A baseline survey of the geochemical characteristics of the Arctic soils of Alexandra Land within the Franz Josef Land archipelago (Russia)

The compositions of soils and their parent materials were studied within one of the most northern land areas of the world — the island of Alexandra Land of the Franz Josef Land archipelago. Contents of 65 trace and major elements were determined using atomic emission spectrometry (ICP-AES) and inductively coupled plasma spectrometry (ICP-MS). Other analyzed characteristics included soil pH, particle-size distribution and contents of carbon and nitrogen. The bedrock had an alkaline pH, whereas the soil pH ranged from weakly acid to alkaline. The textural class of the soils predominantly corresponded to sandy loam. The contents of clay and silt increased with depth due to the migration of these fractions with groundwater. The studied soils were formed on basalts with high contents of MgO, Fe2O3, TiO2, Cu, Co, V, Ni, Cr, Zn, and low contents of Pb and Hg. The present study confirms that the FJL basalts are similar to the Siberian Platform basalts in composition and belong to the continental basalt series. The composition of soils was generally similar to that of the bedrock. Compared to other Arctic archipelagos (i.e., Svalbard, Severnaya Zemlya), the soils of Alexandra Land are characterized by increased contents of Cu, Mn, Co, and Fe and reduced contents of Hg, Pb, and Cd. The median concentrations (mg kg−1) of trace elements in the soils were as follows: Cu—142, Zn—100, Ni—72, Pb—2.4, Cd—0.1, and Hg—0.0052. The low contents of Hg, Pb, and Cd in the soils are indicative of low inputs of these elements from both long-range transport and local sources of pollutants.


Introduction
The polar regions have become one of the areas where climate change and human impacts are most pronounced (Wang et al. 2022). The direct human impact on the landscape of the Arctic is limited, but remote human activity may change the chemical composition of the elements of the polar environment, especially by introducing contaminants such as heavy metals (Kozak et al. 2016). The Arctic is closely connected to the rest of the world, receiving contaminants from sources far outside the Arctic region (AMAP 2005). Such long-range transport of air pollutants from the industrial regions of Europe, Asia and North America has been described in many studies (Barrie et al. 1992;Akeredolu et al. 1994;Headley 1996;AMAP 1998;2005;Wojtun et al. 2013;Kozak et al. 2013;Ma et al. 2020).
The composition of Arctic soils is also affected by local sources of pollution (Gulińska et al. 2003;Wojtun et al. 2019). Local pollution in the Arctic region is caused by the development of mineral resources together with the impact of settlements and power industry facilities. Many studies have shown that Arctic soils are to different extents subjected to anthropogenic contamination (Bazzano et al. 2016;Krajcarová et al. 2016;Halbach et al. 2017;Zaborska et al. 2017;Wojtun et al. 2019;Łokas et al. 2019). The majority of such studies have been conducted on the island of Spitsbergen, focusing on the of baseline concentrations of heavy metals in soils (Plichta et al. 1991;Hao et al. 2013;Kryauchyunas et al. 2014;Szymański et al. 2019;Aslam et al. 2019), assessments of the impacts of different pollution sources on soils (Gulińska et al. 2003) and estimations of the deposition rates of airborne heavy metals (Wojtun et al. 2013;Kozak et al. 2013Kozak et al. , 2016. The importance of research on soil composition within polar regions is also associated with the current problems of global warming, which has the strongest impact on the Arctic (Gutiérrez et al. 2021). The thawing and degradation of permafrost triggered by global warming are regarded as one of the most important drivers of soil evolution processes within the polar regions of Russia (Kaverin et al. 2014). The consequences of global warming include an increased rate of seasonal ground thawing, which induces significant changes in the biochemical processes within soils (Vonk et al. 2019;Pokrovsky et al. 2020). Thawing permafrost could result in the release of organic and inorganic forms of nutrients and heavy metals (Pogojeva et al. 2021). Therefore, data on the contents and migration processes of chemical elements within such high-latitude soils are needed for making forecasts of changes in the Arctic ecosystems, which are the most vulnerable under the conditions of a changing climate (Usacheva et al. 2016). Increasing anthropogenic pressures, which result from either intentional or unintentional changes of terrestrial, freshwater or marine ecosystems as well as the forecasted climate change will probably lead to a significant and mostly irreversible loss of biodiversity in the Arctic (Hudson et al. 2017).
The sustainable development of the Arctic with its rich natural resources is currently one of the most important areas of the domestic policy of Russia (Serova and Serova 2021). Russia is the important player in the Arctic shelf with significant economic, security, and political interests in the region (Carayannis et al. 2017). The industrial development of the Russian Arctic increases the risks of ecosystem degradation. One of the strongest impacts on the high-latitude Arctic ecosystems is the influx of various chemical elements and compounds onto the surface of the soil following the emissions of these elements from gas industry facilities (Bashkin 2017). The deposition of trace elements from the atmosphere also makes a significant contribution to the pollution of Russia's polar regions. Previous studies in the Russian Arctic revealed a high level of heavy metal contamination of soils, snow and surface waters within the Kola Peninsula (Boyd et al. 2009;Dauvalter 2003), Norilsk industrial region (Zhulidov et al. 2011), Yamal peninsula (Ji et al. 2019), andNorthwest Siberia (Pozhitkov et al. 2020). The problem of heavy metal contamination has raised interest in studying the contents of trace elements in soils of Arctic Ocean islands, in particular, the Novaya Zemlya archipelago (Laverov et al. 2016;Usacheva et al. 2016) and Belyi Island (Abakumov et al. 2017;Moskovchenko et al. 2017).
