Measurements of pH, total alkalinity, and humic substance were carried out in June 2005 and 2006 in the waters of the Lower Amur between the cities of Komsomolsk-on-Amur and Nikolaevsk-on-Amur; 13 hydrochemical stations were examined at a distance of 489 km. In August 2016, hydrochemical observations were carried out at the mouth of the Amur River, which included measurements of pH, total alkalinity, humic substance, concentrations of the major ions in river water ( Na^ + , K+, Ca2+, Mg2+, Cl–, and SO_4^2 - ) and dissolved organic carbon. The average annual rate of chemical weathering in the Amur River basin was found to be 10.7 t/(km2 year). Weathering of rocks and photosynthesis of organic matter lead to the removal of CO2 from the atmosphere and form an annual export of atmospheric CO2 by the river into the marine environment, equal to 3.8 ×10^6 t C/ . -0emyear . It was established that the waters of the Amur River emit CO2 into the atmosphere at a rate of 4.5 ×10^6 t C/year. The balance of opposite processes (CO2 export and emission) showed that the Amur River ecosystem is a weak source of CO2 into the atmosphere. The annual flow of alkalinity from the Amur into the marine environment ( 1.65 ×10^11 mol/year) leads to an increase in the normalized alkalinity in the surface layer off the eastern shores of Sakhalin Island (Sea of Okhotsk) and in the northern part of the Sea of Japan.

In this study, the carbon dioxide (CO2) system on the continental shelf of the southwestern part of Peter the Great Bay (PGB), Sea of Japan was investigated during the autumn of 2015. During this season, the PGB represents an ocean-dominated shelf interaction system as the source of nutrients on the shelf is the subsurface part of the Sea of Japan. Weak seasonal upwelling occurred during the study period (October 20-23, 2015), forming a two-layer water structure on the shelf with a sharp pycnocline. The upper warm layer (12-15 degrees C) is characterized by nutrient depletion and supersaturation of dissolved oxygen concentrations (apparent oxygen utilization (AOU) < 0), and it simultaneously acts as a sink to atmospheric carbon dioxide (pCO(2)0) and an excess of carbon dioxide (pCO(2)>pCO(2atm)). Nitrate concentrations in the near-bottom layer of the waters suggest that these waters upwelled to the PGB shelf at depths of 200-300 m in the open Japan-East Sea. We observed a high intensity of photosynthesis corresponding to the pycnocline zone, with chlorophyll a concentration exceeding 10 mg/m(3), which was attributed to the phytoplankton bloom. The estimated primary production in the euphotic layer of the southwestern part of PGB is up to 4.98 gC m(-2) day(-1). Based on the dissolved inorganic carbon (DIC)/nutrient ratio in the subsurface waters of the northwestern Sea of Japan, the shelf becomes a sink for atmospheric carbon dioxide after upwelling. Owing to the heating of surface waters during summer, the PGB acts as a source of CO2 to the atmosphere.

The article presents the results of measurements of nutrients (including silicates, inorganic and organic forms of nitrogen, and phosphorus) in waters of the bays of the Shantar Archipelago (SA) in July 2016 and September 2022. It was found that photosynthesis predominantly removes inorganic forms of nitrogen and phosphorus from the surface waters of SA bays. River runoff leads to enrichment of SA waters in silicates and dissolved organic carbon. It was revealed that spawning salmon play an important role in enriching the apex of Akademii Bay with total phosphorus and nitrogen. Removal of nutrients from waters of SA bays by salmon fingerlings migrating to the open part of the Sea of Okhotsk in autumn has been shown. Application of the two-layer LOICZ model to SA waters showed that the main source of different forms of nitrogen and phosphorus are bottom waters of the open part of the Sea of Okhotsk (80–90

