Geochemistry of mercury in surface sediments of the Kuril Basin of the Sea of Okhotsk, Kuril-Kamchatka Trench and adjacent abyssal plain and northwest part of the Bering Sea

Deep-Sea Research Part II xxx (xxxx) xxx–xxx

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Deep-Sea Research Part II journal homepage: www.elsevier.com/locate/dsr2

Geochemistry of mercury in surface sediments of the Kuril Basin of the Sea of Okhotsk, Kuril-Kamchatka Trench and adjacent abyssal plain and northwest part of the Bering Sea ⁎

Valentina V. Sattarova , Kirill I. Aksentov

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V.I.Il’ichev Pacific Oceanological Institute (POI), Far Eastern Branch of Russian Academy of Sciences (FEB RAS), 43, Baltiyskaya Str., 690041 Vladivostok, Russia

A R T I C L E I N F O

A B S T R A C T

Keywords: Mercury Deep-sea sediments Grain composition Kuril Basin Sea of Okhotsk Bering Sea Kuril-Kamchatka Trench Pacific Ocean

Mercury concentrations in surface sediments collected from the Northwestern Pacific were analyzed by mercury Zeeman atomic absorption spectrometer with high frequency modulation of light polarization and a pyrolysis attachment. The range of total Hg concentrations in sediments was 19–158 µg kg−1, with a mean of 77 µg kg−1 (n = 50). The variation in mercury concentrations in sandy deposits of the slopes was 19–79 µg kg−1 Hg; in clayey deposits from the Kuril Basin was 84–130 µg kg−1 Hg; in clayey deposits from slopes of the Kuril Basin was 44–84 µg kg−1 Hg; in clayey deposits from the abyssal area was 46–116 µg kg−1 Hg; and in clayey deposits from the slopes and bottom of the Kuril-Kamchatka Trench was 42–143 µg kg−1 Hg. Within the distribution of mercury across the study area, high mercury concentrations were observed in clayey sediments, which are enriched in organic matter and the remains of silicate phytoplankton. The Hg content of sandy deposits was minimal. The level of mercury in our deep-water sediments is somewhat overestimated by comparison to representative background values in clayey sediments from the impact areas (subject to anthropogenic pollution). Anomalies of mercury in bottom sediments near a hydrothermal source (Piip Volcano) have not been observed. The enrichment factor values at the stations range between 0.3 and 4.3. EF values of the most samples were generally more than 1, indicating that enrichment was by biogeochemical processes. Based upon four guideline values (ERL, ERM, ISQG and PEL) we can assume a minimal toxic mercury effect on the benthic marine biota.

1. Introduction It is important to study the processes governing the distribution and migration of mercury in the environment, because of its high toxicity. In recent years, interest in the behavior of mercury in the geological environment has not waned, but has grown significantly due to the widespread distribution of this element in the litho-, hydro- and atmosphere. Since the onset of the industrial period, anthropogenic emissions of mercury have increased and have significantly altered its global cycling (Fitzgerald et al., 2007; Schuster et al., 2002). The majority of the emissions originate from combustion of fossil fuels, particularly in Asian countries including China, India, and South and North Korea (Dastoor and Larocque, 2004; Pacyna and Pacyna, 2002). Therefore, significant volumes of mercury enter the Pacific Ocean and are transported by currents, which has serious implications for the resulting contaminant burdens in pelagic marine biota (Sunderland et al., 2009). The final destination of mercury migration is the bottom sediments (Selin, 2009).

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Nevertheless, the primary source of mercury is igneous activity, which encompasses volcanoes and related geological activities as well as land emissions from areas naturally enriched in mercury. The sediments located near the geothermal springs are significantly enriched in mercury, and have the highest concentrations compared to rocks and bottom sediments in the upper layers of the crust (Leal-Acosta et al., 2010; Rychagov et al., 2014). The study area is located in a subduction zone, which is characterized by volcanism and hydrothermal activities. Increased mercury emanations into the lower atmosphere near the surface water layer over seamounts were found in the Sea of Japan and the Bering Sea, which are associated with endogenous fluids (Astakhov et al., 2011; Kalinchuk and Astakhov, 2014). A mercury anomaly in the Quaternary sediments of the Deryugin Basin in the Sea of Okhotsk is produced by Hg fluxes from low-temperature hydrothermal or cold gas vents, which are localized along faults cutting across or bounding riftogenic spreading structures (Astakhov et al., 2007). Thus, there is already ground work on the mercury geochemistry in the northwestern part of the Pacific Ocean. However, despite the significant amounts of

Corresponding authors. E-mail addresses: [email protected] (V.V. Sattarova), [email protected] (K.I. Aksentov).

http://dx.doi.org/10.1016/j.dsr2.2017.09.002

0967-0645/ © 2017 Elsevier Ltd. All rights reserved.

Please cite this article as: Sattarova, V.V., Deep-Sea Research Part II (2017), http://dx.doi.org/10.1016/j.dsr2.2017.09.002

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V.V. Sattarova, K.I. Aksentov

Fig. 1. Map of the study areas (a) and the mercury concentrations in bottom sediments (b).

rocks. The majority of these rocks, dated by the K–Ar method, are Cretaceous in age (Gnibidenko et al., 1995). The East Kamchatka Current, a part of the Western Subarctic Gyre, flows parallel to and southward along the coast of the Kamchatka Peninsula. Some waters from the East Kamchatka Current flow into the Sea of Okhotsk through the passes between the northern Kuril Islands (Okazaki et al., 2004).

data in the literature, the behavior of mercury and many of the mechanisms of transformation and distribution that operate in natural waters still remain poorly understood. This research is a continuation of the geochemical exploration of bottom sediments in the northwestern part of the Pacific Ocean. It provides a representation of the level mercury concentration, its distribution and accumulation features.

