a 10 m high vein, which ensures detailed selection in increments of about 100 years. In addition, sampling using electric drills allows for very detailed horizontal sampling, which is also necessary to confirm the completeness of the isotope record. For each of the tested cores, a selection is made in at least 3 horizontal profiles for every 10 m of the height of the core. Performing vertical and horizontal testing of re-vein ice (Fig. 7) allows comparing spatial isotopic variations within different vein ice.

Fig. 7. Scheme of sampling from the re-vein ice of the Vilyui edom strata, performed in 2021: 1 – for isotope analysis; 2 – for radiocarbon analysis. From ^[14]

According to the method adopted by the authors for cleaning the sampling site, the near-surface 5 cm of ice was removed using a drill and then deeper samples were taken from the same hole (Fig. 8). The drill bit is cleaned before selecting each new sample.  An ice sample with a height of 4-6 cm (Fig. 9) and a diameter of 5 cm (Fig. 10) is drilled out of the veins.

Fig. 8. Sampling of re-core ice using an electric drill

Fig. 9. Height of a sample of re-core ice drilled with an electric drill

Fig. 10. Diameter of a sample of re-core ice drilled with an electric drill

The sample volume is about 20-30 ^cm3, single elementary veins are counted in each sample. The number of single veins in each sample, as a rule, does not exceed 10-15 pieces (see Fig. 10). The mass of each sample is about 20-35 g. Ice sampling is accompanied by a detailed description of the color, transparency, ice structure, thickness of ice and ground veins, inclusions, shape and size of xenoliths, air bubbles. The ice sample was packed in plastic bags.  The coordinates of the section and individual veins are recorded using GPS. It is particularly important to determine the altitude of the samples - for this purpose, the authors use a portable laser rangefinder Leica DISTO 5910, which allows measuring the parameters of exposure at a distance of up to 300 m, the accuracy of measuring the height and distance of which is ± 1.0 mm.

    Ice melts in bags at a temperature of +5 to +20 ° C. pH and EC meters were used to measure the acidity and electrical conductivity of water from melted ice. The measurement accuracy of the HANNA pHep 4 HI98127 pH meter is as follows: the pH range is from 0.0–14.0; the measurement accuracy is up to 0.1 pH units, the measurement accuracy of the HANNA HI 98311 EC meter is up to 0.1 µS/cm. Meltwater is poured into plastic bottles with a capacity of 10 ml with a tightly closed lid. The bottles are made of high-quality plastic.

     Sampling for radiocarbon analysis. Creation of a new data protocol for radiocarbon analysis of organic residues obtained by both the conventional (scintillation) method and the AMS method in poorly studied sections. Radiocarbon analysis of organic residues in newly investigated Edom and Holocene sections is performed both in deposits containing syngenetic veins, and directly on organic micro-findings from ice veins in which radiocarbon analysis is performed using AMS^[8,9]. The scientific significance of this task lies in the detailed radiocarbon dating of new sections and validation of dating using the latest Intcal20 calibration system, the scale of this task will be realized in a wide regional coverage of poorly studied territories and detailed testing and AMS radiocarbon dating of microinclusions of organic matter directly from ice veins and radiocarbon dating of new sections. The novelty of this task is determined by the possibility to carry out detailed reconstructions of the paleoclimate and date sudden and abrupt climatic shifts that occurred during the winter season in relatively short time intervals, which cannot be determined by other methods and for regions where there are no re-vein ice.

The author has developed a proven technique for sampling micro- and macro-inclusions of organic material from re-vein ice and from the deposits containing them for conventional (scintillation) ^[6,7] and for AMS ^[8,9] radiocarbon determinations. The previously developed strategy for interpreting radiocarbon data ^[11] allows us to select valid radiocarbon dating from arrays even with a significant admixture of allochthonous organic material and, as a consequence, with significant inversions of radiocarbon dating.

