The production characteristics of phyto- and bacterioplankton were obtained on the Transatlantic transect along the route of cruise 79 of the R/V Akademik Mstislav Keldysh in the Atlantic Ocean in December 2019–January 2020. These data were analyzed taking into account the biogeographic zoning of the study region, determined by various hydrometeorological conditions. Primary production (PP) was 0.8–34.2 mgC m–2 day–1 with an average value of 8.9 mgC m–2 day–1 in the euphotic zone. The daily assimilation number on the transect varied in surface samples from 7.2 to 260.1 mgC mgChl–1 day–1. Chlorophyll a concentrations ranged from 0.01 mg/m3 in the SASTG region to 0.59 mg/m3 in the NASTG province. Integrated primary production varied from 258 to 765 mgC/m2. The bacterial production (BP) in the surface horizons varied from 0.04 to 16.1 mgC m–3 day–1 with an average value of 3.7 mgC m–3 day–1; the maximum values were observed in the Lomonosov Current with a maximum at a depth of 160 m. Bacterial production in the water column varied from 23.2 mgC/m2 to 6182.7 mgC/m2. We suggest that the highest bacterial production observed in deep-sea horizons is associated with high concentrations of DOM.

The features of the empirical bio-optical algorithm operation in the waters around the Antarctic Peninsula are analyzed based on a comparison of calibrated data from the shipborne flow fluorimeter and satellite data from the OLCI radiometer on Senti nel-3A and Sentinel-3B satellites during the Antarctic summers of January-February 2020 and 2022. It is shown that the standard OC4 bio-optical algorithm significantly underestimates satellite estimates of Chl-a concentration from ~1.5 to ~9 times (on aver age by a factor of ~3.1). The known regional OC4-SO algorithm provides acceptable errors of Chl-a concentration estimates and can be used for studies related to the analysis of Chl-a concentration in the waters around the Antarctic Peninsula. The developed in this work new regional algorithm OC4-AP has significantly lower error in comparison with the known standard and regional algorithms. It can be used if it is necessary to obtain a remote estimate of the concentration of Chl-a, as close as possible to the accumulated world experience in determining this value by standard extract spectrophotometric and fluorimetric methods. The observed underestimation of satellite estimates of Chl-a concentration using the standard empirical bio-optical OC4 algorithm can be attributed to at least three reasons typical for the studied water area: low relative CDOM content, high phycoerythrin content, and stronger effect of pigment packing in phytoplankton cells compared to the average values in the World Ocean.

The horizontal and vertical chlorophyll- a concentrations ( Chl ) distributions along the ship route of 79 th cruise of R/V “Akademik Mstislav Keldysh” in the Atlantic Ocean in December 2019—January 2020 were obtained. Analysis of the observations was conducted for the biogeochemical provinces which were determined by means of the different hydrometeorological conditions for the phytoplankton community functioning. Three methods of Chl measurements were applied: standard extraction method of the seawater samples, the fluorometer underway measurements in the flow-through water system at the depth of 5 m and in-situ profiling fluorometer measurements at stations. Also, measurements of the seawater temperature and salinity in the flow-through water system, the CTD and optical profiling, and ARGO floats were used. The maximum Chl values in the near-surface ocean layer are observed at zones of divergence in the Canary upwelling systems (CNRY) (1.3 mg/m 3 ) and in the Falkland (Malvinas) Current system (4.8 mg/m 3 ) , and also in the Drake Strait (1.2 mg/m 3 ) . The least Chl values (0.01–0.12 mg/m 3 ) are observed in the tropical, equatorial areas and in the South Atlantic Subtropical Anticyclonic Gyre (SASTG) at the ship route. Vertical Chl profiles with absence of the significant Chl maximum were found. In the CNRY region the Chl values were not changed much within the euphotic zone. While in the region of the Antarctic Circumpolar Current in the Drake Strait and in the offshore stream of the Falkland Current the quasi-homogeneous Chl profiles were observed in the upper layer which is almost 2 times deeper than the euphotic zone. In the profiles with the significant local Chl maximum the most Chl value of 3.5 mg/m 3 i s observed at the depth about 12 m in the upwelling region on the Patagonian Shelf. In other regions the depth of Chl maximum localization (0.2–0.9 mg/m 3 ) varies widely from 25 to 120 m. In the western part of the SASTG region the absolute Chl maxima were found at the depth of 120 m, that is deeper, then the euphotic zone which is equal to 100 m.

