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Concentrations of heavy metals in live and dead leaves, stems, rhizomes and roots of the seagrass Zostera marina Linnaeus, 1753 are analyzed in the study. On the basis of the concentration, the metals are arranged in the following order: Fe > Mn > Zn > Cu > Pb > Ni >Cd. Differences in Fe, Pb, Ni, and Cd for live and dead leaves are revealed. The factor of sediment enrichment in heavy metals from dead leaves is calculated. The enrichment factor for the studied metals changed in the order Cu > Pb > Zn > Ni > Mn, and the value of solubility product [–log(SP)] for sulfides of the above-listed metals changed in the same order. [ABSTRACT FROM AUTHOR]

The content of 237Np, 239,240Pu, and 241Am in seawater, suspended matter, and bottom sediment cores of the Ussuri and Amur Bays, sampled in July 2021 and August 2022, was analyzed. The activity concentrations of 237Np, 239,240Pu, and 241Am in the water of Peter the Great Bay were determined for the first time and were found to be equal to (19–105) × 10–3, 2.0–5.3, and 24.1–33.5 mBq/m3, respectively. The activity concentrations as well as the 239Pu/240Pu isotope ratio (⁓0.18) in the bottom sediments definitely indicate that global fallout is the main source of plutonium in the investigated territory. The sedimentation rates were determined for the Amur Bay (in the Razdolnaya River estuary), 0.9 mm/year, and for the Ussuri Bay, 4.1 mm/year. Actinide transfer coefficients were determined for Peter the Great Bay in the system dissolved forms (including colloids)–suspended matter–bottom sediment. [ABSTRACT FROM AUTHOR]

Comprehensive study of the lagoon terrace section at the apex of Amur Bay has made it possible to identify sharp short-term cooling events at 4450, 2870–2510, 1740–1200, and 680–150 cal BP that are compared to cold events in many regions around the world. The reconstructions are based on the results of diatom, botanical, and palynological analyses. The age–depth model is generated by the Bacon program using radiocarbon dating and tephrostratigraphy. Tephra B-Tm from the caldera-forming eruption of Baitoushan volcano was found in the section. The section selected as a natural archive has its own specifics. In contrast to the mountainous areas and river basins, where the climate became dry 3320–3050 years ago due to a sharp decrease in the intensity of the summer monsoon, coastal lacustrine–boggy sequences developed in constantly waterlogged conditions. This made it possible to identify short-term dry events that correlate well with the global climatic rhythm caused by the decrease in solar radiation. The decrease in moisture was closely related to the influence of the ocean: the intensity of tropical cyclogenesis. The shallowing of the lagoon during the decline of the low-amplitude transgression, intensified by the weakening of the summer monsoon, led to a change from terrigenous to organogenic sedimentation at about 3460 years ago. The cooling event 2870–2510 years ago had the most complex structure with sharp changes in moisture. Change in the course of bog-forming processes around 1740 years ago associated with the activation of floods, which caused periodic flooding of the peat deposits in the vast estuary zone of the Razdolnaya River, led to the disappearance of the tree layer and the development of a grass bog. In general, the regional conditions were dry until the Medieval Warm Period. The response of the landscapes to cooling is identified: the role of broadleaved species in the forest vegetation of the low mountains decreased, and the participation of plants preferring less inundated habitats in the development of local landscapes increased. The Little Ice Age is the exception of the cold events, which was wet and characterized by frequent floods. The meridional transport of moist air masses from the ocean to the continent became more active during that time. [ABSTRACT FROM AUTHOR]

