INTRODUCTION

The Barents Sea is a relatively shallow epicontinental basin of the Arctic Ocean. It is linked with the surrounding seas and Atlantic Ocean. The surface of the Barents Sea floor has an uneven topography owing to the combination of isometric or extended submarine rises and intervening trenches and depressions (Levitan et al., 2007; Nikiforov and Koshel, 2010; Sorokhtin et al., 2016). The main types of modern bottom sediments of the Barents Sea are pelitic ooze occupying over 50% of its area, as well as sandy aleurites, aleuritic sands, and aleuritic pelites covering 30–32% area of this basin (Klenova, 1960; Pavlidis, 1995; Tarasov et al., 2000; Gurevich, 2002; Denisenko, 2013). The terrigenous material in the Barents Sea was provided by the erosion of seamountsFootnote 1, coastal solifluction and abrasion, and glacial exaration (Elverhøi et al., 1989; Levitan et al., 2007). It was also sourced from the suspended river load, ice, and atmospheric fallouts (Aibulatov et al., 1999; Mityaev and Gerasimova, 2018; Shevchenko et al., 1997; Vasil’ev et al., 2013). According to (Aibulatov et al., 1999, p. 529), “… the sources of suspended matter and areas of its deposition are mainly located within the sea. External sources of the suspended particulate matter are the White and Kara seas, as well as the Nordkap branch of the Gulf Stream.”

The Barents Sea is characterized by a complex system of surface currents (Gidrometeorologiya …, 1990; Vogt and Knies, 2009 and others) (Fig. 1a). The most intense among them is the Nordkap Current, which enters from the Atlantic Ocean and is subdivided eastward into several branches. Waters of the Arctic Basin are directed to the south of the Franz Josef Land Archipelago (FJL) and along the eastern part of Spitsbergen. The Makarov Current enters the Barents Sea from the northeast, while the Litke Current enters the Barents Sea from the Kara Gate. Movement of the “heavy” bottom brines, which are enriched in suspended particulate matter and formed by brine squeezing during ice formation on the sea surface, has a different configuration (Lisitzin, 2001) (Fig. 1b).

Fig. 1.
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(a) Location of stations during Cruise 67 of the R/V Akademik Mstislav Keldysh (Politova et al., 2018) and scheme of surface currents in the Barents Sea basin (Gidrometeorologiya …, 1990; Vogt and Knies, 2009; and others). (b) Main pathways of bottom flows enriched in brine suspension, modified after (Lisitzin, 2001). (1) Currents entering the Barents Sea from the Atlantic Ocean; (2) the same, from the Arctic Basin; (3) possible pathways of brines (“heavy liquids”) along bottom depressions; (4) general direction of current along the slope and movement of sedimentary material by contour currents. Gray color in Fig. 1b shows the depth regions over 300 m.

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The Barents Sea has a heterogeneous drainage area. The Kola Peninsula is made up mainly of Archean granite gneisses (Geologicheskaya …, 2001). Its northeastern margin is composed of the Late Proterozoic fold zone, which includes diverse metasedimentary rocks. The Pai-Khoi Range, northern Urals, and southern Novaya Zemlya area consist of Paleozoic sedimentary, magmatic, and metamorphic complexes (Geologicheskoe …, 1984). The eastern part of FJL is composed of the Triassic–Jurassic terrigenous rocks. The central and western parts of the FJL consist of Cretaceous basalts and dolerites (Geology …, 1998; Stolbov, 2005), as well as Cenozoic terrigenous rocks. The Novaya Zemlya Archipelago is a continuation of the Uralian fold structures. Its northern part consists of the Lower–Middle Proterozoic marbles, crystalline schists, and amphibolites, as well as the Upper Proterozoic and Cambrian–Silurian sediments intruded by granitoids. The southern part is dominated by the Late Riphean–Vendian flyschoid sediments overlapped by Paleozoic rocks (Geologicheskoe …, 1984; Geologiya…, 1967). The Ushakov and Vize islands are made up of the Lower Cretaceous clastic rocks (Geologicheskoe …, 1984; Geologiya…, 1967), which are also exposed on the seafloor around the islands (Levitan et al., 2007 and others). The eastern zone of Spitsbergen is made up of the Grenville basement and cover rocks (Upper Proterozoic and Paleozoic). Its central part consists of the Upper Riphean and Vendian metasedimentary and metavolcanic rocks and the Lower Paleozoic carbonate rocks. The western zone of Spitsbergen comprises Caledonian terrigenous and carbonate rocks, Carboniferous–Permian evaporites, and Mesozoic clastic rocks (Geologiya …, 1970; Geologicheskoe …, 1984). According to (Levitan et al., 1999, 2007), Novaya Zemlya serves as the main source of epidote; Franz Josef Land is the source of clinopyroxenes; and the North Kara Rise delivered garnet and iron hydroxides. Hornblende is likely delivered to the modern bottom sediments through the erosion of Mesozoic rocks of the Admiralteiskii Swell.

At present, we have insufficient data on the distribution of rare and trace elements in the modern bottom sediments of the Barents Sea. As cited in (Vasil’ev et al., 2013, p. 94), “Trace elements in sediments were determined by the spectral semiquantitative analysis. Due to a small number of analyses, the trace element distribution can only be estimated in general features.” The aim of this work is to fill this gap.

This paper analyzes the content and distribution of some rare and trace elements in samples of the modern bottom sediments of the Barents Sea (pelitic, aleuritic–pelitic, and sandy–aleuritic–pelitic oozes; in total, 34 samples), which were taken by bottom grabFootnote 2 during Cruise 67 of the R/V Akademik Mstislav Keldysh in September 2016 (Politova, 2018) (Fig. 1a). We also analyzed the correlation of these elements with the contents of the fine pelite (<0.001 mm) fraction and Сorg.

Rare and trace elements were determined by the ICP-MS method at the Institute of Geology and Geochemistry of the Ural Branch of the Russian Academy of Sciences (analysts D.V. Kiseleva, N.V. Chgerednichenko, and L.K. Deryugina) using the technique reported in (Maslov et al., 2011). Prior to analysis, >1-mm fraction was sieved out. The combined grain-size analysis was carried out at the Institute of Oceanology of the Russian Academy of Sciences. The Corg content was determined with an AN-7560 express analyzer (analyst L.V. Demina, Institute of Oceanology of RAS) by measuring the CO2 content in the course of sample burning (Т ~ 900°С) in the CO2-free air jet.