Areas with different values of the bio-optical characteristics of the surface water layer and different temperature and salinity distributions obtained during a Transatlantic transect in winter 2019/2020 are studied. In the region of Canary Upwelling and the equator, the temperature decrease zones correspond to peaks of fluorescence intensity of chlorophyll and colored dissolved organic matter (CDOM). The fluorescence intensities concurrently varied in the both channels. In the surface water of the tropical and subtropical Atlantic, low values of the chlorophyll and CDOM fluorescence intensities and the attenuation and absorption coefficients, which are characteristic of oligotrophic waters, were recorded. These distributions mostly agree well with the NOAA web service, created in late 2019 and providing interpolated satellite maps of chlorophyll a concentration. En route to La Plata Bay, a series of fronts were recorded, as well as a strong negative correlation between the CDOM fluorescence intensity and salinity (ρ = –0.97), caused by river runoff. In contrast to a similar negative correlation studied earlier in the Kara Sea, CDOM photodegradation under the action of high-intensity sunlight was observed.

Seawater properties in two intense rings in the South Atlantic are considered. One ring separated from the Brazil Current and the other from the Malvinas Current. The analysis is based on the CTD casts and SADCP measurements from the onboard velocity profiler. The optical properties, chemical parameters, methane concentration, and biological properties such as primary production, plankton, and fish were also analyzed. Analysis of strong differences between the eddies is supplemented by observations of whales and birds in the region.

Satellite data on sea surface temperature and temperature and salinity profiles in the northeastern shelf of Sakhalin showed that during the periods of advection of warm and low-salinity water to the eastern shelf of Sakhalin, intensive coastal upwelling did not develop, even under favorable wind conditions. Regular deepening of the thermocline/halocline has prevented the rise of cold and salt water to the sea surface. Numerical experiments with the INMOM-JRA55-do model showed a significant deepening of the thermocline/halocline accompanied by the increasing density stratification, which prevented the elevating of the Sea of Okhotsk water to the sea surface. It is assumed that the joint monitoring of wind conditions and hydrology on the eastern shelf of Sakhalin in the second half of the year will significantly clarify the features of its development and more accurately assess the biological productivity of water in this area of the Sea of Okhotsk.

The effect caused by the typhoon Goni in the coastal water of Posyet Bay, the Sea of Japan, is considered. In nearshore expeditions, profilograph SBE-19plus was used to measure the hydrological characteristics: water temperature and salinity, as well as the hydrobiological characteristics of the fluorescence of chlorophyll a and dyed dissolved organic matter a week after the passage of the typhoon. To reveal the effect of the typhoon on the ecosystem, the data measured after typhoon passage were compared with the appropriate characteristics obtained in the same season in about the same place a year before, when there was no typhoon. A high correlation was found to exist between chlorophyll a concentration and the input of fresh water from the continent. It was shown that the dyed dissolved organic matter is determined, in addition to the continental export, by autochthonous processes. The problem formulated in the study was solved with the involvement of satellite data, which reflected changes in the ecosystem in large water areas and suggested the conclusion that the changes caused by the typhoon shift the state of the coastal zone toward that of river estuaries.