Size and sex structure of estuarine-freshwater mysid Neomysis awatschensis in the northern Amur Bay is considered, time of their aggregations formation is determined, and their biomass is estimated on the data of surveys conducted in 2014–2019. The samples were collected at the depth of 0.5–2.0 m in the daytime in May-July. The catches were recalculated per 1 m3 of water. All collected mysids (2212 ind.) were measured under binocular microscope with accuracy of 0.1 mm, weighted by torsion scales with accuracy of 1 mg, and separated to males, females and juveniles. The females were differentiated by 5 stages of their development: 1) immature females with oostegetic rudiments; 2) oviparous females; 3) females with embryos in the marsupia bags without stalk-eyes with black pigment; 4) females with embryos in marsupia bags with black eyes; 5) spawned females with empty marsupii. Time and duration of N. awatschensis aggregating changed by years in dependence on hydrological and weather conditions; the aggregations were either monospecific or mixed with another mysid species — N. mirabilis. The maximum mysid biomass could exceed 500 g/m3 that was appropriate for commercial fishery. The maximum body length of mysid females was 13.7 mm, of males — 12.0 mm. The average length varied from 6.7 to 10.3 mm, being shorter in summer months than in May. Portion of males in the aggregations was always significant (16.3–50.7 %), portion of females varied from 8.7 to 52.5 %, portion of juveniles was the largest in June (29.9–75.0 %). The females to males ratio was 1 : 1 in May and July of 2014–2017, but males prevailed in June 2015 (1.0 : 1.9), whereas females prevailed in June 2016 (1.8 : 1.0). Spawning of the mysids was the most intensive in May-June, though females had embryos at different stages of development in all samples that indicated an extended period of reproduction.

Data on dissolved organic concentration (DOC) and concentration of nutrients (phosphorus, silicon, and nitrogen of ammonium, nitrite and nitrate) in the Razdolnaya/Suifen River water are presented. The samples were collected fortnightly, as a rule, during more than a year (2013–2014). The nutrients concentration decreased and DOC and humic substances concentration increased with the river run-off increasing. In conditions of monsoon climate, the nutrients discharge from the Razdolnaya/Suifen into the Amur Bay had great pulsations that promoted sometimes producing of «excessive» phytoplankton biomass in the bay and provided a background for hypoxia at the bottom. Natural terrestrial fluxes of nutrients and DOC into the bay are much higher than these substances supply with waste waters of Vladivostok City. Interannual variability of the nutrients and dissolved organics fluxes into the Amur Bay is traced. Tendency to their increasing is supposed since 2003 because of the Razdolnaya/Suifen River annual discharge increasing observed by Hydrometeorological Agency in 2003–2017.

Size and sex structure of mysid Neomysis mirabilis in Peter the Great Bay is studied. The net samples (160 and 260 per year) were collected at the depth of 0.5–2.0 m in the southern external part of the secondary Amur Bay (at Popov and Reineke Islands) and in its northern internal part, over the total area of approximately 3 km2 , in the daytime in May-September from 2014 to 2017. The catch was recalculated per 1 m3 of water. The water temperature was measured and weather conditions were recorded. All mysids (2926 ind.) were measured under binocular microscope with accuracy of 0.1 mm, weighted by torsion scales with accuracy of 1 mg, and separated to males, females and juveniles. The females were differentiated by 5 stages of development: 1) immature females with oostegetic rudiments, 2) oviparous females, 3) females with embryos in the marsupia bags without stalk-eyed with black pigment, 4) females with embryos in marsupia bags with black eyes, 5) spawned females with empty marsupii. The females prevailed: 71.3–97.0 % in the southern Amur Bay and 39.0–56.7 % in the northern Amur Bay, while the portion of males was 2.2–28.7 % and 20.9–43.3 %, accordingly. The body length varied from 3.0 to 23.5 mm; the females and males had the same sizes, on average 14.5–15.4 mm in the southern Amur Bay and 8.3–11.2 mm in the northern Amur Bay, with slight decreasing from spring to summer. The spawning was extended in time because of several generations changing. Mysid females with eggs, their embryos at different stages of development, and juveniles of different size were presented permanently. Aggregations of N. mirabilis formed for a short time starting in middle April — middle July in the southern Amur Bay and in middle May — late July in the northern Amur Bay. The mysid biomass in the aggregations was 3–5 g/m2 and 10–500 g/m2 in these areas, respectively, that is appropriate for the commercial fishery. Spatial difference of the mysid biological parameters and abundance is explained by different environmental conditions in the internal and external areas of the Amur Bay.