2.2. Kuril-Kamchatka Trench 2. Study areas The Kuril–Kamchatka Trench (KKT) is located in the northwest Pacific Ocean. It spreads along the southeastern coast of Kamchatka in parallel to the Kuril Islands and connects with the Japan Trench (Fig. 1). The trench belongs to the subduction zone, which formed in the late Cretaceous and has created the Kuril island arc as well as the Kamchatka volcanic arc. The hydrography of the KKT area is complex (Arseniev and Leontieva, 1970) and influenced by several currents. The upper water masses are mainly influenced by the Oyashio and the Kuroshio (Tyler, 2002). The Oyashio flows from the Arctic southwards into the Pacific, the Kuroshio flows from East Taiwan towards the northeast. The conditions of sedimentation are determined by the morphological features, their position in the peripheral zone of the ocean, nearness to island arcs, modern active tectonic and volcanic processes. The pyroclastic and volcanic material enters the trench close to the Kuril Islands. The distribution and redistribution of this material occurs under conditions of a complex hydrodynamic field with the participation of underwater landslides and suspension flows and the transfer of volcanic ash in the

2.1. Kuril Basin (Sea of Okhotsk) The Kuril Basin has a triangular shape and strikes in a NE–SW direction (Fig. 1). This triangular outline is defined by Sakhalin–Hokkaido to the west, the Academy of Sciences Rise to the north and the Kuril Islands to the southeast. The Kuril Basin is approximately 700 km in length, has a maximum width of about 250 km in the southwest, and narrows to the northeast. The thick sedimentary cover masks the rugged basement morphology of the Kuril Basin, such that it is largely an abyssal plain outlined by the 3300-m isobath. The southeastern margin of the Kuril Basin has a complex structure because there are many seamounts in the form ridges. These seamounts are either volcanic chains or faulted arc basement. They occur as discrete volcanic edifices or volcanic ridges, which extend into the Kuril Basin for tens of kilometers, such as the volcanic ridge near the Bussol Strait (Gnibidenko et al., 1995; Baranov et al., 2002). The northern slope of the Kuril Basin is composed of extrusive, intrusive and metamorphic 2

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ignition (LOI) was determined by calculating the weight loss of the sample during drying in a muffle furnace at a temperature of ignition 950 °C to a constant weight. In order to determine the concentrations of the chemical elements we used the standard procedure outlined in Sattarova and Artemova (2015). The grain size was measured using the “Analysette 22 NanoTec” particle size analyzer (Fritsch, Germany). The samples were placed in a beaker and treated with hydrogen peroxide (30%) for a minimum of 24 h until digestion of organic matter had ceased and were then fully desalted and dispersed by adding 10 ml hexametaphosphate (10%), and by ultrasonic treatment for 30 min prior to measurement.

atmosphere (Tyler, 2002; Zenkevitch, 1963). 2.3. Bering Sea The Bering Sea is the third largest marginal sea in the world and consists of a deep (> 3500 m), relatively flat abyssal plain and a wide, flat continental shelf on the northern and eastern sides (Fig. 1). The Bering Sea is isolated from the open ocean by the active Aleutian volcanic island arc and Komandor Islands, and is connected in the north with the Chukchi Sea via the narrow Bering Strait. The northern part of the basin represents a slightly inclined flat shelf separated from the deepwater basin by the continental slope. The deepwater basin with a maximum depth of 3782 m is divided by the submarine Shirshov Ridge into the Komandor and Aleutian basins. The Shirshov Ridge extends in the southern direction from Cape Olyutorsky, and is 700 km long and 200 to 20 km wide in the northern and southern parts, respectively. The minimum water depth above the ridge crest is 233 m. The ridge towers above the bottom of the deepwater basin of the Bering Sea by 3000 m (Lisitzyn, 1966; Sancetta, 1981). The hydrological regime of the Bering Sea is influenced by subarctic climatic conditions, water exchange between the Chukchi Sea and Pacific Ocean, bottom topography, land drainage, and seasonal desalination of surface water due to ice melting. According to satellite data (Zhang et al., 2010), the seasonal sea ice mainly covers the northern and eastern shelf of the basin at present. The surface water circulation in the Bering Sea is an element of the subarctic cyclonic gyre of the Pacific Ocean. Waters of the strong Alaska Current enter the Bering Sea via straits in the Aleutian Islands chain. After transformation, they flow along the continental slope in a westerly direction (Stabeno et al., 1999). Terrigenous material is transported to the Bering Sea mainly by large rivers (Anadyr, Yukon, Kuskokwim), which drain two thirds of the entire drainage basin of the sea (Lisitzyn, 1966). A subordinate role belongs to solid material transported by small rivers and provided by coastal abrasion.

3.3. Normalization and statistical treatment of data Statistical analyses of the data were performed using StatSoft STATISTICA software package (Version 10). The raw data matrix was Zscore standardized and mid-range normalized to eliminate the influence of different units and ensure that each determined variable had equal weighting in the correlation and cluster analyses. For cluster analysis, we selected the Ward's Method, which was more successful in extracting clusters that are largely homogeneous and geochemically distinct from other clusters, compared to other methods such as the weighted pair-group average. Ward's Method is distinct from other linkage rules because it uses an analysis of variance approach to evaluate the distances between clusters. Applying the Euclidean distance as a distance measure and Ward's Method for a linkage rule produced the most distinctive groups for classification of water chemistry data (Güler et al., 2002). The enrichment factor (EF) values of the elements in the sediments were calculated using Al as a reference element. Aluminum is widely used for normalization of trace-metal data from marine suspended matter and sediments, because it is a major constituent of fine-grained aluminosilicates with which the bulk of the trace metals are associated (Loring, 1991). EF values were calculated as

EF = ([El]/[Al])sed /([El]/[Al])crust ,

3. Methods

where [El]sed and [Al]sed are the content of the element of interest and Al in the studied sediments, respectively; [El]crust and [Al]crust are the average concentrations of the element of interest and Al in the continental crust (Wedepohl, 1995).