The data on parameters of biological productivity measured in the Academy Bay in September 2020, as chlorophyll a concentration in the euphotic layer, primary production, phytoplankton and zooplankton biomass, and results of echo sounding at 200 kHz are presented. The primary production estimated by Zvalinsky model varied from 300 to 6050 mgC per m2 per day. Diatoms with the biomass of 660–1220 mg/m3 dominated in phytoplankton, whereas Copepoda with the biomass ranged from 18 to 478 mg/m3 was the dominant zooplankton group. A discrepancy is noted between the measured net zooplankton biomass and thickness of the sound diffusion layer. The more productive area with the highest biomass of zooplankton was found in the northern Academy Bay enriched by nutrients transferred there from the Okhotsk Sea due to patterns of the estuarine circulation, but the thickest sound-diffusing layer was observed in the southern and central parts of the bay where it was presumably formed by shoals of juvenile fish rather than copepod aggregations. The feeding grounds of bowhead whales were located in the southern Academy Bay, too. This spatial misalignment of the feeding grounds with the highly productive area is explained by the hypothesis that juvenile fish may be important prey for whales, in addition to zooplankton.

Purpose. This study aims to analyze oxygen concentration data from the bottom waters of Amur Bay during the cold season and to identify the causes of its decrease in late February to March, when the bay remains ice-covered. Methods and Results. Variations in bottom water characteristics during the cold season were investigated in the area of summer hypoxia at a depth of 22 m (1 m above the seafloor) using the Water Quality Monitor autonomous bottom station (Wet Labs). Temperature, salinity (measured by conductivity), dissolved oxygen (DO), and chlorophyll a (measured by fluorescence) were recorded every 4 hours. Monitoring data from the cold period of 2013-2014 were compared with the data previously collected at the same station and location in summer 2011. The basic patterns of changes in oxygen content and the periods of dominance of production and organic matter mineralization in the bottom waters of Amur Bay during the cold season were identified. Conclusions. During the winter season, upwelling of the Japan Sea waters delivers nutrients to the bottom waters of Amur Bay. Enhanced vertical mixing, driven by low water column stability, supplies the euphotic layer with nutrients, enabling photosynthesis throughout the bay's water column. Over four months in winter, the Amur Bay waters become supersaturated with oxygen relative to atmospheric levels. The onset of the summer monsoon (late February to early March) initiates the formation of summer hypoxia in the bottom waters of Amur Bay.

Measurements of pH, total alkalinity, humic substances were carried out in June 2005, 2006 in the waters of the downstream Amur River along distance 489 km on the 13 hydrochemical stations between the cities of Komsomolsk-on-Amur and the Nikolaevsk-on-Amur. In August 2016, hydrochemical observations were carried out at the mouth Amur River, which included measurements of pH, total alkalinity, humic substances, concentrations of major ions of river water (Na+, K+K+, Ca2+, Mg2+, Cl–Cl–) and dissolved organic carbon. The average annual rate of chemical weathering in the Amur River basin has been established which equal to 10.7 t/(km2 year). Weathering of rocks and producing of organic matter by photosynthesis lead to the consumption of the atmospheric CO2 in the river basin. Amur River annually exports this atmospheric CO2 into the marine environment equaled to . It has been established that the Amur River waters annually emit of carbon dioxide to the atmosphere. The balance of opposite processes (CO2 export and CO2 emission) showed that the ecosystem of the Amur River is a weak source of carbon dioxide to the atmosphere. The annual export of total alkalinity by the Amur into the marine environment (mol/year) increases normalized total alkalinity in the surface layer off the eastern shores of the Sakhalin Island (Sea of Okhotsk) and in the northern part of the Sea of Japan.

Previously, studies of coastal eutrophication have usually focused on the nutrients input from adjacent land sectors, such as rivers, submarine-ground discharges, and atmospheric depositions. Here we report two examples of well-managed seasonal eutrophication phenomena in coastal marine environments, where nutrients come predominantly from offshore: one by humans and the other by nature (higher trophic animals). In the Sanggou Bay of North China, the total amount of incoming nutrients from the open Yellow Sea is taken up by seaweeds. Seaweed, in turn, supports bivalves culture activities and absorbs nutrients emitted by finfish. In the Academy Bay of Russian Far East, a relatively high plankton primary production sustains throughout the salmon-returning season when nutrients are released from the massive carcasses of dead fish after return from the ocean to their natal streams to spawn and die. This high plankton productivity, in turn, fuels higher trophic ecosystem constituents, including whale populations of global importance. In the future, dominance of nutrients from marine sources needs to be seriously considered in studies of coastal eutrophication.