Taking into account the increasing anthropogenic impact on the Arctic region, it is necessary to determine the background contents of chemical elements in the soils. Such research provides the scientific basis for an objective and accurate assessment of the impact of human activities on the natural environment (Lu et al. 2012).
The present study on the composition of soils and their parent materials (bedrock) was conducted within Alexandra Land, which is one of the largest islands of the Franz Josef Land (FJL) archipelago. It is one of the most northern land areas, being located at a distance of approximately 1000 km from the North Pole. Although the number of studies in the Arctic has generally increased over the last decade, the soils of the FJL are still new materials for specialist research for almost every aspect of soil science and ecology (Nikitin et al. 2020). Specifically, there are hydrocarbon deposits on the shelf adjacent to FJL (Soloviev et al. 2015), and therefore, the future development of the region will benefit from baseline monitoring of the soil composition.
The specific aims of this study were (1) to analyze the chemical composition of the soils and parent materials within Alexandra Land to determine the baseline concentrations of elements and (2) to identify the effects of soil particle-size composition, acidity/alkalinity levels and organic matter contents on the concentrations of trace and major elements.
Alexandra Land has a total area of about 1300 km 2 . The island's highest altitude of about 390 m a.s.l. is found on an ice cap in the southern part of the island, whereas the land free from ice has a maximal height of only 70 m a.s.l. The FJL archipelago is located within the zone of Arctic climate, where soils are formed under conditions of extremely low temperatures (the mean annual T from − 6° to − 10 °C and the mean T of July from + 0.2 to + 1.1 °C). Over a half of the island's total area is covered with ice. The ice-free areas have a continuous permafrost with the active layer depth between 15 and 50 cm and a ground temperature between − 7 and − 13 °C (Kondrat'eva 1980). According to the data from the local weather station, which is located on Hayes Island (80 o 37' N, 58 o 02' E), the current warming of the Arctic severely affects the FJL archipelago due to the increase in the mean annual temperature by more than 5 °C over the period of 1958-2018 (Fig. 2). The mean annual precipitation is about 300 mm. The vegetation cover is sparse due to the low temperatures and mainly consists of moss-lichen-grass communities of the High Arctic tundra, where mosses and lichens predominate over vascular plants (Safronova et al. 2020).
The topography of the FJL archipelago is dominated by residual landforms of the basalt plateau. There are only very small areas of erosional-denudational and depositional coastal landforms composed of loose sediments that occur in the eastern and some central islands (Sukhodrovskii 1970). The surface of Alexandra Land mainly corresponds to gently sloping terrains covered by rock debris and weathering products of bedrock. The landforms of Alexandra Land also include glaciers, blockfields and bedrock outcrops, narrow floodplains, coastal lowlands and sandy beaches.
The geology of the FJL archipelago has been previously studied (Ntaflos and Richter 2003;Soloviev et al. 2015). The archipelago is mostly composed of sedimentary and volcanic rocks. The upper geological strata of Alexandra Land consist of basalts and dolerites (Karyakin and Shepilov 2009). Basalts of FJL were formed between 197 − 121 Ma, i.e., from the Early Jurassic to the Early Cretaceous (Simonov et al. 2019). The rocks are Fig. 1 Location of the study area, the soil sampling sites (S1-S12) and the bedrock core (B1) geologically classified as continental tholeiites (Ntaflos and Richter 2003).
Despite its remote location, FJL is affected by the longrange transport of air pollutants. The most significant sources of such airborne pollutants are located on the Kola Peninsula, in Northern Europe and the Norilsk region (Vinogradova and Ponomareva 2012).

Soil sampling and analyses
The soils and bedrock of Alexandra Land were sampled during the UMKA-2021 complex Arctic expedition, which was organized by the Russian Geographic Society. The sampling strategy was defined after the analysis of the predominant landforms during the preliminary fieldwork across the island. This approach was adopted to allow the assessments of the most typical landforms within the time limitations in the field due to logistic constraints. A total of 13 sites were selected representing three predominant types of landforms: gently sloping watersheds, peri-glacial areas and coastal lowlands (Fig. 1). The studied soils within watersheds were identified as follows: Skeletic Cryosol (Loamic, Humic) (S1, S4, S5, S6, S9), Turbic Cryosol (S3), and Turbic Cryosol (Arenic) (S10, S13). Oxyaquic Cryosols (Humic) (S7, S8) were examined in the coastal lowlands. The profiles S11 and S12 were collected from the peri-glacial zones of the Lunnyi and Kropotkin glaciers, respectively. The soils here were classified as Leptosols (Loamic). All locations were recorded using GPS.