3.1. Sample collection In this study, we used surficial (0–2 cm depth layer) sediment samples collected on KuramBio (R/V «Sonne», 2012), SokhoBio (R/V «Akademik M.A.Lavrentyev», 2015), KuramBio II (R/V «Sonne», 2016) expeditions and Russian-China expedition (R/V «Akademik M.A.Lavrentyev», 2011, 2013) using a multicorer. Table 1 summarizes the coordinates of the sampling sites and the mass percentage of grain size fractions in the sediments.

4. Results The studied sediments consisted of silt and clay mud with minor percentages of a sand fraction (Table 1). Sandy deposits, as well as silt with an admixture of a sandy fraction are located on the slopes of the deep-sea trench and the western part of the Bering Sea. The abyssal plain of the northwestern part of the Pacific and the bottom of the Kuril Basin are composed by the fine dispersed deposits with clay content up to 57%. The difference in the grain composition of the bottom sediments of the investigated area is determined by the geographic area, morphometric parameters and lithodynamic conditions. The spatial distribution of total mercury in surface sediments is plotted in Fig. 1. The Hg concentrations in the study area range from 19 − 158 µg kg−1. The average Hg content in the surface sediments is 88 µg kg−1 in the Kuril Basin (n = 13), 76 µg kg−1 in the KKT (n = 32), and 55 µg kg−1 in the Bering Sea (n = 5) (Table 3). Analysis of the Hg distribution in the surface sediments makes it possible to distinguish high-Hg areas (112 − 158 µg kg−1), such as the Kuril-Kamchatka Trench and the deepest part of the Kuril Basin (Sea of Okhotsk). The organic carbon values vary between 0.84 − 1.92% in the Kuril Basin, and between 0.70 − 1.92% in the Bering Sea. In the KurilKamchatka Trench area, the Corg values range between 0.57 –1.55%, values that are relatively lower than those of the samples collected in the Kuril Basin and Bering Sea (Table 3).

3.2. Laboratory methods The samples were freeze-dried and ground in an agate mill prior to chemical analysis. The mercury concentrations in sediments were determined by mercury Zeeman atomic absorption spectrometer with high frequency modulation of light polarization “RA-915 M” (Lumex Ltd, Russia) and a “PYRO915” pyrolysis attachment without sample pretreatment. The detection limit was 1 µg kg−1 (Sholupov et al., 2004). The sediment Certified Reference Material HISS-1, MESS-4 and PACS-3 from the National Research Council of Canada were used to determine accuracy for Hg analyses. The results of standard sample analyses are presented in Table 2. The organic carbon (Corg) in surface sediments was measured by a “TOC-VCPN” analyzer (Shimadzu, Japan) with an SSM-5000A attachment for the incineration of solid samples. Chemical analysis was performed at the Common Use Center of the Far East Geological Institute, FEB RAS, by ICP-AES using an “ICAP6500 Duo” spectrometer (Thermo Electron Corporation, USA) and by ICP-MS using an “Agilent 7500с” quadrupole mass-spectrometer (Agilent Technologies, USA). Loss on 3

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Table 1 Description of sediment samples and sampling parameters. Station no.

Location Lat N

Water depth (m)

Content (%) of grain fractions, mm

Long E

Kuril Basin Sea of Okhotsk LV55-9 49°31.26' 153.27.14' LV55-41 48°9.49' 147°08.37' LV55-42 46°56.91' 147°12.29' LV55-45 47°18.39' 145°10.36' LV55-48 45°33.14' 144°19.96' LV71-1 46°08.80' 146°00.00' LV71-2 46°41.08' 147°27.99' LV71-3 46°38.00' 148°59.99' LV71-4 47°12.01' 149°36.99' LV71–5 48°37.26' 150°00.32' LV71-6 48°02.96' 150°00.29' LV71-7 46°57.02' 151°05.01' LV71-11 45°36.30' 146°23.10' Kuril-Kamchatka Trench and abyssal plain LV55-4 43°24.74' 147°36.98' LV63-3 50°12.70' 157°28.50' LV63-4 51°37.52' 167°49.77' LV63-5 52°29.09' 165°49.98' LV63-8 53°33.92' 164°27.58' LV63-33 54°20.04' 162°07.18' LV63-40 52°59.22' 160°56.52' LV63-44 52°30.94' 160°16.96' LV71-9 46°16.09' 152°02.10' LV71-10 46°07.87' 152°12.18' So223-1(A1) 43°58.19' 157°19.80' So223-2(A2) 46°14.02' 155°33.10' So223-3(A3) 47°14.26' 154°42.32' So223-4(B1) 46°58.00' 154°32.70' So223-5(B2) 43°34.99' 153°57.96' So223-6(C2) 42°29.00' 153°59.91' So223-7(C1) 43°02.22' 152°59.13' So223-8(D3) 42°14.61' 151°43.51' So223-9(D1) 40°35.01' 150°59.63' So223-11(E1) 40°12.89' 148°06.04' So223-12(E2) 39°43.42' 147°10.01' So250-15(A1) 45°50.88' 153°47.98' So250-95(A2) 44°06.85' 151°25.56' So250-62(A3) 45°10.00' 153°45.43' So250-51(A4) 45°28.75' 153°11.64' So250-39(A5) 45°38.61' 152°55.92' So250-26(A6) 45°55.23' 152°47.47' So250-79(A7) 45°12.94' 152°42.82' So250-4(A8) 43°49.20' 151°45.59' So250-74(A9) 44°39.88' 151°28.11' So250-83(А10) 45°01.36' 151°02.90' So250-101(А11) 44°12.39' 150°36.02' Bering Sea LV63-9 55°23.03' 167°24.91' LV63-12 57°11.05' 169°40.26' LV63-15 59°14.39' 170°46.47' LV63-20 60°23.12' 179°47.22' LV63-23 61°08.95' 176°45.68'