In the discussion presented below, the obtained data are grouped into test sites: (1) “Pechora Sea” (st. 5407, 5408); (2) “Western slope of the Kanin Shoal” (station 5411); (3) “Central Barents Sea (Stockman)” (st. 5412–5417, 5421); (4) “Russian Gavan” Fjord (st. 5422, 5424, 5427); (5) “Medvezhinsky Trough” (st. 5429–5431, 5433, 5434); (6) area south of Spitsbergen (st. 5440, 5441); (7) “Kola Meridian” (st. 5442–5444); (8) “Spitsbergen–Franz Josef Land Archipelago” (st. 5445–5448, 5450, 5452); (9) “Cambridge Strait” (in the vicinity of FJL) (st. 5453–5456).

BRIFE LITHOLOGICAL DESCRIPTION OF MODERN BOTTOM SEDIMENTS IN THE BARENTS SEA

According to the data in (Gurevich, 1995; Khasankaev, 1978; Levitan et al., 2000, 2003b, 2007; Tarasov, 1996), significant amounts of boulder–pebble material among surface sediments of the Pechora Sea occur only in Cheshskaya Bay. The central part of the sea is dominated by the medium- to fine-grained sands, as well as their aleuritic varieties. Fine clayey aleurites and aleuritic–pelitic ooze are uncommon, being confined to the depressions or exposures of Holocene sediments. The light fraction of sediments has sufficiently uniform composition (quartz, K-feldspars, medium and acid plagioclases).

Heavy metals are dominated by black ore minerals, garnet, hornblende, and epidote. Zircon, clinopyroxene, siderite, apatite, and titanite occur and sometimes play a significant role. Garnet enriches sediments in the western part of the sea, which is related to the erosion of granite-metamorphic complexes of the Baltic Shield. The elevated content of amphiboles is confined to the central part of the basin. Epidote is mainly accumulated in sediments from the eastern part, which indicates a contribution of greenstone-altered Paleozoic complexes of the Polar Urals, Pai- Khoi, Vaigach, and Novaya Zemlya. The elevated content of clinopyroxenes is observed south of Southern Island (Novaya Zemlya), where they were sourced from the Lower Paleozoic mafic volcanic rocks. According to the presented data, the Pechora Sea can be subdivided into several terrigenous–mineralogical provinces (Levitan et al., 2007): Vaigach (zircon–garnet–epidote–ore mineral association), southern Novaya Zemlya (epidote–ore mineral–clinopyroxene–garnet association), western Pechora (epidote–garnet–ore mineral association), central Pechora (ore mineral–garnet–epidote association), and eastern Pechora (hornblende–garnet–ore mineral–epidote association). The mineral composition of the light and heavy fractions gives grounds to suggest an essentially granitoid composition of their provenance, at subordinate contribution of volcanogenic and volcanosedimentary rocks from the northern termination of the Urals Fold Belt.

Clay minerals in the surface layer of bottom sediments of the Pechora Sea are represented by the uniform association of kaolinite, Mg–Fe chlorite, and hydromica, with subordinate smectite (Levitan et al., 2003b).

The St. Anna Trough floor is covered by the pelitic and aleuritic–pelitic ooze, which gives way to the fine aleurite ooze and coarse aleurites on the slope (Levitan et al., 2007). Content of the pelite material in sediments reaches 50–70%. The light fraction of modern bottom sediments is dominated by quartz, K-feldspar, plagioclases, and rock fragments. Three mineral associations are distinguished based on the proportions of quartz and feldspar in the fine sand fraction (Levitan et al., 1999). Sediments covering the western slope and almost entire area of the trough floor consist of quartz and rock fragments, and feldspars are almost completely absent (quartz/feldspar ratio is 5.0 or higher). The major heavy minerals are epidote, clinopyroxene, black ore minerals, common hornblende, and garnet. The maximum epidote/clinopyroxene ratio was found in sediments surrounding the northern termination of Northern Island of Novaya Zemlya (Levitan et al., 1999).

According to the lithological and grain-size composition of surface sediments of the St. Anna Trough and the mineral composition of the fine sand to coarse aleurite and subcolloid fractions, the trough is subdivided into different facies zones: central zone, eastern and western slopes, as well as areas adjacent to FJL, Novaya Zemlya, and North Kara Rise (Levitan et al., 2007). According to concepts proposed by M.A. Levitan and colleagues, the main source of quartz and rock fragments for the fine sand fraction is FJL, while feldspars were supplied from the North Kara Rise. The presence of rock fragments in the west and southwest of the trough is interpreted as a result of iceberg rafting.

The sources of chlorite and illite are the North Kara Rise and Novaya Zemlya. Kaolinite was derived by the erosion of Triassic sandstones (with the kaolinite cement) exposed on the FJL. The presence of smectite in sediments of the trough, which is located between the zones of essentially kaolinite association in the west and chlorite–illite association in the east, could be caused, according to (Levitan et al., 2007 and others), by a decrease of the contents of kaolinite, chlorite, and illite with distance from their source and a decrease of diluting effect. It is believed that smectite could be derived from: (1) weathering crust formed after the FJL trap rocks; (2) Upper Jurassic bituminous shales, which are exposed on the seafloor surface in the Admiralteiskii Swell area; and (3) Atlantic waters enriched in smectite.

According to (Murdmaa et al., 2006), Holocene sediments in the central and eastern parts of the Barents Sea contain up to 22–47% illite. The amount of chlorite and kaolinite in the clay mineral association varies from 29 to 65%, while smectite occurs in subordinate amount. According to the foraminiferal distribution, the considered sediments could be ascribed to three facies types (Murdmaa et al., 2006): (1) facies with numerous benthic, in some cases, planktic, species (eastern branch of the Franz–Victoria Trough, Persey Trough, and some other areas) (these sediments are located in the influence zone of the Atlantic waters); (2) facies represented by the alternation of foraminifera-rich and foraminifera-free intervals likely related to the freshening (these sediments are developed south of FJL and in the Western Novaya Zemlya Trough); and (3) facies almost devoid of foraminifers, likely, owing to the low sedimentation rate, influence of bottom currents, or ecological stress (this facies is typical of deep-water plains and rises). In general, the accumulation of Holocene fine-grained sediments is controlled by the following factors: influx of material with the glacial thawed waters, drifting ices, rivers, and others. Biogenic processes also contribute to the formation of bottom sediments (Murdmaa et al., 2006).