This paper presents the results of study of diatoms in each centimeter of sediments in cores A12-4 and A12-5 from Amur Bay (Sea of Japan) that have formed over the last 150 years. Diatom algae show significant changes in the quantitative content and ecological structure of the assemblages, which reveal the conditions of sediments accumulation. The study showed that in lithologically homogeneous sediments, with relatively high sedimentation rates and the absence of bioturbation, sharp short-term diatoms concentration declines coincide with the minimum bromine content associated with extreme floods caused by typhoons, which can be used in paleoreconstructions. The results confirm the data on the increase in the intensity and frequency of typhoons over the past 60 years in the study area due to global warming.

Quantitative samples of fish, crabs and shrimps from the Razdolnaya estuary are analyzed. The area surveyed in May-September of 1990–2014 includes the internal estuary of this largest river of southern Primorye and its external estuary — the top of the Amur Bay with the depth < 13 m. In total, 478 samples were collected: 244 in the external estuary by trawl and 234 in the internal estuary by fry seine. Distribution density and biomass are calculated using the «areal» method with certain coefficients of catchability (1.0 for fry seine). The upper freshwater layer (salinity 0–5 ‰) was observed in the lower stream of the river till sandy bar, the brackish-water cline was traced at the river bottom from the mouth to the distance 10–15 km upstream. The seawater with salinity > 30 ‰ did not penetrate over sand bar to the river. Species diversity of fish and decapods was presented by 108 taxa (fishes — 88, decapods — 20) belonged to 43 families, among them 84 species were caught in the Amur Bay and 41 species in the Razdolnaya, but no more than 67 species were caught in the Amur Bay only and 24 species — in the Razdolnaya only, other 17 species were found in both external and internal estuaries (Acanthogobius flavimanus, Acanthogobius lactipes, Crangon septemspinosa, Crangon spp., Eriocheir japonica, Hypomesus nipponensis, Giporhamphus sajori, Konosirus punctatus, Liopsetta pinnifasciata, Oncorhynchus masou masou, Palaemon sp., Pholis nebulosa, Planiliza haematocheila, Pugettia quadridens, Salangichthys microdon, Syngnathus schlegeli and Tribolodon spp.). Total biomass was higher (9.1 g/m2 ) in the external estuary than in the internal estuary (6.7 g/m2 ) with the mean value 9.0 g/m2 . It was almost uniform over the internal estuary with only slight increasing on the distance about 5 km from the mouth. Simpson index of dominance increases from external to internal estuary but decreases in the river in the order: 0.127 at Peschany Peninsula — 0.168 in the northwestern Amur Bay — from 0.193 to 0.252 in the internal estuary — 0.164 in the river. Six clusters with similar species composition are defined, they change in direction from the sea to the river in the following order of the dominant species: L. pinnifasciata in the sea — prawns gen. Palaemon at the bar (upper part of the external estuary) — P. haematocheila at the river mouth (lower part of the internal estuary) — P. haematocheila and E. japonica in the main part of the internal estuary — Acanthorhodeus chankaensis and Gobio macrocephalus (with the highest biomass up to 22 g/m2 ) in the minor adjoining river stream — G. macrocephalus in the upper part of the internal estuary.

Seasonal changes of chlorophyll a profiles are traced over the Amur Bay (Peter the Great Bay, Japan Sea) in May-October, 2017 by means of oceanographic sonde-profiler equipped with fluorometer. Two principally different types of the vertical profiles are revealed, which were formed by different mechanisms of productivity: i) Chl a concentration had the maximum at the sea surface and decreased with the depth in the internal part of the bay occupied by the estuarine waters, and ii) Chl a concentration had the maximum below the seasonal pycnocline in the external part of the bay connected with the open sea. The highest Chl a concentration was observed in July-August for the estuarine type because of summer monsoon flood on the rivers, but in September for the marine type because of the coastal upwelling induced by monsoon winds change. Comparing these results with estimations of Chl a concentration made with the satellite data, insufficient correspondence is concluded for the external part of the bay, outside the estuarine zone, because the satellite data don’t reflect well the chlorophyll a in the subsurface layer and its seasonal variations. Thus, underestimation of real productivity and feeding ability of marine areas is available with the satellite data on chlorophyll a.