0.063–2.0

0.004–0.063

< 0.004

1937 1639 3354 2426 767 3481 3352 3363 3366 1700 3351 3300 3206

0 0 0 0 0 0 0 0 0 0 2 4 0

78 49 43 78 55 46 53 46 67 71 55 65 44

21 51 57 21 45 54 47 54 33 29 43 31 56

Clayey silt Silty clay Silty clay Clayey silt Clayey silt Silty clay Clayey silt Silty clay Clayey silt Clayey silt Clayey silt Clayey silt Silty clay

2909 1495 2951 3131 3083 1465 2927 1668 3430 4722 5412 4869 4976 5767 5378 5297 5222 5127 5401 5349 5229 8255 6518 5741 8735 7135 6065 9449 5147 8221 5211 9539

1 46 11 21 22 14 34 2 2 0 0 0 1 0 8 1 1 0 0 0 0 0 18 0 0 1 1 0 39 0 25 0

76 37 63 56 52 58 43 62 74 71 68 67 78 57 67 71 77 76 63 67 72 50 49 57 54 64 81 57 36 59 49 51

24 17 26 23 26 28 22 37 24 29 31 33 21 43 25 28 22 24 37 33 28 50 33 43 46 35 18 43 25 41 26 49

Clayey silt Silty sand Clayey silt Clayey silt Sand-silt-clay Clayey silt Sand-silt-clay Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Clayey silt Silt Clayey silt Sand-silt-clay Clayey silt Sand-silt-clay Clayey silt

2560 1888 794 1125 1891

3 0 67 3 3

71 73 20 78 74

26 27 14 20 23

Clayey silt Clayey silt Silty sand Clayey silt Clayey silt

cluster analysis. The results are presented in a dendrogram in Fig. 2. The lithophile elements Al, Fe, Ti, and Mg correlate with the content of the sand fraction and form group I. The basis of this group is one of the main components of detrital clay aluminosilicate sedimentary material, which have high positive correlations amongst one another. The association of Ca-Sr elements associated with biogenic carbonates adjoins this group. Association II includes Si, Cu, Co, Ba, Zr and Y, which correlates with the silt fraction. According to Astakhov (2001), in the sediments of the Kuril-Kamchatka province, Si has a negative correlation with the content of medium- and coarse-grained fractions composed of fragments of medium and basic volcanic rocks enriched in aluminum. Yttrium is associated with heavy resistant minerals, such as zircon, where it enters as an impurity. As shown in Fig. 2, Hg, Corg and the clay fraction form association

Table 2 The results of the determine of mercury in standards of bottom sediments. Standards

HISS-1 PACS-3 MESS-4 a

Sediment type

Content of mercury, µg kg−1 ± Δa Certified

Measured

10 ± 3 3000 ± 500 80 ± 60

9 ± 1.2 3080 ± 280 85 ± 13

– absolute error (µg kg−1), with confidence probability 0.95.

5. Discussion Elemental associations were determined based on processing of the chemical compositional data of the samples for 26 elements using 4

Сorg wt%

Si

Elements

Al

Fe

Kuril Basin Sea of Okhotsk LV55-9 1.38 31.2 3.7 2.4 LV55-41 1.40 30.3 4.5 3.0 LV55-42 1.75 28.1 4.7 3.1 LV55-45 1.67 30.4 4.8 3.0 LV55-48 1.28 29.4 5.3 3.6 LV71-1 1.92 26.9 4.8 3.0 LV71-2 1.56 29.1 5.3 3.5 LV71-3 1.45 29.3 5.0 3.3 LV71-4 1.18 28.0 4.9 3.4 LV71-5 1.34 30.8 3.5 2.4 LV71-6 1.24 27.7 3.5 2.4 LV71-7 0.84 27.5 5.5 4.0 LV71-11 1.83 26.2 4.5 2.9 Average 1.45 28.8 4.6 3.1 Stand.dev. 0.30 1.6 0.7 0.5 Kuril-Kamchatka Trench and abyssal plain LV55-4 1.34 31.1 3.5 2.2 LV63-3 0.79 27.7 8.0 5.4 LV63-4 0.79 22.0 5.0 2.9 LV63-5 0.57 24.9 6.7 3.6 LV63-8 0.57 29.0 7.2 4.0 LV63-33 1.06 27.4 7.5 4.8 LV63-40 1.54 27.7 6.2 3.9 LV63-44 0.93 27.4 7.8 4.9 LV71-9 1.55 28.7 6.2 4.4 LV71-10 0.95 29.0 4.9 3.4 So223-1(A1) 0.81 28.6 5.9 3.3 So223-2(A2) 0.81 28.7 6.0 3.8 So223-3(A3) 1.55 28.3 5.4 3.6 So223-4(B1) 0.98 27.3 7.0 5.0 So223-5(B2) 0.78 28.9 5.8 3.1 So223-6(C2) 0.69 27.7 6.4 3.2 So223-7(C1) 0.44 31.8 6.6 2.5 So223-8(D3) 0.58 30.3 6.4 2.6 So223-9(D1) 1.36 27.1 6.0 3.4 So223-11(E1) 1.45 26.2 5.1 3.1 So223-12(E2) 1.40 28.7 5.2 3.1 So250-15(A1) 1.20 26.3 5.4 3.1 So250-95(A2) 0.80 27.7 6.6 3.9 So250-62(A3) 1.20 27.2 5.6 3.1 So250-51(A4) 1.10 27.7 6.0 3.5 So250-39(A5) 1.10 27.8 6.3 4.2 So250-26(A6) 1.20 28.4 5.0 3.3 So250-79(A7) 1.00 27.7 6.2 3.6 So250-4(A8) 0.30 28.1 7.4 4.0 So250-74(A9) 1.10 28.8 6.1 3.6 So250-83(А10) 1.00 28.5 5.8 3.6 So250-101(А11) 1.10 28.3 5.5 3.0 Average 1.00 28.0 6.1 3.6 Stand.dev. 0.33 1.7 0.9 0.7

Stations no.