According to the data obtained during Cruise 67 of the R/V Akademik Mstislav Keldysh, the upper part (0–1 cm) of modern bottom sediments of the “Pechora Sea” test site consists of the oxidized, mainly sandy sediments with the admixture of olive-brown (2.5Y/4/3)Footnote 3 or dark gray-brown (2.5Y/4/2) aleurite and pelite fraction. Sediments were studied at two stations, where the pelitic material accounted for 14 to 34%.

On the “western slope of the Kanin Shoal” test site, pelitic ooze with admixture of shell material (<2%), numerous polychaeta or their sheaths, were collected by bottom corer. The upper layer (0–2 cm) is olive-brown (2.5Y/4/4), oxidized and hydrated. The content of pelite fraction is 67%, including 41% fine pelite.

The Central Barents Sea (Shtokman) test site contains the pelitic and sandy–aleuritic–pelitic ooze; two stations contain mixed sediments. One station contains the gravel–pebble sediments with admixture of mixed sediments. Another station contains the gravel–pebble sediments with the fine-grained admixture. The pelitic ooze contains gravel and pebble admixture. The sediments comprise Fe–Mn crusts, tubes, and nodules, as well as numerous frequently ferruginated polychaetes and their sheaths. In addition, there are fragments of shells (<3%). The upper sediment layer (0–1 cm) is oxidized, olive-brown (2.5Y/4/3), olive-gray (5Y/4/2), or intense dark gray-brown (5Y/3/2) and hydrated. Sandy–aleuritic–pelitic oozes have saturated dark gray-brown (5Y/3/2) color and contain significant admixture of gravel, pebble, and boulder material, mainly rounded and well rounded. These oozes also contain shell detritus (<3%) and a small amount of polychaetes and their sheaths. The content of pelite fraction in samples of this test site varies from 31 to 90%.

In Russkaya Gavan Fjord (Northern Island, Novaya Zemlya Archipelago) and near it, we sampled the pelitic and aleuritic–pelitic oozes (in the bay and at its exit), as well as sediments of the mixed type (away from the bay). In the former sector, the upper layer (0–1 cm) is represented by the pelitic gray (5Y/5/1), homogenous, soft, and very ductile ooze. It contains rare shells and hydrotroilite films. Mixed sediments have dark, greenish gray (Gley1/4/10Y) or dark gray (5Y/4/1) color and contain well-rounded gravel, pebble, and boulder material. The sediments also contain admixture of shell material, polychaete, and their sheaths. The content of pelite fraction varies from 46 to 94%.

The sandy–aleuritic–pelitic, aleuritic–pelitic, and pelitic ooze (along the trough transect), as well as silted sands with aleurite admixture (on the flexure of continental slope) were sampled in the “Medvezhinsky Trough” during Cruise 67 of the R/V Akademik Mstislav Keldysh. The upper layer (0–1 cm) in two former sediment types is oxidized olive grey (5Y/4/2) and sometimes consists of the sandy–aleuritic–pelitic sediments with admixture of gravel, pebble, and boulder material. This layer is liquid and contains polychaetes and their sheaths, some of which are covered by ferruginated crusts. In the pelitic ooze, the upper layer (0–1 cm) is oxidized, dark gray brown (2.5Y/4/2), and liquid. The layer contains a small amount of polychatetes and their sheaths, ferruginated nodules, tubes, and crusts. The content of pelite fraction in samples of the given test site varies from 34 to 91%.

The “Spitsbergen–Franz Josef Land” latitudinal section contains the silty and silted sands, gravel–sandy–pelitic, sandy–aleuritic–pelitic, and pelitic ooze. In this work, we analyzed only sediments of the pelitic and mixed grain-size composition developed south of Spitsbergen. The sediments of mixed composition are olive-gray (5Y/4/2). They contain polychaetes and their sheaths, intact valves (0.5–1.5 cm), and shell detritus. The upper layer (0–1 cm) of pelitic ooze is oxidized, dark gray-brown (2.5Y/4/2), and liquid. Sediments of this layer contain a small amount of polychaetes and their sheaths. The content of pelite fraction in samples varies from 15 to 93%.

The aleuritic–pelitic ooze and mixed sediments were sampled at the “Kola Meridian” test site. The upper layer (0–2 cm) of the former sediment is oxidized, olive-gray (5Y/4/2), and liquid. The layer contains numerous polychaetes and their sheaths. The mixed sediments are also olive-gray (5Y/4/2). They contain rounded and moderately rounded gravel-pebble fragments and insignificant admixture (<1%) of shell detritus. These sediments contain numerous polychaetes and their sheaths and are frequently ferruginated. There are also Fe–Mn crusts and tubes. Modern bottom sediments of the “Kola Meridian” test site contain from 26 to 68% pelite fraction.

In the “Spitsbergen–Franz Josef Land” latitudinal section, sediments are diverse and represented by both sandy–aleuritic–pelitic and pelitic oozes, and sediments of the mixed type, while sediments near the northern termination of Spitsbergen are composed of the gravel–pebble material. In the sandy–aleuritic–pelitic sediments, we also found the admixture of subrounded gravel–pebble–boulder material, rare shell fragments (<3%), as well as sporadic Fe–Mn crusts and tubes. The upper (0–1 to 2 cm) layer of these sediments is oxidized and dark gray-brown (2.5Y/4/2 or 10YR/3/2). The upper layer (0–2 cm) of the pelitic ooze is also oxidized, dark gray-brown (10YR/3/2) or dark gray-brown (10YR/4/2), and liquid. The sediments contain a small amount of polychaetes and their sheaths, as well as scarce shells. The content of pelite fraction in samples from this test site varies from 5 to 97%.

In the Cambridge Strait, the upper sediment layer (0–1 cm) is represented by the oxidized liquid pelitic ooze of dark gray-brown color (10YR/3/2 or 10YR/4/2). The samples contain variable amount of polychaetes and their ferruginated sheaths. The sediments are well sorted. The content of pelite fraction in modern bottom sediments of the Cambridge Strait varies from 81 to 93%.

The distribution of different grain-size fractions in sediments of some test sites is shown in Fig. 2. The content of fine pelite fraction in the studied samples of bottom sediments of the Barents Sea varies, as shown above, from 2.8% to ~60% (average 34.6%) (Table 1). The average Сorg content is 1.12% (minimum 0.13%, maximum 2.62%) (Table 2).