Here I would like to discuss one non-obvious point: in recent years, the works of our colleagues have shown a tendency to preferentially horizontal sampling of samples from vein ice in edom deposits ^{[15, p.4537]} and this trend increases If such priority selection can be considered as possible for Holocene veins (but it is shown above that it is better to supplement it with vertical selection), then for late Pleistocene veins, an insurmountable contradiction arises with exclusively horizontal selection. Let's imagine a situation that usually occurs with AMS ¹⁴ With the dating of microinclusions in Pleistocene syngenetic veins, when among the dating fields, for example, from 30 to 35 thousand years, there are one or two older dates. If this happens during vertical sampling, then we can, based on the revealed trend of the distribution of dates in syncryogenic strata (younger ice in syncryogenic veins of edom strata, as a rule, is located above the older one), for example, from 35 at the bottom to 30 thousand years at the top, exclude the older dating among them as clearly redeposed.^[11] If this is fixed with horizontal selection, then there are no grounds for excluding the older dating as inversion, because the vein could have been formed initially in this older period, and then resume its growth. As you know, the direction of growth in the width of ice veins can be quite arbitrary. Although, most often, ice growth occurs in the central axial part of the veins, and ice is usually older to the lateral periphery of the vein, but sometimes the zone of predominant cracking and accumulation of younger ice can shift to the marginal parts of the veins and in these cases younger ice is noted in the peripheral part of the veins. This is particularly observed in the veins of the Bison section, where older ice is found in the central part of the veins (see Fig. 4) Therefore, the transition to preferential horizontal sampling from vein ice in edom deposits should still be attributed to insufficiently thought-out actions and, undoubtedly, it should always be supplemented by vertical sampling from edom re-vein ice.

The described selection method for isotopic and radiocarbon determinations can be successfully used to obtain a more complete and reliable isotopic characterization of Edom and Holocene re-vein ice. It has already been implemented in recent studies carried out by the author on the Seyakhinsky and Batagaysky edom sections ^[12,13]. And such a complete and verified isotopic and geochronological characteristic is an important criterion for studying the spatial and temporal variability of winter climatic conditions.^[2,5,10] An important element of this study is the construction of isoscape maps (i.e. lines of equal isotopic values) for the key stages of the Late Pleistocene and Holocene (Fig. 11) of individual geocryological regions and the cryolithozone of Russia as a whole.   

Fig. 11. Isoscapes of ?18 ^O values for re-vein ice in the north of Western Siberia: A – for modern vein sprouts, B – for veins dated to the end of the North Grippian – Meghalayan Holocene periods (5.2–0.9 thousand cal. years ago), In – according to veins dated Greenlandic – the first half of the North Grippian period of the Holocene (11.4–5.3 thousand cal. years ago), G – by veins dated to the Greenland Holocene period (11.7–8.2 thousand cal. years ago). From N.Budantsev, Yu.Vasilchuk^[1]

ConclusionsThe main provisions of the optimal strategy for field testing of re-core ice for isotope and radiocarbon analysis are formulated:

1. The innovativeness of the proposed technique consists in comparing isotope-oxygen and deuterium curves obtained from two parallel and quasi-synchronous re-vein ices exposed by a single outcrop in the strata of Edom and Holocene sediments. A detailed analysis of the similarities and differences of isotope-oxygen and deuterium curves obtained from two parallel re-vein ice is proposed. This will significantly clarify the solution of two main problems arising in the study of Late Pleistocene edom strata – determining the age of re-vein ice and determining the accuracy of isotopic and paleotemperature interpretation of isotopic records. Previously, the comparison of isotope-oxygen and deuterium curves obtained from two parallel and quasi-synchronous re-vein ice, which is opened by a single outcrop, was not performed by anyone in the world.

2. Previously, it was believed that sampling of vein ice produced from different veins opened by the same outcrop would give the same results. Preliminary studies carried out by the author indicate that this is not always done. At the same depths, both identical and markedly different isotopic definitions were obtained from samples from neighboring veins taken in parallel and simultaneously.

3. Predominantly horizontal sampling from vein ice in edom deposits should still be considered an insufficiently justified procedure, horizontal sampling should undoubtedly be supplemented by vertical sampling from edom re-vein ice. Only with vertical selection it is possible to develop criteria for excluding older dating on allochthonous material as inversion, with horizontal selection it is still practically impossible.