The role of zooplankton in the transformation of the organic matter in the Ob estuary,on the shelf,and in the deep regions of the Kara Sea

The data for the present study were collected at 20 sampling stations in the Kara Sea along the transect from the Ob estuary to the deep sea St. Anna Trough in September 2007. Based on the hydrophysical features, the distribution of the Chl a, and the primary production, we distinguished six habitats: the river, estuary, inner and outer shelf, continental slope, and trough. The impact of the small-size (<0.5 mm) and large-size (>0.5 mm) fractions of the zooplankton on the phytoplankton’s organic carbon in the different regions of the Kara Sea was estimated. The ingestion rate was assessed using the analysis of the gut fluorescence content and the gut evacuation rate. The zooplankton grazed 1–2% of the phytoplankton biomass in the river and estuary; 3.5% over the shelf; and 6 and 10% in the regions of the trough and slope, respectively. The grazing impact of the small-sized zooplankton increased from the river zone to the deep regions (from 1 to 90%) along with their share in the total zooplankton abundance (from 18 to 95%). From 72 to 86% of the primary production was grazed over the shelf and slope. The primary production did not cover the feeding requirements of the zooplankton in the estuarine regions and St. Anna Trough in the autumn. In the estuarine regions, the major portion of the organic matter settles on the bottom due to the strong inflow of the allochthonous matter and the relatively low zooplankton grazing.     

Bacterial and primary production in the pelagic zone of the Kara Sea

Data on the bacterial and primary production, which were obtained simultaneously for the same water samples, are presented for three regions of the Kara Sea. The samples were collected for the transect westwards of the Yamal Peninsula, along the St. Anna Trough, and the transect in Ob Bay. Direct counts of the DAPI-stained bacterial cells were performed. The bacterial production and grazing rates were determined using a direct method when metabolic inhibitors vancomycin and penicillin were added. The primary production rates were estimated using the ¹⁴C method.     

Laboratory and marine study of photoluminescent sensors of oxygen dissolved in seawater

The laboratory and marine study of photoluminescent sensors developed at the TsAGI has been conducted to create a highly sensitivity gauge of the oxygen dissolved in seawater. The advantages of the photoluminescent gauge over the electrochemical ones are the following: zero sensitivity to electromagnetic fields, the pH of the water, and the hydrogen sulphide and ions of heavy metals in the water; zero oxygen consumption; and no need for the water to be pumped through the device.     

Spatial variability of the primary production and chlorophyll <Emphasis Type="Italic">a</Emphasis> concentration in the drake passage in the austral spring

The spatial distribution of the primary production (PP) and the chlorophyll a concentration (Chl) were investigated during two research cruises in the Drake Passage area in October–November of 2007 and 2008. The algorithm evaluating the integral PP (PP_int) for the water column in this area was developed based on the data on the surface chlorophyll (Chl_s) and the incident solar irradiance obtained in 2004–2008 in the Atlantic Sector of the Southern Ocean. The results obtained both by the experimental and model approaches suggested that the Polar Front (PF) region of the Drake Passage was characterized by low values of both the PP_int (<100 mg C/m² per day) and Chl_s (0.08–0.20 mg/m³) in October–November. Low values of the Chl_s and relatively high phaeophytine a concentrations indicated the winter succession state of the phytoplankton community in the Antarctic Ocean and the southern Polar Frontal Zone (PFZ). The seasonal warming of the surface water layers and the developing pycnocline resulted in a phytoplankton bloom and a Chl_s concentration of more than 1 mg/m³ in mid-November in this area and the Subantarctic waters.     

Structure and Productivity of the Phytocenosis in the Southwestern Kara Sea in Early Spring

Results of plankton biota studies in the southwestern Kara are presented. The spatial distribution of hydrochemical and hydrophysical parameters related to structural and functional characteristics of phytoplankton in the surface water is considered. The chlorophyll a concentration varied in the surface layer of the Kara Sea from 0.08 to 3.22 mg m^–3 (mean value 0.62 mg m^–3). Primary production varied from 0 to 1.92 mg C m^–3 day^–1 (the mean value of 0.42 mg C m^–3 day^–1) in the ice-covered water areas and was greater by a factor of four, ranging from 1.01 to 3.46 mg C m^–3 day^–1 (the mean value of 1.79 mg C m^–3 day^–1) in ice-free areas. In this case, the total algal biomass varied from 0.8 to 110.7 mg C m^–3 (mean value 10.6 mg C m^–3). It is shown that in the study period, waters from the western Kara Sea were more productive than the estuarine water areas of the Ob and Yenisei rivers. The activity of phototrophic phytoplankton in river waters was almost completely absent. It is established that the contents of nutrients and iron were higher than the threshold for limitation of phytoplankton development. The experiments showed that the production activity of phototrophic algae is restrained by light deficit beneath the ice.     