Fig. 2.
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Distribution of grain-size fractions in the modern BS of the “Shtokman” (st. 5415), “Medvezhinsky Trough” (st. 5430), “Kola Meridian” (st. 5444), and “Cambridge Strait” (st. 5454) test sites. (1) Gravel; (2) sand; (3) aleurite; (4) pelite.

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Table 1.   Results of the combined grain-size analysis of modern bottom sediments sampled during Cruise 67 of the R/V Akademik Mstislav Keldysh, %
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Table 2.   Content of Сorg in the modern BS of the Barents Sea
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DISTRIBUTION OF SOME RARE AND TRACE ELEMENTS IN MODERN BOTTOM SEDIMENTS OF THE BARENTS SEA

Only data on the Cu, Ni, Zn, Pb, Co, Cr, and Hg distribution have been reported for modern bottom sediments of the Barents Sea (Novikov and Zhilin, 2016). These data were obtained for samples collected in the period from 1998 to 2015 at many stations. The scale of the Norwegian Pollution Control Authority for the coastal zone of the Norwegian Sea (Bakke et al., 2007) was used as the regional background by M.A. Novikov and A.Yu. Zhilin. However, it was noted that the presented Ni and Cr contents for the Barents Sea need to be corrected.

It has been established that the relatively high Cr and Ni contents in bottom sediments are sufficiently evenly distributed over the entire Barents Sea (Novikov and Zhilin, 2016). Elevated heavy metal contents in modern bottom sediments are typical of slopes of the Medvezhinsky Bank, areas of the Medvezhinsky and Central troughs, Rybachii and Kil’din banks, coastal regions of the southwestern part of the sea, Murmansk Bank, and Western Novaya Zemlya Trough. High Cu, Ni, Zn, and Pb contents are observed in bottom sediments of the coastal band west of Kola Fjord. Average Cu, Ni, Zn, and Pb contents in this area are, respectively, 1.78, 1.15, 1.21, and 1.73 times higher than in bottom sediments from other part of the Barents Sea. According to (Novikov and Zhilin, 2016), this indicates an anthropogenic pollution of coastal sediments by the continental runoff from the northwestern Kola Peninsula.

Analysis of the Cu/Ni ratio in samples of modern bottom sediments, atmospheric emissions from metallurgical plants of the Kola Peninsula, sedimentary cover of highlands in this region, atmospheric fallouts, and water samples of the Barents Sea allowed us to conclude that bottom sediments of the Barents Sea are enriched in Ni “… relative to the terrigenous material.” In contrast, they are depleted in Co “…relative to the terrigenous material.” The main conclusion made in (Novikov and Zhilin, 2016, p. 84) is that “… the modern level of Cu, Ni, and Co contents in the BSFootnote 4 over the most part of the Barents Sea is not related to the activity of industrial enterprises of the Kola Peninsula.” Elevated Co and Pb contents in the BS sampled along the “Kola Meridian” (33°30' E) are caused by the heavy metal influx with waters of the Nordkap Current. In general, the heavy metal distribution in the modern BS of the Barents Sea is controlled by the global geochemical background overprinted by regional component. The background is formed mainly by influx of the dissolved and suspended lithogenic material of the Nordkap Current (Novikov and Zhilin, 2016).

Comparison of Сr, Ni, Cu, Zn, Cd, and Pb Contents in Modern Bottom Sediments from Different Test Sites with Background Concentrations

In order to obtain comparable conclusions, following (Novikov and Zhilin, 2016), we accepted the values reported in (Bakke et al., 2007) as background concentrations, although this choice is not perfect. Average Сr, Ni, Cu, Zn, Cd, and Pb contents in the modern BS from different test sites and their relationships with background concentrations are given in Table 3. As follows from the consideration of these data, the contents of all aforementioned metals in the Pechora Sea are much lower than the background contents. In sediments on the western slope of the Kanin Shoal, the Cu, Zn, Cd, and Pb contents correspond to 0.44–0.67 relative to the background value. The Ni content is more than two times higher than the background value, while the Cr content is close to the background value. At the Shtokman test site, the Cr and Ni contents are slightly higher than the background values, whereas concentrations of other elements are much lower. Approximately the same pattern is typical of bottom sediments at the “Russkaya Gavan” test site. In modern bottom sediments of the “Medvezhinsky Trough,” only the Ni content slight exceeds the background value.

Table 3.   Average content (ppm) of some heavy metals in the modern BS from different areas of the Barents Sea and the average content normalized to the regional background value of these metals (Bakke et al., 2007)
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Contents of all aforementioned elements in bottom sediments of the area located south of Spitsbergen are close to or lower than the background contents. According to our data, average Ni and Cr contents in the BS at the “Kola Meridian” test site correspond to 1.03 ± 0.52 and 0.98 ± 0.50 relative to the background value, whereas average contents of other elements are slightly lower than background contents. Modern bottom sediments of the “Spitsbergen–FJL” latitudinal section are characterized by slightly higher average Ni content compared to the background level. The average Cr content in them is comparable with the content of this element in background sediments (~73 ± 15 and 70 ppm), while average contents of Cu, Zn, Cd, and Pb are below the threshold values between the background and anomalous concentrations. Slightly different pattern is observed for modern bottom sediments sampled in the Cambridge Strait. Average Cu and Ni contents in these sediments are much higher than background values (by ~2.2 and ~1.9 times, respectively). The average Cr content is ~88 ± 6 ppm, whereas the background value is 70 ppm (Bakke et al., 2007). Average contents of other elements, as at other test sites, are lower than the background contents.

Comparison of Rare and Trace Element Contents in Modern Bottom Sediments from Different Test Sites and PAAS

Relative to PAAS (Taylor and McLennan, 1985), trace element contents in the modern BS of the Barents Sea are divided into the following gradations: (1) less than 0.75 × PAAS; (2) 0.75–0.9 × PAAS; (3) 0.9–1.1 × PAAS; (4) 1.1–1.5 × PAAS; and (5) more than 1.5 × PAAS. According to these gradations, only the average Sr content in samples taken from the “Pechora Sea” test site corresponds to the gradation of more than 0.75 × PAAS, whereas concentrations of other trace elements are lower (Fig. 3a). In sediments from the western slope of the Kanin Shoal, only the Mn content is comparable with that of PAAS. Average V and Ni contents are, respectively, 1.22 and 1.19 × PAAS; contents of Zn, Sr, and Pb correspond to the gradation of 0.75–0.9 × PAAS; and contents of other elements are less than 0.75 × PAAS. In the modern BS of the “Shtokman” test site, average contents of Zn, Sr, Eu, and Gd correspond to the gradation 0.75–0.9 × PAAS; contents of Mo and V fall within 1.1–1.5 × PAAS; and contents of other rare and trace elements are less than 0.75 × PAAS (Fig. 3b).