Investigation of the interannual and short-term variability of the water parameters in the seas of Japan and Okhotsk and their ecological state were continued on cruises 77 of the R/V Professor Gagarinskiy and 97 of the R/V Akademik M.A. Lavrentyev in fall–winter 2021. CTD profiling and water sampling for chemical analyses, including methane and radioisotopes, were carried out. Autonomous bottom stations were moored for 2.5 months. Long-term trends of bottom water warming, eutrophication, and acidification of the Sea of Japan have been confirmed. The specific features of fall–winter restructuring of the field of currents in the northern Sea of Japan, multifrontality of the Sakhalin upwelling structure, and bimodality of the Primorye Current are shown.

The values of pH, total alkalinity, humic substance, chlorophyll a were measured in water in the Razdolnaya R. within 13 months in 2013–2014 at a station near Razdolnyi Settl. Estimates of the carbonate system of river waters showed that the major portion of the year, the river water was a source of CO 2 for the atmosphere with an annual emission flux of ~25 thousands tC/year. The chemical weathering of silicate rocks in the the Razdolnaya R. leads to withdrawal of atmospheric CO 2 . The mean annual export of the atmospheric CO 2 in the form of dissolved inorganic and organic carbon by the Razdolnaya R. into the Amur Bay (the Sea of Japan) was 47 thousands tC/year. Therefore, the the Razdolnaya R. ecosystem in the study period absorbed CO 2 (>20 thousands tC/year). The period of 2003–2017 showed a tendency toward an increase in the export of alkalinity, dissolved inorganic and organic carbon by the Razdolnaya R.. Estimates of the rate of chemical weathering of rocks, composing the basin, lie within 12–24 t/(km 2 year).

Our studies were carried out in July of 2016 in the Uda Bay and the Academy Bay (including the Ulban Bay and Nikolay Bay). The primary production (PP) of phytoplankton in the photic zone was calculated from the thickness of the euphotic zone, as well as by the concentration of chlorophyll a and the assimilation numbers of phytoplankton. We used a modified nonrectangular hyperbola model for photosynthetic light-response curves of phytoplankton for calculations. The formation of PP is a function of the supply of nutrients to the photic zone from the underlying waters by intense tidal currents under conditions of weak stratification. The high concentrations of humus substances in Uda Bay limited the growth of phytoplankton. The values of integrated PP varied between Uda Bay to Academy Bay from 250–1000 to 1069–4268 mgC m–2 day–1.

A noticeable feature of labile heavy metals is that they are highly prone to be to bioaccumulated and bioassimilated in natural environments. When in high concentrations, these metals are toxic to living organisms, as is particularly evident in the coastal shallow marine zones, which are most strongly affected by anthropogenic processes. This paper presents data on the contents of heavy metals, concentrations of organic carbon, and the granulometric composition of bottom-sediment cores in three shallow bights of the Peter the Great Bay, in two of which (Voevoda and Novgorodskaya bights), large bottom areas are overgrown with seagrass Zostera marina L. (sea zostera, ZM). Data on the vertical distribution of heavy metals and organic carbon in the cores showed that the highest concentrations of Zn and Cu (up to 204 and 91 mg/kg, respectively) occur in samples from Voevoda bight, and the highest concentrations of Mn and Pb (up to 344 and 45 mg/kg, respectively) were found in Novgorodskaya bight, where meadows of the seagrass grow. The highest Cr, Ni, and Co contents (up to 69, 31, and 13 mg/kg, respectively) were identified in Uglovoy bight, where sea grass is practically absent.