1.99 0.75 0.71 0.68 0.75 0.75 0.72 1.01 1.48 1.53 1.14 2.44 0.74 1.13 0.57 2.03 4.32 10.86 7.62 3.53 3.27 2.47 3.88 3.15 1.84 1.38 1.59 1.83 3.07 1.56 1.65 1.67 1.94 0.97 0.94 1.00 1.36 2.02 1.36 1.46 2.39 2.13 1.57 3.44 1.67 2.45 1.29 2.55 2.00

0.10 0.10 0.15 0.23 0.22 0.07 0.06 0.08 0.13 0.25 0.39 0.36 0.15 0.19 0.30 0.32 0.21 0.28 0.95 1.02 0.60 0.33 0.22 0.47 0.54 0.29 0.67 0.30 0.18 0.36 0.15 0.47 0.39 0.35

Ca

0.04 0.50 2.12 0.18 0.06 1.75 0.30 0.25 3.12 0.35 3.87 1.69 2.60 1.29 1.31

Mn

0.73 1.05 1.13 1.19 1.37 1.36 1.33 1.19 0.80 1.00 1.31 1.28 1.09 1.08 1.25 1.40 1.17 1.21 1.63 1.35 1.31 1.31 1.35 1.32 1.37 1.07 0.83 1.41 1.00 1.27 0.93 1.38 1.20 0.20

0.72 1.40 1.56 1.60 1.77 1.54 1.65 1.43 1.11 0.90 0.99 0.89 1.56 1.32 0.35

K

Table 3 The content of the major and trace elements in the surface sediments.

0.99 1.73 1.18 1.44 1.59 2.11 1.86 1.92 1.44 1.35 1.38 1.50 1.58 1.89 1.24 1.28 0.75 0.89 1.39 1.32 1.27 1.50 1.44 1.37 1.46 1.41 1.28 1.49 1.47 1.27 1.35 1.23 1.42 0.28

1.03 1.15 1.21 0.99 1.09 1.31 1.31 1.34 1.27 1.12 1.23 1.41 1.22 1.21 0.13

Mg

0.17 0.43 0.25 0.33 0.38 0.40 0.35 0.42 0.34 0.26 0.26 0.31 0.30 0.42 0.25 0.27 0.19 0.22 0.27 0.24 0.24 0.26 0.32 0.26 0.29 0.35 0.26 0.31 0.34 0.30 0.31 0.26 0.30 0.06

0.18 0.21 0.23 0.24 0.25 0.23 0.24 0.23 0.25 0.17 0.18 0.30 0.22 0.23 0.04

Ti

12.1 3.2 16.0 9.3 4.2 5.4 9.2 4.4 7.2 11.2 10.0 9.3 10.9 6.9 9.5 9.6 5.4 7.1 12.2 16.1 11.8 14.1 9.1 12.7 10.9 8.8 11.0 10.5 5.7 9.6 9.5 11.7 9.5 3.2

11.8 11.8 13.0 11.4 11.4 15.2 11.7 11.7 10.8 12.7 14.4 9.4 16.0 12.4 1.8

LOI

10.7 13.7 16.2 16.2 17.5 23.7 23.5 17.4 12.2 15.8 23.0 24.2 22.0 18.9 21.4 22.6 18.1 18.7 39.8 35.8 28.6 24.5 24.9 27.1 27.1 19.2 14.5 26.3 15.0 25.2 16.4 25.5 21.4 6.4

9.8 27.0 38.6 27.0 31.7 28.9 31.4 26.8 36.2 14.5 48.9 29.6 29.2 29.2 9.8 780 386 2483 1714 1342 435 737 391 646 791 2010 2140 977 767 1950 1890 1090 1210 1910 1440 1440 506 639 944 504 554 608 463 768 482 734 473 1038 607

502 952 635 435 439 635 653 631 642 990 725 486 548 636 174

Li Ba mg kg−1

7.4 14.7 15.1 15.6 16.9 15.5 13.0 15.9 14.8 14.1 20.9 18.8 13.7 17.9 18.1 18.5 8.8 10.7 22.6 24.5 22.0 15.1 16.1 14.7 16.4 16.0 13.1 16.9 14.0 16.8 12.7 16.6 15.9 3.6

8.2 17.0 14.8 9.4 9.3 12.8 11.5 11.5 15.6 14.4 15.1 16.0 11.0 12.8 2.9

Co

35.4 38.1 47.8 58.0 49.4 44.9 52.6 43.8 59.1 85.6 139.8 120.2 90.5 82.2 113.5 114.0 54.7 74.5 194.6 136.8 113.9 102.4 85.2 126.7 101.7 91.2 69.3 95.7 59.5 100.7 76.3 100.7 86.2 35.7

48.4 45.9 56.5 27.2 27.0 46.0 54.1 52.1 53.9 48.6 61.1 55.5 42.0 47.6 10.4

Cu

1.57 1.82 1.94 1.69 1.77 1.83 1.97 1.54 1.33 1.76 4.15 3.91 2.70 2.52 4.05 4.74 3.29 3.65 6.13 4.85 4.79 3.62 3.87 3.80 3.52 2.63 1.63 3.48 2.22 3.39 1.90 3.67 2.99 1.23