Fig. 3.
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PAAS-normalized trace element pattern in bottom sediments of the “Pechora Sea” (a), “Shtokman” (b), “Russkaya Gavan”, and (c) “Medvezhinsky trough” (d).

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Bottom sediments of the “Russkaya Gavan” test site are characterized by a wider spectrum of trace element gradations. In particular, average contents of Ni, Ga, and Eu correspond to the gradation 0.75–0.9 × PAAS; contents of V, Zn, and Sr, to the gradation 1.1–1.5 × PAAS. The average Mo content reaches 1.59 × PAAS, while contents of other elements are less than 0.75 × PAAS (Fig. 3c). In the modern BS of the “Medvezhinsky Trough” test site, average V, Eu, and Gd contents correspond to 0.75–0.9 × PAAS; Mo and Pb contents, to 1.1–1.5 × PAAS; and Sr content, to1.1–1.5 × PAAS (Fig. 3d).

In samples taken south of Spitsbergen, the V, Gd, and Pb contents fall in the interval of 0.75–0.9 × PAAS, whereas the average Sr content is slightly higher (1.34 × PAAS). Average contents of other trace elements are less than 0.75 × PAAS (Fig. 4a).

Fig. 4.
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PAAS-normalized trace element pattern in the modern BS south of Spitsbergen (a), as well as at the “Kola Meridian” (b), “Spitsbergen–FJL” (c), and “Cambridge Strait” (d).

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Bottom sediments of the “Kola Meridian” test site are characterized by the following average contents of rare and trace elements: V and Pb contents are within 0.75–0.9 × PAAS; other elements, less than 0.75 × PAAS (Fig. 4b). Bottom sediments of the “Spitsbergen–FJL” latitudinal section are characterized by more significant variations of average trace element contents. The Sc, Co, Zn, Ga, Sr, Eu, Gd, and U contents are within 0.75–0.9 × PAAS. Slightly higher contents (1.1–1.5 × PAAS) are typical of Pb and Bi (Fig. 4c). The average content of V is 1.35 × PAAS (grade 4), while that of Mo reaches 7.79 × PAAS. Minimum and maximum Mo contents are 0.93 × PAAS and 30.74 × PAAS, respectively. Excluding the latter value as anomalous yields the average Moav of 3.20 × PAAS, which is also much higher than the contents established in BS samples from other test sites.

In the modern BS of the Cambridge Strait, average contents of Li, Rb, Y, Zr, Nb, Sn, Cs, Ba, La, Sm, Yb, Hf, Pb, Bi, Th, and U correspond to <0.75 × PAAS. Higher values (0.75–0.9 × PAAS) are typical of Cr, Ga, and Sr (Fig. 4d). Average contents of Ni, Eu, and Gd correspond to gradation 3; i.e., they are comparable with concentrations of these elements in PAAS. Sufficiently high average contents were determined for Sc, Co, and Zn (gradation 4). Concentrations of Cu and Mo reach more than 1.5 × PAAS. However, average contents of these elements (relative to PAAS) differ by almost an order of magnitude. The Cu content in samples of the given test site varies from 1.24 to 1.81 × PAAS (on average, 1.55 × PAAS). The average Mo content in the modern BS of the Cambridge Strait is 13.72 × PAAS (minimum 8.17 × PAAS, maximum 29 × PAAS). Excluding sample 5454 with the “anomalous” highest Mo content (29.23 × PAAS) yields Moav of 10.62 × PAAS.

In general, the obtained data are consistent with the concept that the distribution of heavy metals and some rare and trace elements in bottom sediments of the Barents Sea are mainly controlled by the global geochemical background (Novikov and Zhilin, 2016). At the same time, the local factors, particularly, the content of pelite fraction and organic matter in sediments also contributed to their contents.

Correlation of Some Rare and Trace Elements in Modern Bottom Sediments of the Barents Sea with the Fine Pelite Fraction and Corg

In this section, we discuss the results related to a great number of samples and compare them with other sections of our work. Concentrations of most rare and trace elements in the modern BS of the Barents Sea (Sc, V, Cr, Ni, Y, Zr, Nb, Mo, Hf, Th, U, and REE) show a moderate positive correlation with the fine pelite fraction in these sediments. In particular, the coefficient of correlation (r) between the contents of Sc and the fine pelite fraction in analyzed samples is 0.63 (Fig. 5). For V and Cr, the value r is slightly higher (0.71 and 0.72, respectively). Correlation between Hf and Zr contents and the fine pelite fraction in these samples is poor (r = 0.58 and 0.59, respectively). Approximately the same r values are typical of Nb and Y. U, Th, and Mo show a poor positive correlation with the fine pelite fraction in the modern BS (r = 0.38, 0.36, and 0.41, respectively). The same correlation (r = 0.50) is typical of the total rare-earth element (∑REE) content. A sufficiently poor positive correlation with the pelite fraction in bottom sediments is typical of Cu, Zn, and Pb (0.57, 0.67, and 0.42, respectively).

Fig. 5.
figure 5

Correlation of trace element contents with the content of pelite fraction in the modern BS of the Barents Sea.

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Based on the coefficient of correlation between element concentration and Corg in bottom sediments, all studied rare and trace elements can be subdivided into three groups. For example, V, Cr, and Ni characterized by the moderate positive correlation with Сorg (0.61 < r < 0.67) belong to the first group (Fig. 6). The second group (Sc, Hf, Zr, Nb, U, Th, Y, and REE) has correlation coefficient between 0.34 (Sc) and 0.52 (Nb). Correlation between Сorg and ∑REE is low (r = 0.29). This means that REEs in the modern BS of the Barents Sea are mainly linked with the lithogenic components. This group also includes Pb, Zn, and Cu (r = 0.40, 0.49, and 0.32, respectively), which show a poor positive correlation with Сorg. The third group includes Мo having no correlation with Сorg (r = 0.11).