On cruise 80 of the R/V Professor Gagarinskiy from June 15 to July 18, 2022, integrated hydrographic and hydrochemical studies were carried out in Avachinskiy Bay of the Kamchatka Peninsula, on the northeastern shelf of Sakhalin Island, and in Peter the Great Bay to assess current environmental risks in the coastal zone of key areas of Russia’s Far Eastern seas and, in particular, to study possible abiotic factors that caused the mass mortality of marine organisms in Kamchatka in fall 2020. Comprehensive observations were performed, including CTD, hydrochemical water sampling, moorings, and plankton and bottom sediment sampling. An increased nutrient content was found, both in subsurface and intermediate Pacific waters, in comparison with 1990s–2000s data. Intensive snowmelt on adjacent mountain slopes during the survey period showed the significant impact of continental runoff on the hydrochemical characteristics of Avachinskiy Bay waters, causing decreased salinity and significantly increased concentrations of nutrients and chlorophyll a in the coastal zone. The dynamics of mesoscale eddies ensures transport of coastal waters to the ocean over a distance of more than 100 nautical miles. The results suggest that the catastrophic phenomenon off Kamchatka, associated with anomalous harmful algae blooms, is due to conjugate biogeochemical and hydrographic factors: river runoff and intrusion of deep waters on the shelf caused by coastal wind and dynamic upwelling during the period of maximum warming and eutrophication of subarctic Pacific waters, as well as the orographic and topographic features of Avachinskiy Bay.

The hydrological and hydrochemical data of surface and bottom waters of Academy Bay were obtained on two POI FEB RAS cruises carried out from July 11 to 14, 2016 and from September 15 to 19, 2020. Observations in 2016 were carried out during the summer flood and after thawing sea ice in the bay which were confirmed by the hydrological characteristics of the waters. Supersaturation of bottom and surface waters with atmospheric oxygen and undersaturation with atmospheric carbon dioxide indicate that production processes dominate in the bay. However, low contents of nutrients and chlorophyll a in the bay and in the estuaries of the Syran and Ulban rivers characterize the bay as rather an oligotrophic basin. This is supported by the common procedure of eutrophication assessment. In September 2020, the majority of bottom waters were undersaturated with oxygen and supersaturated with carbon dioxide, meaning organic matter degradation processes dominated. In the fall 2020, the apex of Ulban Bay was characterized by very high concentrations of dissolved inorganic phosphorus, reaching 10–14 μmol/L, and by chlorophyl a concentrations of surface waters higher than 10 mg/m 3 . Values of obtained parameters suggest that waters of Academy Bay have high eutrophic status. The difference between observations implemented in 2016 and 2020 cannot be explained by the interannual variability of the hydrochemical parameters of the waters of Academy Bay, rather it can be explained by an additional episodic source of nutrients that occurs in the late summer–autumn season. Salmon that died after spawning can serve as such an source. These dead salmon provide eutrophication of Academy Bay waters. High eutrophic waters probably provide the feeding base for polar whales.

The activity of dissolved radium isotopes 223Ra, 224Ra, 228Ra, the concentrations of nutrients: ammonium, nitrates, nitrites, phosphates, silicates, total nitrogen, and total phosphorus are studied in the Razdolnaya River estuary at suspension concentration in river water >1000 mg/L. During flood, classical two-layer estuarine circulation was observed over the nearshore; this circulation was formed by a discharge current and compensation flow from the depth of 20 m to the depth of 8 m. The main source of 228Ra inflow into the estuary is desorption from river suspension in the beginning of the mixing zone near the mouth bar, where its activity reached 163 ± 0.03 dpm 100 L–1, which is 139 times that in the river water. The zone near the river mouth bar shows higher activity of 224Ra and 223Ra (4 and 17 times greater than that in river water) and an increase in the concentrations of total phosphorus, $${\text{NH}}_{{\text{4}}}^{ + }$$ , DSi, $${\text{NO}}_{{\text{3}}}^{ - }$$ , and total nitrogen. An extremum in the activity of 224Ra (65.41 ± 0.68 dpm 100 L–1) and an increase in 223Ra (1.97 ± 0.11 dpm 100 L–1) were recorded in the bottom water of the nearshore; therefore, the main source of these isotopes is bottom sediments. Direct correlation was found to exist in the pairs $${\text{PO}}_{4}^{{3 - }}$$ – 224Ra and $${\text{NH}}_{{\text{4}}}^{ + }$$ – 224Ra, and simultaneous extremum was recorded in 224Ra, $${\text{PO}}_{4}^{{3 - }}$$ , and $${\text{NH}}_{{\text{4}}}^{ + }$$ in bottom nearshore waters; this extremum is attained in the area with highest density of colonies of polychaetes polychaetes―active bioirrigtors of pore waters.