Effect of Mercury Chloride on the Chlorophyl <Emphasis Type="Italic">a</Emphasis> and Pheophytin Content in Marine Microalgae: Measuring the Flow of Autotrophic Phytoplankton Using Sediment Traps Data

The present work aimed to study the influence of mercuric chloride (HgCl₂) on pigment content (chlorophyll a and pheophytin) in sediment traps on the basis of experimental data. The marine microalgal cultures of Conticribra weissflogii (Mediophyceae), Tetraselmis viridis (Chlorodendrophyceae), Amphidinium carterae (Dinophyceae), Nannochloropsis sp. (Eustigmatophyceae) were used. The obtained results revealed that the influence of mercury on pigment content as well as on photosynthetic activity was different in different species. The considerable decrease in phytopigments content was observed in Amphidinium carterae and Conticribra weissflogii, while the proportion of pheophytin increased. The pigment content of Tetraselmis viridis was not different from the control line, while for Nannochloropsis sp. the increase in pigment concentration was noticed. The complete immediate inhibition of photosynthetic activity was observed in Conticribra weissflogii, Tetraselmis viridis, Amphidinium carterae, while Nannochloropsis sp. responded only after 24 h of exposition. The pigment degradation rate was almost the same for diatoms and dinoflagellates. The equation for estimating the phytopigments content in sediment traps, that takes into consideration the exposition time, is proposed.     

Distribution of the primary production and chlorophyll <Emphasis Type="Italic">a</Emphasis> in the Kara Sea in September of 2007

The studies were performed from September 10 to 29 of 2007 in the Kara Sea in transects westward of the Yamal Peninsula, near the St. Anna Trough, in the Ob River’s estuary, and on the adjacent shelf. The concentration of chlorophyll a in the euphotic layer changed from 0.02 to 4.37 mg/m³, amounting on the average to 0.76 mg/m³. The primary production in the water column varied from 10.9 to 148.0 mg C/m² per day (the mean was 56.9 mg C/m² per day). It was shown that frontal zones divided the Kara Sea into distinct areas with different productivities. The maximum levels of the primary production were measured in the deep part of the Yamal transect (132.4 mg C/m² per day) and the shallow Kara Sea shelf near the Ob River’s estuary (74.9 mg C/m² per day). The characteristics of these regions were the low salinity of the surface water layer (19–25 psu) and the elevated silicon content (12.8–28.1 μg-atom Si/l), which is explainable by the river water inflow. The frontal zones of the Yamal Current in the Yamal and Ob transects displayed high values of the assimilation numbers, amounting to 2.32 and 1.49 mg C/mg of chlorophyll per h, respectively (the maximal for the studied regions).     

Meridional asymmetric distribution of the primary production in the Atlantic Sector of the Southern Ocean in the austral spring and summer

The spatial distribution of the phytoplankton productivity was investigated in the Atlantic Sector of the Southern Ocean in the austral summer of 2009?C2010 and the spring of 2010 on the basis of field measurements. In October?CNovember, the average integrated primary production and the concentration of surface and integrated (photosynthetic layer) chlorophyll ??a?? in the Subantarctic waters of the Drake Passage exceeded the similar values along the Greenwich meridian by 3, 2, and 1.5 times, respectively. Similar primary production was observed in December?CJanuary for the water column in the eastern and western sectors of the studied area. The chlorophyll ??a?? concentration in the surface water layer was higher by 1.7 times for the Greenwich meridian area compared to the deep layers, but the concentrations of this pigment in the deeper layers did not differ. During the spring, the average primary production in the water column (the chlorophyll ??a?? concentration in the surface and in the photosynthetic layer) differed in the Drake Passage and along the Greenwich meridian by 2.3, 1.6, and 1.7 times, respectively. The opposite pattern was observed during the summer period, when the parameters listed above were higher for the Greenwich meridian area by 1.9, 2.5, and 1.7 times, respectively. Therefore, the western Antarctic areas in the spring are characterized by higher production than the eastern ones, and an opposite pattern is observed in the summer. The possible reasons for the meridional zonation of the chlorophyll ??a?? and the primary production are discussed in regard to different seasons.     

The structure and distribution of the phytoplankton community in the deep region of the Northern Kara Sea

The phytoplankton community and its distribution were investigated in the eastern branch of the St. Anna Trough and over the adjacent Kara Sea shelf in September 2011 and in August 2014. The spatial and seasonal differences in the phytoplankton structure were analyzed in connection with ice melting and changes in the temperature, salinity, and biogenic regime. Four 4 zones were defined: the Kara Sea shelf, the upper part of the St. Anna Trough slope, the lower part of the St. Anna Trough slope, and its deep part. It was shown that over the Kara Sea shelf where riverine runoff influence was observed, the phytoplankton community differs from the community of the St. Anna Trough in both investigated periods: in September and August. Rearrangement of the phytoplankton community was observed in the frontal zone associated with the upper part of the slope in September of 2011. The main features of this rearrangement were a change in dominant species composition and a 1.5–2-fold increase in the number and biomass of algae. Over the lower part of the slope and deep area of the St. Anna Trough in August 2014 and September 2011, the phytoplankton community was at different successive stages: in August, at the late spring and summer stage, and in September, at the summer–autumn stage.