1.12 3.83 4.71 3.97 5.07 4.71 5.21 4.39 3.21 1.98 2.44 1.94 4.54 3.63 1.35

Cs

16.7 15.5 34.3 40.8 42.6 41.1 32.1 33.7 27.3 22.0 53.8 60.5 28.0 24.6 41.8 42.4 22.4 38.0 127.0 87.2 59.9 33.2 29.7 48.0 40.5 26.1 20.7 34.3 19.0 29.1 18.6 33.2 38.2 22.1

17.3 46.7 56.0 24.4 27.0 51.1 44.9 45.2 48.8 32.5 59.9 38.4 48.0 41.6 12.8

Ni

1.88 2.11 2.85 2.81 3.49 2.67 2.84 2.30 1.69 3.21 4.30 3.92 2.86 2.82 4.23 4.59 3.74 3.86 5.90 5.09 5.21 4.18 4.86 4.38 4.04 3.21 1.96 3.94 2.87 3.58 2.24 3.75 3.48 1.05

1.22 4.65 5.39 5.82 6.78 5.47 5.51 4.48 3.48 2.15 2.60 2.04 6.45 4.31 1.83

Nb

0.90 1.33 1.20 1.35 1.62 1.34 0.69 2.25 1.11 2.12 2.35 2.79 1.33 1.53 2.02 2.19 2.22 3.71 13.6 17.5 8.50 3.72 2.03 5.46 10.4 2.95 9.61 3.08 1.34 4.29 1.20 7.76 3.86 4.02

0.79 4.16 41.7 1.36 0.94 11.3 1.76 1.23 43.7 2.42 37.6 29.2 30.6 15.9 17.6

Mo

12.4 6.7 12.8 10.5 10.2 7.3 8.0 6.9 9.5 12.3 25.2 22.6 13.8 14.1 24.0 26.9 19.8 20.4 34.6 27.9 27.3 19.2 18.2 21.6 18.4 15.1 12.0 18.9 12.8 19.1 13.4 20.0 16.9 7.0

9.7 23.1 22.5 16.5 20.5 22.5 18.7 20.7 16.3 16.1 16.0 14.6 25.1 18.6 4.3

Pb

20.9 27.3 30.0 29.4 33.7 31.8 33.2 26.9 19.1 25.9 51.3 60.5 36.5 34.5 47.4 55.0 36.5 39.0 74.2 60.9 59.9 45.1 55.1 47.2 46.5 33.7 22.3 47.4 30.5 43.7 26.1 47.7 39.7 13.2

17.4 58.7 70.6 69.8 83.0 68.2 73.4 59.5 44.4 28.5 34.3 26.1 66.6 53.9 21.2

Rb

1.68 1.47 2.21 2.11 2.35 1.78 1.92 1.43 1.42 1.90 4.44 4.32 2.76 2.74 4.41 5.05 3.73 3.87 6.80 5.39 5.37 4.14 4.71 4.37 3.93 2.90 1.88 3.89 2.76 3.74 2.15 4.03 3.30 1.40

1.32 4.76 5.64 5.59 6.57 4.84 4.87 4.10 2.99 1.97 2.39 1.75 5.82 4.05 1.76

Th

0.98 0.73 0.82 0.77 0.88 0.88 1.13 0.78 0.69 0.99 1.28 1.39 1.32 1.09 1.32 1.30 1.21 1.26 1.75 1.68 1.69 1.27 1.31 1.29 1.36 1.00 0.98 1.19 0.83 1.16 0.88 1.28 1.14 0.28

0.99 1.31 1.57 1.46 1.59 1.33 1.22 1.06 1.35 0.86 1.42 0.82 2.16 1.32 0.36

U

175 339 566 451 333 303 264 331 262 208 239 259 231 295 247 245 239 236 206 192 188 173 213 184 183 210 202 191 277 183 221 167 250 84

215 185 201 186 187 201 160 167 207 195 208 244 208 197 21

Sr

12.6 19.3 15.9 17.7 17.7 16.2 14.3 17.3 16.7 13.6 16.8 17.9 14.7 17.3 18.2 21.3 24.5 22.3 15.7 14.3 14.1 14.1 17.4 15.0 14.7 16.8 13.9 15.0 19.1 16.5 16.4 14.4 16.6 2.6

10.1 10.8 12.9 11.3 13.1 12.5 12.7 13.2 14.6 9.3 10.8 18.7 12.3 12.5 2.4

Y

66.7 94.8 74.9 86.7 93.4 95.0 103 96.2 78.9 76.2 86.3 99.7 83.7 88.2 79.4 80.5 73.1 73.8 121 117 93.6 75.3 85.8 86.7 87.7 87.2 75.7 84.0 74.9 84.8 81.8 76.8 86.3 12.1

39.0 52.8 59.6 53.1 63.0 54.1 57.4 53.9 49.9 38.1 41.9 52.30 55.33 51.6 7.6

Zr

57 84 84 44 48 130 107 105 109 82 108 79 112 88 27

Hg µg kg−1

43.4 42 68.4 20 66.4 79 84.5 44 92.2 44 69.7 58 67.1 60 68.9 30 56.1 54 53.4 89 87.0 92 92.2 127 71.0 143 73.6 124 96.0 86 101.0 74 119.0 46 110.0 54 94.6 72 76.2 116 79.0 93 73.8 69 81.4 58 76.4 40 76.0 47 70.6 93 51.4 65 75.6 122 76.7 19 73.7 158 59.2 66 71.7 147 76.8 76 16.3 37 (continued on next page)