Fluxes of nutrients (ammonium, total nitrogen, dissolved inorganic phosphorus, total phosphorus, silica, and dissolved organic carbon) across the interface between bottom water and sediments were studied in three shallow bights (Voevoda, Novgorodskaya, and Uglovoj) of the Peter the Great Bay in the course of survey in September–October, 2019. At two stations in each of the bights, nutrient concentrations were measured in seawater sampled at 10 cm above the seafloor and in the pore waters of the sediment cores; and organic carbon, fulvic acids, humic acids, and chlorophyll a were analyzed in the solid phase of the sediments. Bioturbation coefficients were estimated from variations in chlorophyll a concentration with depth in the sediment cores. The fluxes of nutrients (ammonium, total nitrogen, phosphorus, total phosphorus, and silicon) and dissolved organic carbon (DOC) were evaluated by model calculations. The estimated nutrients fluxes were, with regard to the bioturbation, about one order of magnitude higher than those estimated by the Fick law. The highest concentrations of organic carbon, 6.5 and 5.5% per dry weight of sediments, were found in the top layer of sediments retrieved at sites covered by Zostera marina L. in the Voevoda and Novgorodskaya bights, respectively. However, the highest fluxes across the water–sediment interface were obtained for a site devoid of seagrass in the Novgorodskaya bight, where the top sediment layer contained 2.8% organic carbon. The annual specific fluxes of nutrients estimated for the water–sediment interface were comparable to or even higher than the annual specific fluxes of nutrients brought per surface area unit of the Amur bay by the Razdolnaya River and domestic waste waters from the city of Vladivostok.

Восточный шельф о. Сахалин относится к акваториям с высокой биологической продукцией. Важная его особенность заключается в наличии районов нагула для охотско-корейской популяции серых китов. Цель данной работы - определить особенности формирования первичной продукции в данном регионе. Для этого в период с 7 по 9 июля 2016 г. были проведены гидрохимические исследования северо-восточного шельфа о. Сахалин. На каждой станции с поверхностного и придонного горизонтов проводили отбор проб воды с последующими измерениями концентраций хлорофилла а, нитратов и фосфатов. Также на каждой станции проводили вертикальное зондирование водной толщи с помощью зондов Sea-Bird SBE19plus V и Rinko Profiler, оснащенных датчиками давления, температуры, электропроводности, флуоресценции хлорофилла, растворенного кислорода, мутности и фотосинтетически активной радиации. Датчиками кислорода кислорода ARO1-USB RINKO фирмы JFE Advantech Co., Ltd. в условиях in situ провели измерение ассимиляционного числа фитопланктона. По результатам исследований рассчитывали первичную продукцию фитопланктона в фотическом слое. Для расчета использовали представление световой кривой в модифицированной модели непрямоугольной гиперболы. Формирование первичной продукции происходило наиболее интенсивно в зоне влияния р. Амур, а значения интегральной первичной продукции в фотическом слое вод изменялись от 1,57 до 11,17 гС м-2·сут-1. Область распространения модифицированных высокопродуктивных вод р. Амур достигала траверза южной границы залива Пильтун, где была ограничена холодными солеными глубоководными водами, привнесенными вихревой структурой. Доля продукции, затрачиваемой на формирование кормовой базы охотско-корейской популяции серых китов составила 1,9 % от общей продукции рассматривеемой акватории.