The water dynamics and distribution of the sea grass Zostera marina are investigated as factors of the curative mud forming in the Voevoda Bay. The water currents are measured directly. The closed circulation is formed in the middle part of the bay by prevailing winds: anticyclonic by northwestern wind and cyclonic by southeastern wind. Zostera marina distribution is researched by divers. Its highest biomass is observed on the shallows where projective coating is 100 % and mean biomass is 3 kg/m2 (wet weight). Bottom sediments and depth of the acoustic basement are mapped using seismoacoustic method. The maximal thickness of the curative mud layer is found in the internal part of the bay (Melkovodnaya Bight) where it reaches 15 meters.

The history of coastal catastrophic floods was reconstructed for the first time using the geochemical proxy in shelf sediments. The reconstruction is based on the identification of sediment layers accumulated on the shelf during the intensive discharge of the river runoff suspended matter from the land which does not contain bromine. The set of isotopic (AMS 14C, 210Pb, 137Cs), tephrastratigraphic, and paleomagnetic methods was used for the detailed chronology of sediments. The scanning of chemical composition of sediments with the step of 0.5–0.8 mm is performed using the synchrotron radiation X-ray fluorescence in the VEPP-3 storage of the Institute of Nuclear Physics of Siberian Branch of Russian Academy of Sciences. The history of catastrophic floods for the past 1800 years is reconstructed based on the typical variations in bromine concentration in one of the cores from the Amur Bay (the Sea of Japan). New methodological approaches to the flood signal extraction are proposed. The revealed inverse correlation between the frequency of floods caused by typhoons over the coast of the Sea of Japan and southern China agrees with the existing assumption on the change in their trajectories in different periods of global climate change. [ABSTRACT FROM AUTHOR]

Water pollution by heavy metals in Uglovoi Bay in 2015–2016 was analyzed. The concentrations of Mn, Fe, Cu, Ni, Hg, As, Pb, Cd, and oil products were found to exceed the corresponding MAC values. The development of hypoxia and the accumulation of dissolved heavy metals were taking place at the northeastern coast of the bay. River runoff was concluded to be the main source of pollutant inputs into bay water. Studies of ice core samples showed the accumulation of large amounts of heavy metals. Ice cover accumulates pollutants and initiates the processes of their input into water. The pollution of water in Uglovoi Bay by heavy metals and oil products in 2010–2016 is evaluated. [ABSTRACT FROM AUTHOR]

Chemical and ecological state of the Novik Bay waters is described on the data of surveys conducted in summer, autumn, winter, and spring of 2014-2015. Lowered content of dissolved oxygen is noted for summer, with occasional decreasing to 5-6 mg/L that is below the standard summer value for fishery ponds. However, the oxygen content restores quickly in autumn, up to 12 mg/L, that is conditioned by hydrodynamic activity, water temperature decreasing, and phytoplankton blooming. The latter process is confirmed by high values of BOD5 (4.44-5.58 mgO2/L) in autumn. Winter conditions under the sea ice are satisfactory for marine organisms: dissolved oxygen content is > 4 mg/L in the whole water column that is close to the standard winter value for fishery ponds.

