S. A. Mosharov

Distribution of the primary production and chlorophyll a 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).

Structure of the phytoplankton communities and primary production in the Ob River estuary and over the adjacent Kara Sea shelf

The material was collected in the Ob River estuary and over the adjacent shallow Kara Sea shelf between 71°14′0 and 75°33′0N at the end of September 2007. Latitudinal zoning in the phytoplankton distribution was demonstrated; this zoning was determined by the changes in the salinity and concentration of nutrients. Characteristic of the phytocenosis in the southern desalinated zone composed of freshwater species of diatom and green algae were the high population density (1.5 × 106 cells/l), biomass (210 μgC/l), chlorophyll concentration (4.5 μg/l), and uniform distribution in the water column. High primary production (∼40 μgC/l/day) was recorded in the upper 1.5-m layer. The estuarine frontal zone located to the north contained a halocline at a depth of 3–5 m. Freshwater species with low population density (2.5 × 105 cells/l), biomass (24 μgC/l), and chlorophyll concentration (1.5 μg/l) dominated above the halocline. Marine diatom algae, dinoflagellates, and autotrophic flagellates formed a considerable part of the phytocenosis below the halocline; the community characteristics were twofold lower as compared with the upper layer. The maximal values of the primary production (∼10 μgC/l per day) were recorded in the upper 1.5-m layer. The phytocenosis in the seaward zone was formed by marine alga species and was considerably poorer as compared with the frontal zone. The assimilation numbers at the end of the vegetation season in the overall studied area were low, amounting to 0.4–1.0 μgC/μgChl/h in the upper layer and 0.03–0.1 μgC/μgChl/h under the pycnocline.

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.The average primary production was 112.6, 58.5, and 28.7 mg C m−2 day−1, and the bacterial production was 12.8, 48.9, and 81.6 mg C m−2 day−1 along the Yamal Peninsula, the St. Anna Trough, and Ob Bay, respectively. The average bacterial carbon demand was 34.6, 134.5, and 220.4 mg C m−2 day−1 for these regions, respectively. The data obtained lead us to conclude that the phytoplankton-synthesized organic matter is generally insufficient to satisfy the bacterial carbon demand and may be completely assimilated via the heterotrophic processes in the marine ecosystems. Therefore, the bacterial activity and, consequently, the amount of the synthesized biomass (i.e., the production) both depend directly on the phytoplankton’s condition and activity. We consider these relationships to be characteristics of the Kara Sea’s biota.

Spatial Variability of the Primary Production and Chlorophyll a 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 (PPint) for the water column in this area was developed based on the data on the surface chlorophyll (Chls) 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 PPint (<100 mg C/m2 per day) and Chls (0.08–0.20 mg/m3) in October–November. Low values of the Chls 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 Chls concentration of more than 1 mg/m3 in mid-November in this area and the Subantarctic waters.

Vertical distribution of primary production and chlorophyll a in the Kara Sea

On the basis of data obtained during three ecosystem expeditions in the Kara Sea, the vertical variability of the primary production (PP) and chlorophyll a (Chl) in autumn was studied. The Chl maximum was detected mainly on the surface (Chl0). A homogenous Chl distribution in the euphotic layer (1% photo-synthetically available radiation) and a nearly linear decrease in the Chl concentration below this layer were observed in waters with Chl0 values of 0.1–0.5 mg/m3. In waters with Chl0 > 0.5 mg/m3, the Chl concentration in the studied layer decreased linearly or exponentially. The subsurface Chl maximum (SCM) was registered weekly and was detected mostly in waters with a Chl0 content of 0.1–0.5 mg/m3. The SCM formation in the Kara Sea was consistent with the general patterns for the World Ocean. Water-column stability, the content of biogenic elements, and the level of subsurface irradiance had an approximately equal effect on SCM formation. The contribution of the SCM to the depth-integrated PP varied from 1 to 27%. The parameterization of vertical profiles of Chl was performed in order to be used in depth-integrated PP models. The Chl maximum on the surface and the negligible SCM facilitate the estimation of depth-integrated PP on the basis of satellite data and the use of vertical-resolution models.

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 2009–2010 and the spring of 2010 on the basis of field measurements. In October–November, 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–January 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.

Interannual Variability of the Zooplankton on the Shelf of the Northeastern Black Sea in the Autumn Period

The variability of the mesozooplankton stock in the shelf pelagic communities was studied in the late summer and autumn of 2006–2008. The plankton community’s structure and distribution were described for the shoreward transect (Gelendzhik city vicinity). The indirect and direct effect of the ctenophores Mnemiopsis leidyi and Beroe ovata on the mesozooplankton community was studied. The long-term changes in the meso- and macroplankton communities of the Black Sea were analyzed for the period of 2001–2008. The effects of the climatic factors, the water mass circulation, and the factors’ interplay on the mesozooplankton dynamics were assessed. Despite the wide range of the environmental conditions, the stock biomass of Mnemiopsis leidyi appeared to be quite stable within the studied period.

Peculiarities of the primary production process in the Kara Sea at the end of the vegetation season

Research was implemented from September 15 through October 4, 2011 in the Kara Sea along transects located southeastwards Novaya Zemlya, in the St. Anna Trough, the Yenisei River estuary, and the adjacent shelf. The concentration of chlorophyll a was the highest in the photic zone (0.05–2.30 mg/m3, on average, 0.80 ± 0.37 mg/m3). The maximal concentration of Chl a at most of the stations located in the water layer of 7–30 m. Integral primary production in the water column varied from 3.0 to 151.0 mg C/m2 per day, on average, 37.2 ± 36.6 mg C/m2 per day. The maximal rate of primary production at most of the stations has been observed for the surface layer of the water column. Within the upper mixed water layer, relative primary production was from 31 to 100% (on average, 77 ± 20%). The most productive zone was the waters along Yenisei transect. In the estuary and at the adjacent shelf, primary production was 50 mg C/m2 per day, exceeding the range observed for other areas by 1.5–2.0 times. The concentrations of silica and nitrogen together with light regime and water temperature were the major limiting factors affecting the primary production rate in the Kara Sea in autumn.

Evaluation of the influence of abiotic and biotic factors on primary production in the Kara Sea in autumn

A regression analysis of the parameters of primary production versus environmental factors was performed on the basis of data of three complex expeditions performed in the Kara Sea in September to October 1993, 2007, and 2011. The analysis of the dependence of the depth-integrated primary production (PPint) on the value of surface chlorophyll a (Chl0) and assimilation activity (ANm) showed that only 12% of the variability of the integrated PPint was determined by the variability of Chl0, whereas the correlation between PPint and ANm was strong (R2 = 0.635). Thus, in autumn, PPint values in the Kara Sea depended primarily on the activity of phytoplankton assimilation. At the end of the vegetative season, high (close to or above 1 mg/m3) Chl0 values did not reflect phytoplankton production within the entire photosynthetic layer, where organic matter was synthesized at a low rate. In turn, PPint and ANm depended primarily on the intensity of insolation and was weakly related to the content of dissolved forms of nitrogen and phosphorus. In autumn, at the end of the vegetative season, insolation apparently is the main factor in the determination of the formation of primary production in the Kara Sea.