All soil samples were taken by cutting pits of approximately 30 × 30 × 30 cm using a steel shovel. Soil pits were vertically sampled from three layers (0-10, 10-20 and 20-30 cm depths). Sampling in layers provides determination of the subsurface translocation of elements as a function of the quantity of organic matter, pH, etc. A similar technique was used to assess the composition of soils in Svalbard (Krajcarová et al. 2016;Halbach et al. 2017). In our study, the exception was the soils of peri-glacial zones where only the surface 0-10 cm layers were sampled.
The composition of bedrock was investigated by coring to the depth of 5 m in a single location, with a total of seven core samples taken from the following depths: 0.4, 0.8, 1.4, 2.0, 3.2, 4.0 and 5.0 m.
In the laboratory, plant root fragments were removed and soil samples were air-dried at 25 °C to constant weight. The samples were subsequently crushed using a laboratory ball mill KM-1 (Russia). The pH values were measured potentiometrically in continuously mixed 1:2.5 soil:water and soil:KCl suspensions using a Starter 3100 conductivity meter (OHAUS, Germany). Total carbon (TC) and total bound nitrogen (TNb) measurements were taken using a vario TOC (Elementar) device. The particle-size composition of the 0-2 mm fraction was determined by a Mastersizer 3000 (Malvern) laser diffraction particle-size analyzer using water and ultrasonic sample dispersion. Thin sections were prepared from six bedrock samples and investigated under a polarizing microscope (MP-3, Russia) at the Tyumen Industrial University.
The chemical composition of soil and bedrock samples was investigated by the methods of inductive coupled plasma mass spectrometry (ICP-MS) and inductive coupled plasma atom emission spectrometry (ICP-AES). For analysis, portions of samples weighing 100 mg were used. Digestion of samples was performed in an open beaker system using a certified procedure (with a combination of three acids HClO 4 , HF, and HNO 3 ). The contents of the macrocomponents (Na, Mg, Al, P K, Ca, Ti, Fe in weight percent oxide and S total ) and some trace elements (Li, V, Cr, Mn, Co, Ni, Cu, Zn, Sr, Ba) in the samples were determined using a Scientific iCAP-6500 Duo ICP-AES (USA). A Thermo Scientific X-7 ICP-MS (USA) was used only for the analysis of trace elements (Li, Be, Sc, Cr, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Nb, Mo, Rh, Ag, Pd, Cd, Sn, Sb, Te, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Ir, Pt, Au, Tl, Pb, Bi, Th, and U). The combined use of ICP-MS and ICP-AES for some elements allowed for the testing of the validity of measurements by comparing the measurements of 7-9 elements obtained by both methods simultaneously. The methods of analysis have been described in detail earlier (Karandashev et al 2008;Fedotov et al. 2016;Ermolin et al. 2018). Along with the analyzed samples, the decomposition and the analysis of certified reference materials were carried out. To check the accuracy of measurements, we used multi-element certi- Survey). The comparison with the certified reference materials showed a sufficient repeatability (85-115%) for the majority of the analyzed elements, except for Sn (59%), Ba (70%), Ag (153%), W (63%), the measurements of which were excluded from the analysis. The detection limits were defined as three times the standard deviation of replicate blank measurements. The methods, detection limit (DL), recoveries and analytical results of certified reference materials are given in the Supplementary Materials (SM Table 1).
Since the content of Hg was below the detection limit in about half of the samples analyzed, the method of atomic absorption spectrophotometry was additionally applied to specify the contents of this element. To analyze the Hg content, samples weighing from 20 to 100 mg were used. The samples were placed in a dispenser spoon, injected into a prefix heated to 700 °C, where the catalytic degradation of the compounds of the soil sample matrix and the release of mercury took place. Mercury vapor entered the analytical cell of the analyzer and was detected. The analytical signal was processed using RAPID software. All soil samples were analyzed in two replications by atomic absorption spectrometry with RA-915 M and pyrolytic prefix RP-91S (Lumex, Russia). The calibration coefficient was determined on the basis of a standard soil sample of sod-podzolic sandy loam (SDPS-3). Stability control of the calibration coefficient was carried out before starting work. The comparison of the results of ICP-MS and AAS showed a sufficient repeatability. The results of detection of mercury by two methods are given in the Supplementary materials (SM Table 2).
Statistical data processing was performed using Statistica 10.0 software. Mean (M) and median (Me) values, standard deviation (SD), and skewness coefficients (SC) of major and trace elements, pH, TC and TN were calculated. Some of the measured data fell below the detection limit. In this case, half of the detection limit was applied (Helsel 1990).