In this paper we explore the possibilities of applying satellite ocean colour (OC) observations and SST to study the changes in the conditions of hypoxia in the near-bottom water in the western part of Peter the Great Bay. Near-bottom water hypoxia occurs in water bodies with increased organic matter influx when the dissolved oxygen (DO) consumed at its oxidation is not restored. Consumption of most DO is usually attributed to the oxidation of organic matter formed as a result of increased algae growth during water eutrophication. Satellite data on indicators of phytoplankton (chlorophyll-a concentration (Chl) and fluorescence (FLH)) allow to analyze the spatial-temporal changes of this substation. Coloured dissolved organic matter (CDOM), non-algal particles (NAP) influence on satellite Chl estimates and also on near-bottom water hypoxia formation. This study analyzes daily, seasonal, and inter-annual changes in the distributions of indicators (Chl, FLH, the coefficients of light absorption by coloured detrital matter (a(CDM)) and light backscattering by suspended particles (b(bp))), based on the instant satellite OC data from MODIS-Aqua. Data on the Chl, the sea surface temperature (SST) from the MODIS-Aqua, the precipitation from the TRMM satellite and the hydrometeorological stations (HMSs), the wind speed and direction from HMS "Vladivostok" are used to study the influence of hydrometeorological conditions on the Chl values. These distributions were compared with the literary information based on field observations of the hypoxia cases in the same area and with the changes in the vertical DO, Chl, temperature, salinity distribution obtained by coastal expeditions in October-November 2010 and February-March 2011. Significant interrelations within 95% confidence level between the satellite Chl, FLH values calculated at the MUMM atmospheric correction and in situ Chl values obtained in the autumn of 2010 were reached separately for the cases with winds of northern and southern directions with the correlation coefficients of 0.71, 0.48 and 0.49, 0.71, respectively. Significant dependences of Chl on SST and Chl on wind speed explained by the influence of continental runoff and water ventilation were obtained. Therefore, the changes of Chl reflect the changes of hypoxic conditions in the near-bottom water. In Amursky Bay the onset of hypoxia was at the Chl and SST values equal to 4 mg m(-3) and 13 degrees C (up arrow) - at increasing SST); near Furugelm Island it was at 1.6 mg m(-3) and 25 degrees C (up arrow), 1 mg m(-3) and 21 degrees C (down arrow). The difference in the Chl values was reflected in the hypoxia onset timings that were the beginning of June (2011), August (2013), and September (2014), respectively. The water flow from the eastern coast of Amursky Bay in early August of 2013 recorded from the OC and SST satellite imagers appeared in an additional hypoxic zone. Decreased OC characteristics in the runoff of the Razdolnaya River in August-September of 2014 were a sign of hypoxia at its mouth. Near Furugelm Island the hypoxia destruction (increase in the DO level from 1 to 4.5 ml L-1 was observed at the Chl of 0.9 mg m(-3) and SST = 18 degrees C (down arrow). At the autumn maximum of Chl equal to 1.7 mg m(-3) and SST = 4 degrees C (down arrow) in mid-November the DO level here increased to 8 ml L-1. In Amursky Bay, short-term destructions/weakening of hypoxia manifested themselves in sharp increases of Chl. At that, the ratio between the Chl value and the approximation level was equal to 2 and higher for SST equal to 22-25 degrees C (up arrow), to 0.9 and higher for SST equal to 5-13 degrees C (down arrow). With the water stratification destruction in temperature and the noticeable weakening of the stratification in salinity (mid-November), the hypoxia destructed (the DO level increased from 2 to 6 ml L-1). In this case, Chl and SST were about 3 mg m(-3) and 5 degrees C (down arrow). (C) 2020 COSPAR. Published by Elsevier Ltd. All rights reserved.

A study and comparative analysis of production characteristics of bacterio- and phytoplankton in Avacha Bay and in the southern region of the Far Eastern State Marine Biosphere Reserve (FEMBR) in Posyet Bay was carried out in summer, 2017. Bacterial production in the surface samples from these basins was similar, varying from 0.28 to 2.3 mg C/(day m3) for Avacha Bay and from 0.22 to 2.0 mg C/(day m3) for FEMBR, while the number of bacterioplankton cells was significantly higher at the FEMBR site, reaching 2.1 ×106 cells/mL. Evidence of hypoxia in the relief depressions of both water areas was noted. Bacterial oxygen consumption was found to be one of the main factors in development of hypoxia in Avacha Bay. Primary production in the surface samples and in the water column in both basins was comparable, but the concentration of chlorophyll a in the FEMBR southern region was more than an order of magnitude lower. This ratio resulted from absorption by other organisms of most of the produced microalgae biomass in the water column and a higher assimilation number, which increases from high to low latitudes. On the contrary, in Avacha Bay both high levels of primary production and a high concentration of chlorophyll a were noted, which indicated an intensive terrigenous influx of biogenic elements of a natural and anthropogenic nature.