53.8 125 113 68.9 74.7 109 119 120 106 88.9 103 94.9 95.9 97.80 21.45

Zn

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53 110 24 33 53 55 33 62.8 67.5 59.6 57.2 54.8 60.4 5.0 97.5 133 73.5 99.3 98.7 100 21.2 10.9 13.4 13.9 14.2 13.2 13.1 1.3 307 230 291 225 229 256 39 1.03 1.62 1.11 1.78 1.83 1.47 0.38 1.68 3.81 3.44 5.06 5.09 3.82 1.40 28.4 52.3 55.2 56.7 58.9 50.3 12.5 6.2 9.2 8.3 10.4 9.6 8.7 1.6

III, which was extracted by cluster analysis, and can be explained by the concentration of mercury with natural organic material forming strong complexes. These results are in good agreement with studies which showed that Hg concentrations in marine sediments correlated well with Corg content (Hammerschmidt et al., 2004; Hammerschmidt and Fitzgerald, 2004; Liu et al., 2017; Pempkowiak et al., 1998; Shi et al., 2005; Sunderland et al., 2009) and varied inversely with sediment grain size (Covelli et al., 2001; Liu et al., 2017; Pempkowiak et al., 1998). The greatest methylation in the oceanic water column occurs in the thermocline zone, as a result of which it becomes more bioavailable and concentrated in phyto- and zooplankton (Gosnell and Mason, 2015; Sunderland et al., 2009; Xia et al., 1999). Associated with the clay fraction are many rare elements that are part of authigenic and biogenic components. LOI is characterized by a stable positive correlation with the clay fraction content. This indicates that the main variation in this indicator is determined by the water in clay minerals. The remaining volatile components either constitute a negligible part (as Corg) or are distributed in other fractions relatively evenly. According to Astakhov et al. (2007), the correlation between mercury and the content of organic matter has been demonstrated, and is considered to be an indication of the prevailing atmospheric release of mercury into the basin. Mercury concentrations in marine surface sediments can vary widely. The enrichment factor concept is often used to assess the metal contamination status of the marine environment. The calculated EF at each sampling station is shown in Fig. 3. The EF values at the stations range between 0.3 − 4.3. An EF value of 1 indicates a predominantly natural origin for the element in the sediment, while values greater than 1.5 indicate enrichment by either natural processes (e.g., contributions from biota) or anthropogenic processes (Zhang and Liu, 2002). According to Wedepohl (1995), the average concentration of mercury in the upper layer of the Earth's crust is 56 µg kg−1 Hg. By way of referencing the natural background, we can use the average concentration of mercury in the layers of bottom sediment accumulated in the preindustrial period. Baseline concentrations for shelf sediments are in the range of 20–70 µg kg−1 Hg (Aksentov and Astakhov, 2009; Polyakov et al., 2008; Sanders et al., 2006; Tomiyasu et al., 2014). Consider the level of mercury concentration in bottom sediments from the anomalous anthropogenic and natural zones. Direct discharge of mercury-containing wastes occurred in Minamata Bay, Japan, as a result of which, the bottom sediments accumulated a significant amount of mercury. The concentration of mercury reaches 4300 µg kg−1 Hg in the contaminated layers (Tomiyasu et al., 2014). In places with anthropogenic pollution, but without specificity with respect to character of mercury-containing waste, for example, the

1.69 1.92 0.70 1.65 1.76 1.54 0.48

29.8 29.7 31.8 31.6 31.6 30.9 1.1

5.8 5.4 6.5 5.6 5.3 5.7 0.5

3.2 3.2 3.5 3.0 2.9 3.1 0.2

0.04 0.04 0.04 0.04 0.03 0.04 0.01

2.23 1.72 1.91 2.00 1.92 1.96 0.19

1.16 1.42 1.76 1.54 1.52 1.48 0.22

1.60 1.39 1.16 1.29 1.26 1.34 0.17

0.28 0.29 0.33 0.33 0.31 0.31 0.02

7.9 9.7 3.6 6.4 7.2 7.0 2.2

19.3 28.4 24.4 23.3 24.7 24.0 3.2

1079 1463 572 734 869 944 345

10.4 9.4 8.7 9.1 8.7 9.2 0.6

47.1 56.2 20.7 27.1 31.0 36.4 14.8

1.57 3.38 2.55 2.75 3.00 2.65 0.68

28.9 34.7 50.1 29.5 29.9 34.6 9.0

2.55 5.05 5.22 6.72 6.55 5.22 1.67

0.85 0.92 1.43 0.89 0.84 0.99 0.25

Th Rb Si Сorg wt%

Fig. 2. R-mode dendrogram of cluster analysis of sediment samples.

Bering Sea LV63-9 LV63-12 LV63-15 LV63-20 LV63-23 Average Stand.dev.

Stations no.

Table 3 (continued)

Elements

Al

Fe

Mn

Ca

K

Mg

Ti

LOI

Li Ba mg kg−1

Co

Cu

Cs

Ni

Nb

Mo

Pb

U

Sr

Y

Zn

Zr

Hg µg kg−1

V.V. Sattarova, K.I. Aksentov

6

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V.V. Sattarova, K.I. Aksentov

Fig. 3. Enrichment factors for mercury in surface sediments.

concentration is at the level of global bulk values for the upper crust and the background for the shelf. Our studies have shown that hydrothermal sources (endogenous) on the Piip Volcano exert a local influence on the distribution and accumulation of mercury in sediments in the study area.