Normality tests were used to evaluate data distribution (Kolmogorov-Smirnov). Median values were used due to the absence of normal distribution in the concentrations of many elements (K 2 O, S, As, Rb, Mo, Cd, Cs, Ba, Tl, Bi, U as well as TC). The median absolute deviation (MAD) was used as a measure of variability as follows: MAD = median (| xi-median(x)|) (Falk 1997). where x represents the analyte. Spearman rank coefficients were calculated (with the probability value P < 0.05) in order to analyze relationships between the element contents, pH values, particle-size distribution and the contents of TC and TN. Differences between soil horizons and parent rocks were evaluated with the Mann-Whitney test. A comparison with the Earth continental crust average (ECA) (Rudnick and Gao 2003) and world soils average (SWA) (Kabata-Pendias 2010) was conducted to assess general geochemical characteristics of the rocks and soils.

Bedrock composition
In this study, the mineralogical analysis of thin sections of bedrock showed that it was formed of basalt with porphyritic texture, consisting mainly of plagioclase crystals and small grains of augite, which were immersed into a yellowish brown altered obsidian (palagonite). Inclusions of carbonates and ore minerals were observed at the 4.0 m depth. According to the previous petrographic study (Simonov et al. 2019), the archipelago's volcanic rocks are generally homogeneous in composition and usually consist of basalts with 5-20% obsidian and small inclusions of predominantly plagioclase and clinopyroxene (augite) and occasionally olivine. Therefore, the studied samples of bedrock were typical for the FJL in terms of mineralogy.
The element composition of bedrock was characterized by relatively high contents of Fe 2 O 3 and Al 2 O 3 , i.e., 15 and 14%, respectively (Table 1). Other elements were less abundant, with their contents decreasing in the following order: CaO, MgO, NaO, TiO 2 , K 2 O, P 2 O 5 and MnO. The studied basalts, especially in the upper part of the core, were very poor in K 2 O, the content of which ranged between 0.33 and 0.38%, which is 7-8 times as low as the value of its world crust average (ECA). It should be noted that the high Fe 2 O 3 content in the studied core was 3 times higher than the ECA. The observed TiO 2 content of 2% on average is also above the ECA value.
The studied basalts were characterized by an abnormally high concentration of Cu, which was by an order of magnitude higher than the ECA for this element. The highest Cu concentration of 533 mg·kg −1 was observed at the depth of 5 m, whereas the other samples contained generally lower concentrations, within a narrow range of 206-266 mg·kg −1 . Concentrations of Co, V, Ni, Cr and Zn were also higher than their ECA values (see Table 1). The generalized data on the composition of different rocks of the world (Voitkevich et al.1990) show that mafic rocks, such as basalts and gabbro, tend to have increased concentrations of Fe, Ti, Cr, Ni, Co, Mn, Cu and Zn. Therefore, the composition of the studied rocks generally reflects the common geochemical features of basalts, except for the Cu concentrations being significantly above its average content of 100 mg·kg −1 in the Earth's mafic rocks. It is known that Cu concentrations in basalts are mainly related to sulfide concentrations (Krivolutskaya and Kedrovskaya 2020), which gives us the basis to suggest that the studied samples have high sulfide contents. This suggestion was confirmed by the presence of high concentrations of S total in the studied samples as compared to the composition of the precursor of volcanic rocks, i.e., primitive mantle, which has a mean sulfur content of 0.025% (McDonough and Sun 1995). The studied rocks had low contents of Pb, Th, U, La, Bi and Sb. The lanthanides (Ln) were subdivided into two groups -one with concentrations below ECA (La, Ce, Pr, Nd, Sm) and the other with concentrations above ECA values (Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). The Ln/ECA ratio increased with increasing atomic numbers of the lanthanides (see Table 1). It is known that the increase in the lanthanide atomic numbers in the periodic table is accompanied by a decrease in their ionic radii, which predetermine their distribution within the Earth's crust (Perelman and Kasimov 1999). Therefore, the observed growth of lanthanoid concentrations proportional to their atomic numbers can be explained by changes in their ionic radii.
We have shown that the studied rocks belong to the continental tholeiitic series (platobasalts) by analyzing the distribution and indicator ratios of accessory elements. For example, the studied basalts had Rb concentration of 9 mg·kg −1 , which is three times that found in oceanic basalts according to (Gale et al. 2013). Moreover, there was a highly significant difference in terms of the Rb/Cs ratio, which had values of 17.2 and 77.6 in the studied basalts and their oceanic counterparts, respectively. According to (Krivolutskaya and Kedrovskaya 2020), the continental basalts of the Siberian Platform have a Gd /Yb ratio of 1.3-2.0, with a mean of 1.56, which is very close to the data obtained in the present study on the Alexandra Land basalts (the Gd /Yb ratio of 1.4-1.7, with a mean of 1.6). Likewise, there are comparable values of the TiO 2 /Y ratios, with a mean of 644 in the Siberian Platform basalts and a mean of 661 (range of 562-711) in the FJL basalts. Therefore, the present study confirms that the FJL basalts are similar to the Siberian Platform basalts in composition and belong to the continental basalt series.

Soil composition
The total carbon content of the Arctic soils of FJL is known to be very sensitive to the impacts of climate change (Nikitin et al. 2020). For that reason, it was important to determine the current TC concentrations in the studied samples of soils and bedrock. The data obtained on the TC and TN contents as well as pH values are presented in Table 2.