Primary production of the Avacha Bay in summer 2017. S.P. ZAKHARKOV1, E.V. LEPSKAYA2, O.B. TEPNIN2,E.A. SHTRAIKHERT1, T.N. GORDEICHUK1 (1V.I. Il’ichev Pacific Oceanological Institute, FEB RAS, Vladivostok,2KamchatNIRO, Petropavlovsk-Kamchatsky). The paper presents the results of a study of the spatial and temporal variability of the primary production of phytoplankton (PP) in the Avacha Bay of the Pacific Ocean in summer 2017. For the first time, measurements of PP by the radiocarbon method, mainly in the near-surface layer of water, conducted once a month, are published. Primary production in the water column was calculated by the formulas proposed by M. Behrenfeld and P. Falkovski. It is assumed that the level of PP in this season is determined by the following factors: the input of biogenic elements with a river runoff, turbidity and water temperature in the photic layer. The values of PP and the average concentrations of chlorophyll-a (Chl-a) allow us to attribute the bay to eutrophic water bodies.At the same time, the Chl-a concentration values obtained by instrumental and remote sensing were compared. Theneed for remote data correction was identified.

The vertical distribution of the concentration of chlorophyll a (Chl) and colored dissolved organic matter (CDOM), temperature (T), and salinity (S) were studied at two diel stations located at close coordinates and performed at a weekly interval and seven stations spaced 1 mi apart on hydrological section in the shelf zone of Possjet Bay (Sea of Japan) in the autumn of 2014. The Chl concentration was estimated from fluorescence intensity (FChl). In the surface layer of the diel stations, the Chl concentration varied within ± 10% of the mean value. In the water column, a negative correlation of FChl with T and a positive relationship of S with CDOM were established at both stations. At all stations, the maximum Chl concentration occurred under the seasonal pycnocline layer.

Production parameters for bacterioplankton were assessed during the spring–summer period in the western parts of the Sea of Okhotsk and the Bering Sea, as well as in northwestern Pacific Ocean. The lowest values of bacterial production were observed in early June during the spring phytoplankton bloom (0.08 mg C day–1 m–3), while the maximum values (up to 55 mg C day–1 m–3) occurred in late July‒early August, 1.5 to 2 months after the bloom. The concentration of dissolved organic matter, the substrate for bacterioplankton, was assessed using satellite data. The ratio between bacterial and primary production in the surface samples varied from 0.5% at the peak of phytoplankton bloom to 180% at the peak of bacterioplankton development.

Variability of the bio-optical characteristics may be as indicator of changes in the functioning of ecosystems, for example the eutrophication, the organic matter pollution and the hypoxia of water body. In this work we study according to data, obtained by means of the satellite MODIS-Aqua spectroradiometer, the variability of bio-optical characteristics (concentration and fluorescence of chlorophyll-a (Cchl and Fchl), coefficients of light absorption by detritus and yellow substance (adg) and light backscattering by suspended particles of mineral and biological origin (bbp)) along sections extending from the shelf (Amur and Ussuri Bays) toward the seaward area of Peter the Great Bay from January to December of 2007, 2008, 2013, 2014. Features of the seasonal Cchl satellite variability along the selected sections were shown. It is noticed that the highest Cchl satellite values are characteristic for the Amur Bay, usually from place of confluence of the Razdolnaya River from late May - June to August – September. Separate cases of increased values of bbp in area, which stretches from the Vladivostok coast, were revealed. In the first case, the area of the increased values of bbp corresponded to area, having the Fchl values close to zero, and in second case – to area with the increased Fchl. Possible, the first case can be caused by the increase in content of the mineral origin suspension because of some building works, and the second case is due to the discharge of water by reservoirs. It is noticed that the increased values of bio-optical characteristics except Fchl are characteristic for the scenarios with the increased wind speed and after the atmospheric precipitation. Increased Fchl values are characteristic at the sufficient rainfall, contributing to rising of the rivers level, or the increase of wind speed to about 8 m/s and above.

The spatial variability of chlorophyll a concentrations was studied from the data of two near-shore expeditions and the cruise of the R/V Akademik M.A. Lavrent’ev in October–November 2010 over the northwestern part of the Sea of Japan. The sections across eddies showed a maximum of chlorophyll a at a depth of 40 m. According to the data from the cruise, the chlorophyll a concentration was maximum in the north of the sea and decreased to the south. In parallel, the procedures for chlorophyll a determination were compared for spectrophotometry with a fluorescence probe and a fluorescence flow system. The probe data of chlorophyll a fluorescence showed a high correlation with the chlorophyll a concentrations by spectrophotometry. On the contrary, data on chlorophyll a concentrations from spectrophotometry did not agree with those from the flow system. It was shown that a fluorimeter in the flow system recorded dissolved organic matter along with the chlorophyll a fluorescence.