The eastern Sakhalin Island shelf is the area of high biological production. Its key peculiarity is the presence of a feeding area for the Okhotsk–Korean population of gray whales. We aimed at determining the features of the formation of primary production in this area; thereby, on 7–9 July, 2016, hydrochemical studies on the northeastern Sakhalin Island shelf were carried out. At each station, water was sampled from surface and near-bottom layers; then, concentrations of chlorophyll a, nitrates, and phosphates were measured. Moreover, at each station, depth profiling was conducted by a Sea-Bird SBE 19plus and a Rinko-Profiler. Those profilers were equipped with sensors for pressure, temperature, electrical conductivity, chlorophyll fluorescence, dissolved oxygen, turbidity, and photosynthetically active radiation. Assimilation number for phytoplankton was measured in situ by ARO1-USB Rinko dissolved oxygen sensors (JFE Advantech Co., Ltd.). Phytoplankton primary production in the photic layer was determined by the light model based on the representation of the photosynthetic light-response curve in the modified model of the non-rectangular hyperbola. Most intensively, the primary production occurred in the area affected by the Amur River. In the photic layer, the values of integral primary production varied within 1.57–11.17 g C·m−2·day−1. The distribution area of the modified highly productive water of the Amur River reached the traverse of the southern boundary of the Piltun Bay; there, it was limited by cold salty water which had risen due to the eddy structure from deeper horizons. The ratio of the production spent on the food supply formation for the Okhotsk–Korean population of gray whales was 1.9 % of the total production of the studied water area.

In the period of summer flood 2016, a number of chemical characteristics associated with carbon cycle were studied in the estuaries of the Syran and Ul’ban rivers in the area of the Shantarskii Archipelago with the total water discharge of 194.7 m3/s. The zone of mixing at the salinity of <20‰ is the source of CO2 for the atmosphere with the estimated CO2 flux up to 112.7 mmol m−2 day−1. At the salinity >20‰, the thickness of the photic layer increases abruptly and photosynthesis starts to dominate, resulting in the formation of CO2 flow from the atmosphere into water with a rate of up to 30 mmol m−2 day−1. A model CO2 flow at the water/atmosphere interface is presented at a wind speed from 2 to 15 m/s for the entire mixing zone, the water in which generally absorb atmospheric CO2. A specific feature of the basin compared with the estuaries of the Uda and Usalgin rivers in the zone of the Shantarskii Archipelago is the combination of the relatively low volume of water and solid runoff with a relatively high phosphorus flux in mineral and organic forms.

The article presents the data of an comprehensive expedition of the Pacific Oceanological Institute, Far East Branch, Russian Academy of Sciences, performed in the mixing zones of the Uda and Usalgin rivers in July 2016. During the flood period, they occupy most of the catchment basins: Udskaya Bay and Nikolaya Bay. The estimated discharge of the Uda and Usalgin rivers was 4390 and 173 m3/s, respectively, and estuarine waters with salinity to 8‰ spread from their mouths to a distance of 25 km in Udskaya Bay and 2.5 km in Nikolaya Bay. The boundary of the estuarine seashore distinguished by the isohaline 30‰ was at a distance of 85 km from the river mouths in the both mixing zones. River runoff—the main supplier of suspended particulate matter and silicates—limited the thickness of the photic layer and photosynthesis at the early stage of mixing zones to the salinity of ~24‰, where water was a source of CO2 for the atmosphere. At the later stage of the mixing zones, under the conditions of a greater thickness of the photic layer, production dominated, and the water area was a sink for atmospheric CO2. Mineralization of autochthonous organic matter on the bottom of the receiving basins was the main source of inorganic forms of nutrients. The lack of silicates (DISi/DIN < 1 and the relatively low DIN/DIP ratio in the range of 1.8–8) was a limiting factor of photosynthesis at the late stage of the mixing zone.