As expected, the TC and TN values decreased with depth (see Table 2). The TC had a median value of 3.0% within the 0-10 cm layer, which decreased to less than 1% in the deeper layers of soils and bedrock. The TC contents broadly varied within each studied layer, e.g., from 0.7% in Arenic Cryosol (S10) to 17.6% in Humic Cryosol (S6) at the 0-10 cm depth. Such wide variability is known to be caused by the heterogeneity of vegetation cover. According to (Nikitin et al. 2020), the lowest TC values are associated with the sites where vegetation consisted of algae and lichen communities, and the highest TC values (up to 30.7%) are found at the sites with moss and grass communities. It should be noted that one of our sites (S3) had an inverse vertical distribution of TC and TN in the soil, with the maximum at the 20-30 cm depth and the minimum at the 0-10 cm depth. As it has been mentioned by (Nikitin et al. 2020), such a phenomenon is frequently observed in soils of FJL and can be explained by cryogenic processes (ground heaving and cryoturbation). The TNb content significantly varied within the studied soils with its maximum value reaching 0.44-0.59% observed in the upper Cryosol (Loamic, Humic) of S6 and S9. The TNb content expectedly decreased in the lower soil horizons. The highest TN contents with a median value of 0.16% were found in the upper 0-10 cm layer and decreased with depth to 0.07% within the 20-30 cm layer. The parent materials had even lower TN contents, i.e., less than 0.068%. There was a strong positive correlation (R = 0.86) between the TNb and TC contents.
As a rule, the highest TC:TN ratio was observed in the upper layers where plant residues accumulate. Nevertheless, this pattern is sometimes interrupted due to cryoturbation processes. The highest TC:TN ratio was observed in the lower (20-30 cm) Turbic Cryosol (S3). Still, other samples taken from lower mineral horizons demonstrated ratios from 5.1 to 13.3, which fits within the range of 3-16 suggested earlier by Nikitin et al. (2020), as typical for mineral horizons in the FJL archipelago.
There were spatial variations in TC:TNb ratio. Its lowest values ranging between 4.8 and 11.4 were observed in Skeltic Cryosol (Loamic) in the northern part of the island (S4 and S5), Oxyaquic Cryosol (Humic) (S8) and soils of peri-glacial zones (Leptosols (Loamic)), Sites S11 and S12), which was explained by their very weakly developed humus layer with low carbon contents. The highest TC:TN ratios of 34-36 were found in Skeletic Cryosol (Loamic), S6 and Turbic Cryosol, S3 in the southern part of the island. The increase in the TC:TNb ratio in the southern part of the island is associated with a more intense accumulation of plant residues.
The pH H2O of the studied soils was predominantly neutral, with a median value of 7.21, and a range of variations from weakly acid to alkaline, i.e., from 6.45 to 8.87. The pH KCl had a median of 5.74, with a variation range from 4.71 to 7.47. Soils with relatively higher organic matter contents had the lowest pH, i.e., there was a significant negative correlation (R = − 0.72) between the pH and TC values. However, the increase in pH with depth did not correlate with the decrease in TC, which could be explained by cryoturbation processes resulting in soil mixing. The Alexandra Land's soils with mostly neutral pH values can be contrasted to the soils of the Novaya Zemlya archipelago with the pH between strongly acid and acid (Usacheva et al. 2016). Apparently, rates of organic acid production are very low in the soils of the Alexandra Land due to the sparse vegetation cover. Despite the very slow development of soil acidification processes within the study area, the Mann-Whitney test showed that the observed values of soil pH significantly (p < 0.05) differed from the bedrock pH, with the latter being more alkaline (see Table 2).
The textural class of the studied soils predominantly corresponded to sandy loam, with the average proportions of sand, silt and clay being 58%, 37% and 3%, respectively. The contents of fine fractions (PM2, PM10, PM50) regularly increased with depth, e.g., the clay (< 0.002 mm) content increased from 2.4 to 2.7% and the silt (0.002-0.05 mm) content -from 35.8 to 42.6% (Table 3). The total content of sand fractions reached the maximum of 68.3% in the Turbic Cryosol (Arenic) of S10 (Fig. 3). The highest proportion of PM2 was observed in the soils of peri-glacial zones (S11 and S12), with the clay content of 5.9% and the silt content of 59.7% on average (see Fig. 3). The soils of peri-glacial zones are probably affected by deposition of fine particles from the glacier's meltwaters. A similar process of formation of clay deposits within glacial valleys has been described in Spitsbergen (Dobrovol'skii 1990). Table 3 The particle-size distribution at different depths in the studied soils (mean ± SD)
The ratios of the contents of elements in the studied soils to the soil world average contents of those elements show that the studied soils are enriched in MgO, CaO, TiO 2 , Fe 2 O 3 , Sc, V, Cr, Co, Ni, Cu and Zn, with the bedrock being enriched in the same elements (see Table 4). A majority of the analyzed elements had slightly lower concentrations in the soils as compared to the bedrock, with the soil/rock ratios being around 0.8-0.9 (Table 4). Such differences between the soils and the bedrock within Alexandra Land were generally less significant than soil-bedrock differences on the more southern islands of the Novaya Zemlya archipelago, where soils are relatively impoverished in Ti and Fe and enriched (by multiples of 2-5) in P, S, Cl, Cu, Pb and Zn (Laverov et al. 2016). In the Arctic, the bedrock composition is well reflected in that of soils due to the predominance of physical alteration of rocks with only insignificant contributions of chemical processes, as compared to the regions to the south of the Arctic (Dobrovol'skii 1990). The slight differences in the rock and soil composition are indicative of a weak soil-formation process within the FJL archipelago.