Fig. 6.
figure 6

Correlation of trace element contents with Сorg in the modern BS of the Barents Sea.

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In general, the obtained data are consistent with the results reported by Novikov and Zhilin (2016), who demonstrated that the Сorg content in bottom sediments of the Barents Sea varies from 0.13 to 3.76% (average, 1.58%), while the contents of Cu, Zn, Ni, Cr, Pb show a moderate positive correlation with Сorg.

DISTRIBUTION OF ELEMENT-INDICATORS OF SOURCE ROCK COMPLEXES OF THE FINE ALUMINOSILICICLASTICS (Sc, Th, Co, Cr, La, and Sm) IN MODERN BOTTOM SEDIMENTS

This section considers Sc, Th, Co, Cr, La, and Sm. According to (Cullers, 1995, 2002; Geochemistry …, 2003; Interpretatsiya …, 2001; Maslov et al., 2014; McLennan, 1989; Taylor and McLennan, 1985 and others), contents and ratios of these elements provide insight into the composition of source rocks of the fine-grained clastic material for bottom sediments (Table 4)Footnote 5. The average Sc content in the studied sampling varies from 3.8 ppm (“Pechora Sea” test site) to 23 ppm (“Cambridge Strait”). In samples taken at the test sites “West slope of the Kanin Shoal”, “Shtokman,” “Russkaya Gavan,” “Medvezhinsky Trough,” and “Spitsbergen–FJL,” average Sc contents are close (11.2‒12.7 ppm).

Table 4. Average, minimum, and maximum contents of Sc, Cr, Co, and Th in samples of the modern BS of the Barents Sea, ppm
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Table 5. Average, minimum, and maximum REE contents in samples of the modern BS of the Barents Sea, ppm
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Based on the average Sc content in samples, bottom sediments of the Barents Sea are subdivided into three groups: (a) sediments of the Pechora Sea (33.1‒33.8 ppm)Footnote 6, (b) “Medvezhinsky Trough” test site, area south of Spitsbergen, profiles “Kola Meridian” and “Spitsbergen–FJL” (58.8‒72.9 ppm); (c) bottom sediments taken at test sites “Western slope of the Kanin Shoal” (?),“Central Barents Sea,”, “Russkaya Gavan,” and “Cambridge Strait.” In the latter sediments, the average Cr content reaches almost 90 ppm, but remains lower than the Cr content in PAAS (110 ppm) (Taylor and McLennan, 1985)).

The minimum average Co content (~4.4 ppm) was found in samples of the modern BS from the “Pechora sea” test site, whereas the maximum value (~36.6 ppm) is typical of samples taken at the Cambridge Strait (the Co content in PAAS is 23 ppm) (Taylor and McLennan, 1985).

The average La content varies from 12.7 ppm (“Pechora Sea” test site) to 23.4 ppm (“Spitsbergen–FJL” latitudinal section), whereas PAAS contains 38.2 ppm La. At the same time, samples representing sediments from the test sites “Western slope of the Kanin Shoal,” “Shtokman,” “Russkaya Gavan,” “Medvezhinsky Trough,” and area south of Spitsbergen are characterized by close Laav values.

In samples from the “Pechora Sea” and “Kola Meridian” test sites, the average Sm content is ~2.1 and ~2.3 ppm, respectively. Surface bottom sediments taken at other test sites are characterized by slightly higher average Sm content (3.2‒3.9 ppm). The Sm content in PAAS is 5.6 ppm.

The maximum average Th content in the studied samples reaches ~7.1 ppm (14.6 ppm in PAAS), whereas the minimum value is around 2.5 ppm (“Pechora Sea” test site). The Th content in PAAS is ~14.6 ppm (Taylor and McLennan, 1985).

RARE-EARTH ELEMENT DISTRIBUTION IN MODERN BOTTOM SEDIMENTS OF THE BARENTS SEA

Like Sc, Th, Co, Cr, and some other trace elements, rare-earth elements are good indicators of rock complexes eroded in the paleodrainage areas (Condie and Wronkiewicz, 1990; Cullers, 1995; Geochemistry …, 2003; McLennan, 1989; Taylor and McLennan, 1985; Wronkiewicz and Condie, 1987 and others). Average, minimum, and maximum ∑REE values were determined in BS samples taken during Cruise 67 of the R/V Akademik Mstislav Keldysh from different test sites of the Barents Sea (Table 5). The total REE content in sandy rocks with admixture of the aleuritic and pelitic material from the “Pechora Sea” test site varies from ~57 to 66 ppm. The LREE/HREE ratio varies from 9.57 to 9.90. The chondrite-normalized, according to (Taylor and McLennan, 1985), average (La/Yb)N and (Gd/Yb)N are 10.61 and 1.91, respectively. The Eu anomaly is small negative (0.85). REE distribution patterns in the modern BS of the “Pechora Sea” test site are shown in Fig. 7.

Fig. 7.
figure 7

Chondrite-normalized REE patterns in the reference objects (upper left plot) and in the modern BS from different test sites of the Barents Sea. (PAAS) Post-Archean Australian Shales, after (Taylor and McLennan, 1988); (AR gr) Archean granites, (PR bas) Proterozoic basalts, (AR ttg) Archean tonalite–trondjhemite–granite associations; (AR kom) Archean komatiites, after (Condie, 1993).

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The pelitic ooze from the western slope of the Kanin Shoal is characterized by slightly higher ∑REE (98 ppm) compared to bottom sediments of the “Pechora Sea” test site. The LREE/HREE and (La/Yb)N ratios are, respectively, 8.77 and 9.54; (Gd/Yb)N = 1.89, and Eu/Eu* = 0.74.

At the “Central Barents Sea (Shtokman)” test site, the total REE in sediments varies from 52 to 117 ppm. The LREE/HREE ratio varies from 7.07 to 9.58 (7.07 and 7.52 in two samples, 8.41‒9.58 in other samples). The average (La/Yb)N is 10.60 (minimum 9.30, maximum 11.63), while \({\text{Eu/Eu}}_{{{\text{av}}}}^{*}\) is 0.77.