Results of long-term studies of zooplankton species in the Amur Bay (Japan Sea) are analyzed. Two seasonal «waves» of the allochtonous species are defined: the first in the early summer that is formed mainly by inter-zonal copepods spawning in the deep layers ( Metridia pacifica , Neocalanus plumchrus, Calanus glacialis ) and the second in the late summer that is represented by warm-water copepods of subtropical origin ( Calanus pacificus and Paracalanus parvus ) obviously transported from the southern Japan Sea by currents. The latter species is able to dominate in the zooplankton community of coastal waters in the early-autumn season. Variations of this mass species abundance in the Amur Bay under changes of wind-driven upwelling/downwelling circulation are investigated using an empirical advective model of its cross-shelf transport. There is found that strong summer southern on-shore winds (summer monsoon) are favourable for its high abundance but in these conditions it is transported toward the coast by the deep compensatory flow developed only after the summer monsoon change to the winter monsoon with opposite direction; that’s why the high abundance is observed in autumn, in September-October. In the years with weak summer monsoon the species is transported to the bay in mass by the surface on-shore wind-driven flow earlier, in August, but its number decreases after the monsoon change, so the maximum of abundance is not high. Patterns of the transport by cross-shelf currents depend supposedly on the depth of plankton concentration. Recent strengthening of summer monsoon causes heightening of P. parvus abundance in the coastal waters at southern Primorye, up to extreme high values in 2013, but climatic trend of the summer monsoon intensity is negative, so decreasing of this species transport toward Primorye coast and its abundance in the coastal waters, as the Amur Bay, can be expected in the nearest future.

Downwelling/upwelling influence on hypoxia at the bottom of the Amur Bay is determined on the data of oceanographic surveys conducted aboard RV Impulse in August 2012 and RV Malachite in August 2013 coupled with the data of monitoring oceanographic station in the bay. The hypoxia develops in the period of downwelling circulation driven by southern and southeastern winds and relaxes in conditions of upwelling induced by northern and northwestern winds.

Recent climate-scale (> 3 decades) changes of water temperature, salinity, and concentration of inorganic phosphorus, silicon and nitrogen (nitrites and nitrates) are considered for the Amur Bay where Vladivostok is located ashore. Mean seasonal values of these parameters are determined for the 1980s and 2000s. In summer, the tendencies of climatic scale are noted of SST heightening, temperature at the sea bottom lowering, and nutrients depletion in the upper layer, except of nitrate. In general, the bay becomes more stratified and less productive, on the primary trophic level, but the nitrate income, presumably from atmosphere, prevents the productivity decreasing. Links of the changes with external conditions are analyzed, and the summer monsoon weakening is defined as their main reason that determines weather conditions over Primorye and cross-shelf exchange on its shelf. These processes related with the summer monsoon present the mechanism of large-scale climate changes downscaling to meso-scale level. Besides, there is concluded that the Amur Bay is more vulnerable to marine processes than to terrestrial ones, though it is subjected to the large river discharge.

Mercury levels in the abiotic components of the Razdol'naya River-Amur Bay geosystem are determined. The obtained mercury concentrations correspond to modern global values. Mercury accumulated in the deposit environments is transported to the bay during floods and creates a local geochemical background. The migration of mercury is carried out in the form of suspended matter and single fragments of soil cover which can be deposited in the open parts of the Peter the Great Gulf shelf according to the existing circulation of surface waters. [ABSTRACT FROM AUTHOR]

The distribution of REE in the bottom sediments of Amur Bay accumulated over the last 100 years was studied, and the REE contents were evaluated. The REE contents normalized to North American Shale Composite (NASC) show a negative Ce anomaly and a predominance of LREE and MREE. The inflow and accumulation of REE in the bottom sediments are influenced mainly by natural sources, whereas their dependence on anthropogenic factors is minimal. [ABSTRACT FROM AUTHOR]

X-ray fluorescence scanning with synchrotron radiation was performed to study sediment core records of floods in Amur Bay, Sea of Japan. Interlayers of 3-8 mm with abnormally low bromine content were formed by the Razdolnaya River discharge to the central part of the bay during extreme floods, accompanied by severe storms at sea. Such conditions in the region are typical for periods of deep tropical cyclones (typhoons), to which the distinguished interlayers were compared on the timescale. This approach was made possible thanks to the high rate of sedimentation in the bay (3-5 mm/a) and low bioturbation of sediments under anoxic conditions. [ABSTRACT FROM AUTHOR]