Most of the analyzed elements had similar contents in the 0-10, 10-20 and 20-30 cm soil layers and parent rocks, with the Mann-Whitney test showing only insignificant differences (p < 0.05). Likewise, upper and lower soil horizons in Spitsbergen insignificantly differ by the contents of elements, except for Cr (Krajcarová et al. 2003). The absence of statistically significant differences can be explained by (1) slow rates of soil-forming processes and low contents of organic substances in soils and (2) impacts of cryogenic processes, which cause mixing of soil materials.
However, the concentrations of some of the analyzed elements differed by 1.4-1.5 times between the upper, middle and the lower soil layers. As is shown in Fig. 4, the contents of K 2 O, Fe 2 O 3 , Co, Ni, Zn, Li, Cu and As in the 0-10 and 10-20 cm layers are significantly lower than those in the 20-30 cm layer. The contents of CaO, P 2 O 5 , Hg are only slightly (by 1.1-1.2 times) increased in the upper layer as compared with their contents in the lower layer.
According to the conclusions of the Arctic Monitoring and Assessment Program (AMAP 2005), assessments of heavy metals should focus on Hg, Pb and Cd, because these elements are potentially highly hazardous to the cells of living organisms in the Arctic. The Hg content varied significantly, from < 0.007 to 0.086 mg·kg −1 , with the higher concentrations being found in the Turbic Cryosol of S3. In the upper part of the Earth's crust, the average Hg content is 0.050 mg·kg −1 (Rudnick and Gao 2003). In the world soils, the average Hg content is 0.07 mg·kg −1 (Kabata-Pendias, 2010), which is significantly higher than the values we obtained. The data on low mercury contents in the soils of the Russian Arctic, up to 0.040 mg kg −1 (AMAP 2005), should be adjusted downward.
The present study showed that the content of Pb in the soils of the Alexandra Land was extremely low, with its mean value being by an order of magnitude lower than its SWA. Even the highest Pb content (12.6 mg·kg −1 ) detected by us in the peri-glacial soil was below the SWA value. The Cd content was also low, with its median being 4 times lower than its SWA.
The reasons for the low Hg, Cd and Pb content in the soils of the island merit discussion. The supply of heavy metals to soils depends on natural and anthropogenic sources. The low content of Hg and Pb in the soils can be explained, among others, by the extremely low content of these elements in the parent rocks. Pb and Hg content in the rocks was one order of magnitude lower than ECA. Hg concentration in all the studied samples was below the detection limit of ICP-MS method of analysis. The content of Pb was by an order of magnitude lower than the ECA for this element. Only the content of Cd was elevated in reference to its mean content in the Earth's crust. But it needs to be mentioned here, however, that Pb and Hg were enriched in soil as compared to the local bedrock, and it may be a signature of supply from the atmosphere, or bio-concentration.
The contents of Hg and Pb mostly depend on the amount of organic matter. Organic matter has a significant effect on the fixation of Pb in highly humic soils (Morin et al. 1999). In Canada, the content of Hg in soils decreases from south to north, which has been explained by a decrease in both ecosystem productivity and the rate of accumulation of organic matter (Olson et al. 2018).
Hg, Pb, and Cd can also originate from anthropogenic sources, both local and remote. Based on a modeling of deposition of heavy metals in the Arctic, the FJL archipelago has been classified as moderately polluted (AMAP 2005). A study of atmospheric deposition of trace elements from snowfall (Shevchenko et al. 2017) has demonstrated that Cd and Pb may originate from long-range transport from southern desert and steppe regions. Anthropogenic aerial deposition of Cd and Pb and their subsequent accumulation in the upper soil horizons has been identified by studies on the Yamal Peninsula situated approx. 800-1000 km south from the FJL archipelago (Ji et al. 2019). Monitoring of atmospheric depositions of Hg, however, showed mild contamination with this element (Eyrikh et al. 2022). Considering the low contents of Pb, Hg, and Cd in the soils of Table 4 Summary statistics of major (%) and trace element concentrations (mg·kg −1 ) in the soil samples from the Alexandra Land (n = 33) The SWA is the soil world average (Kabata-Pendias 2010) The concentrations of Se, Rh, Pd, Re, Te, Ir, Pt, Au and Bi are below their detection limits Hg content is based on ICP and AAS results. The highest soil/ rock ratios are shown in bold n number of samples, SD standard deviation, Me median value, MAD median absolute deviation, SC skewness coefficients the FJL archipelago, long-range transport of pollutants from industrially advanced regions has only a weak effect here. The distribution of chemical elements in the Arctic soils and sediments depends on the contents of clay and silt fractions, pH, organic matter content and the presence of anthropogenic pollutants. For example, the contents of Zn, Cu, Hg and Cr in soils of the Belyi Island (Kara Sea) have a significant positive correlation with the clay contents (Moskovchenko et al. 2017). The contents of Pb and Cu in the soils of Spitsbergen negatively correlate with the percentage of the 1-0.1 mm sand fraction (Melke 2006). The organic matter content has positive correlations with concentrations of Hg (Halbach et al. 2017), Pb and Zn (Melke 2006). An intensive leaching of Mn from acid Arctic soils results in the low concentrations of this element (Moskovchenko et al. 2017). Soil moisture distribution also affects the element contents, e.g., heavy metals tend to accumulate within waterlogged areas (Wojtun et al. 2013).