Modern bottom sediments of the “Russkaya Gavan” test site (pelitic, aleuritic‒pelitic, and mixed ooze) have approximately the same total REE (52–119 ppm) as sediments from the “Central Barents Sea” test site. The LREE/HREE ratio varies from 8.75 to 9.03. The (La/Yb)N and Eu/Eu* ratios vary from 7.63 to 9.60 and from 0.76 to 0.80, respectively; (Gd/Yb)Nav is 1.91 ± 0.15.

The total REE in the sandy–aleuritic–pelitic, aleuritic–pelitic, and pelitic oozes of the Medvezhinsky Trough varies from 78 to ~115 ppm. The average (La/Yb)N and (Gd/Yb)N is, respectively, 10.63 and 2.18. The \({\text{Eu/Eu}}_{{{\text{av}}}}^{*}\) is 0.76. The LREE/HREE ratio varies from 7.86 to 10.08.

In samples taken at stations 5440 (pebble with the pelite admixture) and 5441 (pelitic ooze) in the area south of Spitsbergen, the total REE content is ~67 ppm (due to the low content of the fine pelite fraction in this sample) and 124 ppm, respectively. Values of (La/Yb)N are, respectively, 8.47 and 0.72, while Eu/Eu* is 10.99 and 0.67, respectively. The LREE/HREE ratio varies from 7.58 to 8.59.

At the “Kola Meridian” test site, ∑REE in the modern BS varies from 52 to 78 ppm. The average (La/Yb)N is 9.35. In all three samples taken by bottom corer at this test site, the Eu/Eu* ratio is less than in samples from stations south of Spitsbergen. The LREE/HREE ratio varies from 8.25 to 8.58.

Diverse bottom sediments from the “Spitsbergen–Franz Josef Land Archipelago” are characterized by ∑REE from 87 to 127 ppm. The average (La/Yb)N is 11.26 (minimum 9.17, maximum 13.47). The Eu anomaly varies from 0.68 to 0.75; (Gd/Yb)Nav is 2.21; and LREE/HREE is 8.15‒10.41.

Pelitic oozes in the Cambridge Strait have the total REE content ranging from 88 to 94 ppm. The average (La/Yb)N in this area is much lower than in sediments from other test sites (~5.71). The Eu/Eu* ratio shows a narrow range (0.80‒0.81). These rocks are not depleted in HREE, and (Gd/Yb)Nav is 1.86. The LREE/HREE ratio varies from 5.19 to 6.02.

DISCUSSION AND CONCLUSIONS

It is suggested that the trace element contents and ratios remains practically unchanged during the transportation from provenances to sedimentation areas (Condie and Wronkiewicz, 1990; Cullers, 1995, 2002; Geochemistry …, 2003, McLennan, 1989; McLennan et al., 1990; McLennan and Taylor, 1991; Taylor and McLennan, 1985 and others). Felsic magmatic rocks (granites, granodiorites) are characterized by one to two orders of magnitude higher Th/Sc, La/Sm, La/Sc, Th/Co, and Th/Cr ratios compared to mafic rocks (Interpretatsiya …, 2001). At the same time, the Cr/Zr and Cr/V ratios and some other indicator ratios in the mafic magmatic rocks are one to two orders of magnitude higher compared to felsic rocks. Both these features, as well as some other attributes, are widely used in reconstructing the source rock composition for the modern BS from different seas, large river systems, and some other objects (Astakhov et al., 2015; Bayon et al., 2015 Censi et al., 2010; Chaillou et al., 2006; Chen et al., 2003; Damiani and Giorgetti, 2008; Dou et al., 2010; Douglas et al., 2003; Ingram and Lin, 2002; Martinez et al., 2009; Rachold, 1999; Song and Choi, 2009 and others).

To reconstruct the composition of sources rocks of the fine aluminosiliciclastics for modern bottom sediments of the Barents sea, we used a technique based on comparison of the ratios of rare and trace element-indicators in bottom sediments with values of these ratios in the reference geological objects: Archean granitoids (Kola Peninsula as an inferred source of the fine aluminosiliciclastics), Paleozoic andesites (fold structures of the Urals as an inferred source of the detrital material), as well as the Meso-Cenozoic basalts (FJL as the possible source)Footnote 7. The rare and trace element abundances in the reference objects were taken from (Condie, 1993); geochemical data on FJL were taken from (Chernysheva et al., 2003; Stolbov, 2005).

Analysis of the chondrite-normalized REE distribution in the fine-grained clastic sediments is of great importance as indicators of tectonic settings of the formation and source composition for post-Archean sediments (McLennan et al., 1990; Taylor and McLennan, 1985). Reconstruction of the source rock composition from REE patterns is based on the following fact: mafic magmatic rocks have sufficiently low LREE/HREE and (La/Yb)N ratios; they are devoid of pronounced Eu anomaly, whereas felsic rocks have higher LREE/HREE and (La/Yb)N values, as well as clearly expressed negative Eu anomaly (McLennan and Taylor, 1991; Taylor and McLennan, 1985). The (La/Yb)N values (<4) and weakly fractionated chondrite-normalized REE pattern indicate a leading role of the mafic magmatic rocks, whereas (La/Yb)N > 8 and, respectively, a steep slope of the REE pattern suggest the predominance of felsic magmatic rocks in the source area. The high (La/Yb)N value (≥20) indicates the presence of granitoids in the paleodrainage areas (Wronkiewicz and Condie, 1990).

In the Sc–Th/Sc diagram (Taylor and McLennan, 1985), data points of the modern BS collected in the Barents Sea at the former eight test sites fall between the reference composition points of potassic granitoids and diabases, being slightly displaced to the latter (Fig. 8). The composition points of bottom sediments of the “Cambridge Strait” test site are located in the vicinity of the reference data point of diabases and the FJL basalt composition field, which suggests that these sediments contain significant amount of fine-grained material derived through erosion of the magmatic mafic rocks of FJL.

Fig. 8.
figure 8

Position of data points of the modern BS from different test sites of the Barents Sea in the Sc–Th/Sc diagram. (1–9) Test sites: (1) “Pechora Sea”, (2) “Western slope of the Kanin shoal”, (3) “Shtokman”, (4) “Russkaya Gavan” Fjord, (5) “Medvezhinsky Trough”, (6) area south of Spitsbergen, (7) “Kola Meridian”, (8) “Spitsbergen–Franz Josef Land Archipelago”, (9) “Cambridge Strait”. Position of reference points of diabases, granodiorites, and K-granites, after (Roy and Roser, 2013; Schoenborn and Fedo, 2011). Composition field of the FJL basalts, after (Chernysheva et al., 2003; Stolbov, 2005).