Zolotoy Rog Bay (near Vladivostok, Russia), the mercury content is in the range 700–1500 µg kg−1 Hg (Aksentov and Astakhov, 2009; Polyakov et al., 2008). The concentrations of total Hg in the Anadyr Estuary in the Bering Sea vary between 77–112 µg kg−1 Hg, and are thus low, except for one sample which contained 2100 µg kg−1 Hg (Kannan and Falandysz, 1998). Accumulation of mercury in bottom sediments can also take place from geological sources. In the sediments of the Sea of Okhotsk, the background value for mercury is 11 µg kg−1 (Astakhov et al., 2007). At the same time, in the Deryugin Basin of the Sea of Okhotsk, the mercury concentrations in sediments from near hydrothermal Barite Mountains vary between 400–900 µg kg−1 Hg (Astakhov et al., 2007). However, in the bottom sediments from the slopes of the underwater Piip Volcano in the Bering Sea, where the hydrothermal activity takes place, the mercury content is relatively low at 20–57 µg kg−1 Hg, with an average of 37 µg kg−1 Hg (Astakhov et al., 2011). Our study also confirms this, since the concentration of mercury at station LV63-9 was found to be 53 µg kg−1 Hg (see Tables 1, 3). The Canadian interim sediment quality guideline (ISQG) is 130 µg kg−1 Hg, although other guidelines include the level above which adverse effects are expected as the ‘probable effect level’ (PEL, 700 µg kg−1 Hg) (CME, 2001). In addition, guideline values exist as an ‘effects range-low’ (ERL, 150 µg kg−1 Hg) and an ‘effects range-median’ (ERM, 710 µg kg−1 Hg) (Long et al., 1995). These guidelines for Hg can be used to evaluate the degree to which adverse biological effects are likely to occur in aquatic biota as a result of exposure to Hg in sediments. The maximum concentration in the samples is 158 µg kg−1 Hg, while the upper quantile was 107 µg kg−1 Hg. These values approach the ISQG and ERL, but are lower than the PEL and ERM. Comparing these data, we can assume a minimal toxic mercury effect on the benthic marine biota (benthos).

Acknowledgments The authors are extremely grateful to Dr. M. Malyutina, Prof. Dr. A. Brandt, Prof. X. Shi and Dr. S.A. Gorbarenko for an invitation to join the expedition. Special thanks go to the Laboratory of Analytical Chemistry at the Far East Geological Institute for help with chemical analyses. Thanks are due to the Captain and crew of the RV Akademik M.A. Lavrentyev and RV Sonne for their help with the sampling. We are also very grateful to anonymous reviewers of our manuscript for their valuable comments and suggestions, which greatly improved this document. The work was supported by the National Natural Science Foundation of China (U160641, 41420104005), by the Russian Science Foundation (Project no. 14–50-00034), by the Russian Foundation for Basic Research (Grant no. 16-04-01431-а) and by the Far Eastern Branch of the Russian Academy of Sciences (Grant no. 15-I-1-005o). This is a SokhoBio publication # 3. References Aksentov, K.I., Astakhov, A.S., 2009. Anthropogenic pollution of bottom sediments by mercury in Peter the Great Bay. Vestn. DVO RAN 4, 115–121. Arseniev,V., Leontieva,V., 1970. Water masses of the southern part of the Kuril–Kamchatka Trench in the summer of 1966. In: Bogorov, V.G. (Ed.), Fauna of the Kurile–Kamtschatka Trench and its environment. Moscow, 10–29 in (Russian). Astakhov, A.S., 2001. Lithochemistry of Bottom Sediments of East Asian Marginal Seas. Dalnauka, Vladivostok, pp. 240 (in Russian). Astakhov, A.S., Ivanov, M.V., Li, B.Y., 2011. Hydrochemical and atmochemical mercury dispersion zones over hydrothermal vents of the submarine Piip Volcano in the Bering Sea. Oceanology 51, 826–835. Astakhov, A.S., Wallmann, K., Ivanov, M.V., Kolesov, G.M., Sattarova, V.V., 2007. Distribution and accumulation rate of Hg in the upper quaternary sediments of the Deryugin Basin, Sea of Okhotsk. Geochem. Int. 45, 47–61. Baranov, B.V., Werner, R., Hoernle, K.A., Tsoy, I.B., van den Bogaard, P., Tararin, I.A., 2002. Evidence for compressionally induced high subsidence rates in the Kurile Basin (Sea of Okhotsk). Tectonophysics 350, 63–97. Covelli, S., Faganeli, J., Horvat, M., Brambati, A., 2001. Mercury contamination of coastal sediments as the result of longterm cinnabar mining activity (Gulf of Trieste, northern Adriatic sea). Appl. Geochem. 16, 541–558. Dastoor, A.P., Larocque, Y., 2004. Global circulation of atmospheric mercury: a modelling study. Atmos. Environ. 38, 147–161. Fitzgerald, W.F., Lamborg, C.H., Hammerschmidt, C.R., 2007. Marine biogeochemical cycling of mercury. Chem. Rev. 107, 641–662. Gnibidenko, H.S., Hilde, T.W.C., Gretskaya, E.V., Andreev, A.A., 1995. Kurile (South Okhotsk) back-arc basin. In: Taylor, B. (Ed.), Back-Arc Basins: Tectonics and Magmatism. Plenum Press, New York, pp. 421–449.

6. Conclusions The results of this study demonstrate that the range of total mercury concentrations in surface sediments is 19–158 µg kg−1 Hg, with mean of 77 µg kg−1 Hg (n = 50). The maximum content of mercury is confined to deep-water clay sediments collected in the Kuril Basin, in the Kuril-Kamchatka Trench and on its slopes, whereas the minimum concentrations are recorded in sandy sediments. According to the correlation and cluster analyses, an association consisting of mercury, clay fraction, LOI and Corg is distinguished. Consequently, it is interpreted that mercury in the open ocean accumulates in bottom sediments due to biogenic precipitation. Compared to abnormal zones, both anthropogenic and natural, the mercury content in the sediments is low. At the same time, the average 7

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