Factors that control the distribution of elements in the soils of the Alexandra Land were assessed on the basis of correlation analysis. The obtained values of correlation coefficients between the element contents and their distribution factors (clay content, soil pH and organic matter content) indicated that none of those factors was absolutely dominant. As a rule, values of R < 0.7 prevailed, i.e., strong correlations were absent (Table 5). The TC content positively correlated with concentrations of Hg, Pb and most lanthanoids and negatively correlated with Ni, Cr and Na concentrations in the studied soils. The observed relationship between Hg, Pb and TC confirms the dependence of those element concentrations on the organic matter content, which has been previously identified in the soils of Spitsbergen (Melke 2006;Halbach et al. 2017), Northwest Siberia (Opecunova et al. 2018 and Alaska (Olson et al. 2018), and accounts for the accumulation of those elements within the upper layer of soils of the Alexandra Land (see Fig. 3). The formation of compounds with organic matter is one of the main geochemical properties of mercury; plants are able to synthesize various metallo-complexes such as methyl-mercury (Kabata-Pendias 2010). The bioavailability of Pb had been interpreted in terms of the formation of stable organo-lead species (Manceau et al. 2002).
The soil pH positively correlated with Ni and Cr concentrations and negatively correlated with TiO 2 , V, Mo, Hg and most lanthanoid concentrations (Table 5). It is known that Ni and Cr are most mobile in acid medium and least mobile in alkaline medium (Kabata-Pendias 2010). The increased concentrations of Ni and Cr in soils with high pH were probably due to their weak leaching from alkaline and neutral soils.
The concentrations of lanthanoids were positively correlated with the TC content and negatively correlated with the pH. Lanthanoids have a low biological activity (Perelman Fig. 4 Chemical element contents in the soil layers: 1 -upper (0-10 cm), 2 -middle (10-20 cm), and 3 -lower (20-30 cm) and Kasimov 1999). Therefore, the observed positive correlation with TC is unrelated to the organic matter accumulation directly. However, the organic enrichment causes a decrease in the soil pH, and lanthanoids are not very mobile in a weakly acidic medium. Perelman and Kasimov (1999) mention that the alkaline groundwaters of the Kola Peninsula are enriched in rare-earth elements. It is highly probable that lanthanoids are actively leached from neutral and alkaline layers of the studied soils and rocks of Alexandra Land. This suggestion is confirmed by the fact that light lanthanoids with low atomic numbers, from La to Gd, are relatively more mobile than heavy lanthanoids, from Tb to Lu (Kabata-Pendias 2010). Lanthanoids of the light group correlate with the pH, whereas many elements of the heavy group (Ho, Er, Tm, Yb and Lu) don't show any statistically significant correlation. The soils that were relatively enriched in organic matter have relatively higher concentrations of lathanoids, Pb and Hg, but lower concentrations of Ni and Cr. It is known that Ni and Cr are very weakly concentrated by plants (Kabata-Pendias 2010), and they are mobile in acid medium (Perelman and Kasimov 1999). The latter results in their leaching from soils.
Correlations between the metal concentrations and the clay content in the studied soils were, contrary to our expectations, only weak in most elements (Al 2 O 3, K 2 O, Tl, Sc, Ba), although significant and always positive. Only Co and Cu had a strong correlation (R > 0.7) with the clay content (Table 5). Therefore, the above-mentioned increase in Co concentrations in the lower layers can be explained by the migration of elements in colloidal forms with groundwater, which is typical for soils of northern regions (Pokrovsky et al. 2006). Alexandra Land is located in a remote area of the Earth. It is composed of volcanic rocks, which distinguishes it from other Arctic islands, in particular Spitsbergen, which is predominately covered with sedimentary or meta-sedimentary rocks, both siliciclastic and carbonaceous, and the Novaya Zemlya archipelago dominated by shales, limestones, dolomites, silts, and sandstones (Laverov et al. 2016;Krupskaya et al. 2017). For that reason, it is interesting to compare our data with the results of other studies on islands of the Arctic Ocean, which are summarized in Table 6.