Siliceous unicellular microalgae - diatoms and silicoflagellates from sediments in Amur Bay were analyzed with high temporal resolution to examine changes over the last 150 years. The age of sediments was estimated from unsupported Pb controlled by Cs. Siliceous microalgae examined in each cm of two sediment cores demonstrated significant changes in the ecological structure of the assemblages that reflected changes in sedimentation conditions. During the years 1860-1910 the sediments accumulated under the great influence of river runoff. For about the next 50 years the number of freshwater species and marine benthic diatoms in sediments sharply declined, which is probably connected with the weakening of the effects of river runoff due to deforestation. Since the early 1960s the sedimentation conditions in the Amur Bay changed significantly. Marine planktonic diatoms and silicoflagellates began to prevail in sediments and this reflects increasing microphytoplankton productivity. One consequence of this was the formation of seasonal bottom hypoxia in Amur Bay. The ecological structure of diatom and silicoflagellate assemblages indicates that the sea level began to rise since the early 1960s and this corresponds to the water and air temperature increase in the area for that period. The obtained data suggest that the environmental changes over the last 150 years in Armur Bay are associated with the weakening of river runoff due to deforestation, sea level rise caused by global warming, and the increase of siliceous microplankton productivity that resulted in the formation of seasonal bottom hypoxia. [ABSTRACT FROM AUTHOR]

The article presents a case study of geochemical indicators for creation of typhoons in shelf sediments of Amur Bay of the Sea of Japan. It reports that sedimentary material brought by the Razdol'naya River acts as an indicator of paleo-typhoon. It highlights favorable factors for paleo-typhoon including low bioturbation of sediments due to ill treatment of benthic fauna and anoxic conditions of sedimentations.

Data on Amur Bay (the Sea of Japan) are used to show the existence of a dependence between the diurnal variability and the mean daily concentrations of various hydrochemical characteristics, which can be approximated by power function. The formation mechanism of such dependences is considered. Relationships between the parameters of such functions and variability of water salinity are obtained. The possible variation limits of such parameters in a coastal tidal zone of a sea, subject to the effect of coastal runoff. In the frontal mouth zone, one of the parameter (the exponent) linearly increases toward the river, thus reflecting the increase in the contribution of water dynamics to the diurnal variability of characteristics. The notion of variability of characteristics 'by salinity' is introduced. [ABSTRACT FROM AUTHOR]

The complex study of the river water and pore solutions from the bottom sediments in the lower reaches of the Razdol'naya River was conducted in February 2010. The major ion composition of the waters indicates the submarine origin of the near-bottom and pore waters in the lower reaches of the Razdol'naya River in the winter. The river estuary extends upstream for more than 20 km. It was established that the studied sediments are reduced oozes containing pyrite, hydrotroilite, and iron monosulfide, which is direct evidence for sulfate-reduction in the sediments. The diagenesis of organic matter is the main reason for the considerable decrease in the amount of sulfates and the increase in the alkalinity of the sediment pore water. The sedimentary pore water sampled from the deep river pits is characterized by excess alkalinity that cannot be explained by sulfate-reduction and methane genesis. It was suggested that the chemical weathering of silicate minerals and the bacterial mineralization of salts of organic acids could result in the excess alkalinity of the sediment pore water. [ABSTRACT FROM AUTHOR]

Seasonal variations in biogenic substances (nitrates, nitrites, ammonium, phosphates, and silicates), dissolved oxygen, dissolved organic matter, chlorophyll, humus, and suspended matter at seven stations on the Razdol'naya River are examined. Based on seasonal variations, the local sources of river water pollution by biogenic substances were identified. The annual and daily fluxes of biogenic substances through the Razdol'naya River into Amur Bay are calculated. A diffuse pollution source-agricultural fields in river valley-are shown to be the main source of biogenic substance fluxes. The vast hypoxia in the bottom water of Amur Bay, detected by the authors in 2007 and 2008, is supposed to be mostly caused by floods on the Razdol'naya R., which create favorable conditions of water blooming in Amur Bay in summer. The biomass of dead phytoplankton, experiencing microbiological decomposition and oxidation, causes hypoxia of bottom waters in the bay. [ABSTRACT FROM AUTHOR]