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In the La/Sm–Sc/Th (Geochemistry …, 2003), La/Sc–Th/Co (Cullers, 2002), and La/Sc–Th/Cr diagrams, data points of bottom sediments from the Cambridge Strait are localized near or within the FJL composition field, as well as between the reference points of Meso-Cenozoic basalts and Paleozoic andesites (Fig. 9). This also points to the presence of significant amounts of erosion products of the mafic magmatic rocks. Composition points of modern sediments taken at other test sites plot between the data points of average compositions of Archean granitoids and Paleozoic andesites, being however closer to the latter. We may suggest that in these diagrams the average composition of Archean granitoids is geochemically close to that of granitoids of the Kola Peninsula, while the Paleozoic andesites are similar to the Paleozoic volcanogenic complexes of the northern Urals Fold Belt and Novaya Zemlya. Thus, with some degree of probability, modern bottom sediments in most part of the Barents Sea were mainly formed from the clastic material supplied from the south and southeast, as well as from external distal sources.

Fig. 9.
figure 9

Position of data points of the modern BS from different test sites and some reference objects (after (Condie, 1993)) in the La/Sm–Sc/Th, La/Sc–Th/Co, and La/Sc–Th/Cr diagrams. (1) Archean granitoids; (2) Paleozoic andesites; (3) Meso-Cenozoic basalts. For other symbols, see Fig. 8.

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In compliance with the scheme of surface currents, we compared (La/Yb)N in the modern BS of four regions: (1) Barents Sea part affected by the Atlantic waters (st. 5431, 5430, 5411, 5412, 5414, and 5416); (2) Barents Sea part affected by currents from the east and northeast (st. 5445, 5446, 5448, 5417, 5421, and 5413); (3) the FJL area (Cambridge Strait), and (4) area of Russkaya Gavan Fjord. It was established that bottom sediments of these areas have different (La/Yb)N ratio. In particular, bottom sediments of two former areas have (La/Yb)Nav 10.42 and 12.00. As was shown above, bottom sediments of the Cambridge Strait have much lower (La/Yb)Nav = 5.71, while those of Russkaya Gavan Fjord have an intermediate (La/Yb)Nav = 8.87.

In general, the average LREE/HREE and (La/Yb)N in the modern BS from different areas of the Barents Sea indicate that sediments of the “Cambridge Strait” test site contain significant amounts of the fine-grained aluminosiliciclastics formed through the erosion of mafic magmatic rocks.

In the (La/Yb)N–Eu/Eu* diagram (Geochemistry …, 2003), data points of the modern BS from all studied test sites define a compact cluster approximately at equal distance from rocks of the Archean TTG associations, Meso-Cenozoic basalts, FJL basalts, and Proterozoic granites (Fig. 10a). The Eu/Eu* values in all samples are slightly higher than in PAAS and are close to that in the Meso-Cenozoic andesites. Most BS samples from the Barents Sea are variably depleted in HREE. In terms of the (Gd/Yb)N ratio, some samples are similar to Proterozoic granitoids; other samples, to Archean TTG associations. In the (La/Yb)N–(Gd/Yb)N diagram, data points of samples taken at the “Cambridge Strait” test site are close to the composition field of the FJL basalts (Fig. 10b).

Fig. 10.
figure 10

Position of data points of the modern BS from different test sites and some reference objects (after (Condie, 1993)) in the (La/Yb)N–Eu/Eu* (a) and (La/Yb)N–(Gd/Yb)N (b) diagrams. (1–9) Test sites: (1) “Pechora Sea”, (2) “Western slope of the Kanin shoal”, (3) “Shtokman”, (4) “Russkaya Gavan” Fjord, (5) “Medvezhinsky Trough”, (6) area south of Spitsbergen, (7) “Kola Meridian”, (8) “Spitsbergen–Franz Josef Land Archipelago”, (9) “Cambridge Strait”; (10–14) reference objects: (10) Archean tonalite–trondhjemite–granite associations, (11) Proterozoic granites, (12) Meso-Cenozoic andesites, (13) Meso-Cenozoic basalts, (14) PAAS. For other symbols, see Fig. 8.

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Over the most part of the Barents Sea, the chondrite-normalized REE patterns in the fine-grained modern bottom ooze show no systematic variations, which is seen from the distribution of (La/Yb)N and Eu/Eu* along the profile from the Kola Peninsula to Russkaya Gavan Fjord (Fig. 11a). Another pattern is observed in the northern part of the Barents Sea, where bottom samples along the FJL–Spitsbergen section demonstrate a decrease of Eu/Eu* and, in contrast, increase of (La/Yb)N ratio (Fig. 11b). It is possible that in this part of the Barents Sea, erosion products of the mafic magmatic rocks are mixed with more mature material delivered from Spitsbergen.

Fig. 11.
figure 11

Variations of (La/Yb)N and Eu/Eu* in samples of the modern Bs collected between the Kola Peninsula and Russkaya Gavan Fjord (a), FJL and Spitsbergen (b). Station numbers are shown in the horizontal axis.

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Thus, new data suggest that the majority of modern fine-grained bottom sediments (pelitic, aleurite–pelitic, and sandy–aleuritic–pelitic ooze) from the Barents Sea area are made up of geochemically mature material, probably, derived from rocks of the Kola Peninsula and Spitsbergen (?). An essentially granitoid composition of source provinces of the Pechora Sea at subordinate role of volcanogenic sequences of the Pai- Khoi, Vaigach, and Novaya Zemlya was noted by Levitan et al. (2007). Bottom sediments of the Cambridge Strait are represented by less mature material, which was likely delivered to the basin as a result of the erosion of rock complexes (mainly basalts) of FJL. Northern Island of Novaya Zemlya likely was not a source of this material, because the modern fine-grained BS taken in Russkaya Gavan Fjord are characterized by the higher LREE/HREE and (La/Yb)N ratios compared to bottom sediments of the Cambridge Strait. At the same time, distribution of the heavy and clay minerals in the surface sediment layer of the Pechora Sea (Levitan et al., 2003а, 2003b, 2007, and others) suggests that Southern Island of Novaya Zemlya was the main source of clastic material for modern sediments of the southern Novaya Zemlya Trough and, likely, the entire eastern part of the Pechora Sea.