In Alexandra Land, the soils have a relatively low concentration of Hg due to its even lower concentration (below detection limit) in the parent materials. The low concentration of Hg in the studied soils is also due to the fact that the FJL archipelago is very far from the main industrial sources of Hg emissions. The Pb concentration within the study area has the lowest value ever reported for Arctic soils, which is explained by the composition of basalts and by the absence of contamination sources.
The Cd concentration in the soils of Alexandra Land was similar to that in some soils of Spitsbergen (Plichta et al. 1991;Wojtun et al. 2019), but significantly lower than that in the soils of Novaya Zemlya (Usacheva et al. 2016). Even the highest Cd concentrations (0.33-0.47 mg kg −1 ) detected at site S3 are below its maximal permissible concentration of 1.1 mg kg −1 , i.e., below the level that indicates the Cd pollution of soils (Kabata-Pendias 2010).
The Cu concentration within the study area is very high as compared to the other Arctic islands (i.e., Spitsbergen, Severnaya Zemlya Archipelago and Belyi Island). However, even higher Cu concentrations were found in some parts of Spitsbergen, e.g., the Cu concentration of 658.6 mg kg −1 in soil has been reported from the Pyramiden settlement area (Krajcarová et al. 2016). The soils of Alexandra Land also have relatively high concentrations of Fe, Mn and Co. The concentrations of Zn, Ni and Cr in the studied soils are at Ni ( In general, it should be noted that the elemental composition of soils of Alexandra Land is markedly different from the soil composition of other Arctic islands. The islands of the FJL archipelago are mainly composed of basalts with high concentrations of Cu, Fe, Mn, and Co and low concentration of Pb typical of them. Coastal sediments of the FJL archipelago significantly differ from other Arctic areas, too. Coastal sediments from FJL show significantly different clay mineral associations as compared to those from Novaya Zemlya islands, which is mainly due to different parent rocks (Nürnberg et al. 1995).

Conclusion
A baseline survey of the mineralogical composition, particle-size distribution, major and trace element composition and the chemical properties (pH, TC and TN) of soils and bedrock within Arctic ecosystems of Alexandra Land, belonging to the Franz Josef Land archipelago, was performed. It was found that the parent materials were basalts composed of plagioclase, augite and obsidian, with a very high concentration of Cu, which was by an order of magnitude higher that the world crust average content of this element. The concentrations of Mg, Fe, Ti, Co, V, Ni, Cr and Zn were relatively high, and the concentrations of Pb, Th, U, La, Bi and Sb were low. Based on the values of Gd/ Yb and TiO 2 /Y ratios, the studied rocks were similar to the continental trapp rocks of the Siberian Platform.
The studied bedrock had an alkaline pH. The soil pH ranged from weakly acid to alkaline, with the lowest pH values being associated with the highest carbon (TC) contents in the soils. The proportions of clay and silt fractions increased with depth. The highest proportions of fine fractions were found in the soils of peri-glacial zones.
The carbon (TC) contents had median values of 3% within the upper (0-10 cm) layers and less than 1% in the deeper layers of the studied soils. The nitrogen (TN) contents ranged from 0.01 to 0.59%, with the highest median value (0.16%) within the upper layers. However, soil mixing due to cryogenic processes occasionally resulted in an inverse vertical distribution of both TC and TN.
As compared to the soil world average values, the studied soils were enriched in MgO, CaO, TiO 2 , Fe 2 O 3 , Sc, Co, V, Cr, Ni, Cu and Zn. The results obtained indicate that the regional geology is a key factor to determine soil geochemical baselines. The composition of soils was generally similar to the bedrock composition, and differences between the analyzed soil layers were statistically insignificant. The elemental composition of soils is influenced by acidity/alkalinity levels, particle-size composition and organic matter content. The concentrations of Ni, Cr and lanthanoids depended on the soil pH, with Ni and Cr being more mobile in acid medium and the light lanthanoids -in alkaline medium. For that reason, Ni and Cr were leached from the acid layers and lanthanoids -from alkaline layers. As a result, the acid soils that were relatively enriched in organic matter were distinguished by the high concentrations of lanthanoids, Pb and Hg and the low concentrations of Ni and Cr. The statistical analysis showed a negative correlation between the concentrations of Cu, Ni, Mn, Fe 2 O 3 and the content of sand and a positive correlation with the contents of silt fraction. The highest concentrations of Hg, Pb and lathanoids were found in soils with a high organic matter content.
As compared to the other islands of the Arctic, the soils of Alexandra Land had high concentrations of Cu, Mn, Co and Fe and low concentrations of Hg, Pb and Cd. Such properties of the studied soils were predetermined by the composition  (Plichta et al. 1991); 5 -Longyearbyen, Spitsbergen, median values (Wojtun et al. 2019); 6 -Svalbard, median values (Halbach et al. 2017); 7 -Severnaya Zemlya Archipelago, mean values (Zhulidov et al 1997). < DL -below the detection limit 1 Oxide contents have been recalculated into pure element contents 2 In the surface layer