A. V. Tolstikov

Multidisciplinary studies in Onega Bay of the White Sea and the estuary of the Onega River during the summer period

The distribution of the temperature and salinity, current velocities, suspended particulate matter, bottom sediments, bottom morphology, and planktonic and benthic organisms during the summer period are studied in the estuary of the large Onega River and the coastal areas of Onega Bay (White Sea) influenced by interacting marine and riverine factors.

Manifestation of marine and riverine factors in the tide and ebb phases along the white sea coasts of different configuration

The peculiarities of the distributional patterns of the water temperature, salinity, current velocities, particulate matter concentration, bottom contour, and zooplankton abundance were studied in relation to the marine-riverine interactions and tide/ebb phases for coast lines of different configurations in the White Sea during the cruises of the R/V Ekolog (August of 2006 and 2007). A significant difference in the manifestation of the combined effect of the marine and riverine impacts (the estuarine concave relief) and only the marine impact (the open-sea straight-line portion) was observed, which results in both variations in the sea water level and the distributional patterns of the suspended matter and the zooplankton.

Multidisciplinary Investigations of the White Sea during the Period of the Summer Low Water in 2009 Onboard the R/V Ekolog

630 Multidisciplinary expedition onboard the R/V Ekolog was carried out in the White Sea during the period of the summer low water on July 5–17, 2009. The expedition was organized by the P.P. Shirshov Institute of Oceanology of the Russian Academy of Sciences and the Institute of Water Problems of the North of the Karelian Research Center of the Russian Academy of Sciences. The studies were carried out in the framework of the White Sea System project (the project leader is Academician A.P. Lisitzin) [5], and the project aimed at studies of the natural processes in the tidal shore zones of the White Sea (the project leaders are Corresponding Member of the Russian Academy of Sciences N.N. Filatov and Correspond ing Member of the Russian Academy of Sciences Yu.S. Dolotov) [2, 8]. Researchers from different institutes participated in this expedition: the P.P. Shir shov Institute of Oceanology (including its North western Branch), the Institute of Water Problems of the North of Karelian Research Center of RAS, the Federal State Unitarian Research and Production Company for Geological Sea Surveys (SEVMOR GEO), the D.V. Skobeltsyn Institute of Nuclear Phys ics (SINP) of Moscow State University, the Sergo Ordzhonikidze Moscow State Geological Prospecting University, and the Zoological Institute. The route of the cruise is presented in Fig. 1. The expedition was aimed at multidisciplinary stud ies of the natural environment of the White Sea during the period of the summer low water with special refer ence to most of the oceanological fields (the physics, chemistry, biology, and geology of the ocean) and the seasonal and spatial dynamics of numerous environ mental parameters (the 4 D approach). The objectives of the expedition included the fol lowing: (1) studying the geochemical processes at the river–sea boundary (the marginal filters of the Kem’ River and the Zolotitsa River inflowing to Onega Bay of the White Sea); (2) the maximal incorporation of the satellite data into the analysis (when plotting the maps of the sus pended matter, chlorophyll, and temperature distribu tion patterns); (3) onboard sampling simultaneously with the ves sel’s traversing to verify the satellite data (the chloro phyll and temperature); (4) hydrophysical profiling at the stations using a multiparameter 90M CTD (Sea & Sun), including the temperature, the salinity, the water turbidity, and some other measurements; (5) Secchi depth measurements; (6) water sampling at the surface and from standard water layers with the filtration of the water through glass fiber filters and Nucleopore membrane filters for Multidisciplinary Investigations of the White Sea during the Period of the Summer Low Water in 2009 Onboard the R/V Ekolog

Mean multiannual temperature regime of the surface water layer in the near-shore regions of the White Sea

The mean multiannual temperature regime of the surface water layer in the near-shore regions of the White Sea is analyzed from the data obtained at the VNIIGMI-MTsD (Obninsk). A function describing the seasonal temperature trend in the surface layer was found by the method previously used for an analysis of the Onega and Ladoga lakes. The method is based on the nonlinear approximation of the field observations by a function composed of a combination of exponents with coefficients to be calculated. Explicit seasonal dependences of the mean temperature of the surface water layer in the White Sea were obtained for nine near-shore stations. The root-mean-square deviations of the measured values of the water temperature were estimated.

Phytoplankton structure in the White Sea after summer bloom: Spatial variability in relation to hydrophysical conditions

The species composition and phytoplankton biomass, concentrations of chlorophyll “a” (Chl) and nutrients, concurrent hydrophysical conditions were studied in the south part of the White Sea in July 10–15, 2012 during chlorophyll “a” decrease after summer peak. The water column stability varied, the concentration of dissolved silicon in upper mixed layer was closed to the range favorable for diatoms with exception of areas of intensive tide mixing and areas influenced by waters of Severnaya Dvina River. In surface layer the dinoflagellates dominated excepting of areas with intensive tide mixing where diatoms prevailed. Diatoms provided major contribution to biomass in different stations above, in and under pycnocline and in deep waters out of photic zone. Structural analysis has revealed three phytoplankton communities that corresponded to different depths: communities of photic zone, intermediate and deep layers. Extension of layers inhabited by different communities depended on water column stability and on genesis of water masses. Integrated values of phytoplankton biomass and Chl varied from 250 to 1188 mg С/m2, and from 22 to 51 mg/m2, correspondently.

Studies of the White Sea System from onboard the R/V Ekolog in July 2010

1074 A complex expedition onboard the R/V Ekolog was performed in the White Sea on July 18–29, 2010. The expedition was organized by the Shirshov Institute of Oceanology of the Russian Academy of Sciences and by the Institute of Water Problems of the North of the Karelian Research Center of the Russian Academy of Sciences. The studies were performed in the frame� work of the project System of the White Sea (the project leader was Academician A.P. Lisitzyn) [2], and the project was aimed at studies of the natural pro� cesses’ peculiarities in the tidal shore zones of the White Sea (the project leaders were Corresponding Member of the Russian Academy of Sciences N.N. Filatov and Corresponding Member of the Russian Academy of Sciences Yu.S. Dolotov) [1]. Researchers from the Shirshov Institute of Oceanology (including the Northwestern Branch) and the Institute of Water Prob� lems of the North participated in this expedition. The cruise leg is presented in the figure. The expedition was aimed at multidisciplinary stud� ies of the natural environment of the White Sea during the summer period with special reference to most of the oceanologic fields (the physics, chemistry, biology, and geology of the ocean) and the seasonal and spatial dynamics of numerous environmental parameters (the 4�D approach). The objectives of the expedition included the fol� lowing:

Spatial Distribution of the Phytoplankton in the White Sea during Atypical Domination of Dinoflagellates (July 2009)

The species composition and biomass of phytoplankton, concentrations of chlorophyll a (Chl a) and nutrients, and accompanying hydrophysical conditions have been studied in the White Sea on July 6–11, 2009. The temperature of the surface water layer was lower than the multiyear average in July. Dinoflagellates dominated in the entire studied area; this was not the typical event for July. We suggest that domination of dinoflagellates was caused by low water temperature, when the nutrient regeneration rate was insufficient to support diatom growth. The abundance of microalgae and the structure of the phytoplankton community depended on the water structure. Variations in the phytoplankton community structure were caused not by substitution of specific species but rather by variability of the abundance of a single species, Heterocapsa triquetra. The highest phytoplankton biomass has been recorded in weakly stratified waters, where tidal mixing supplied the income of inorganic nutrients. The income of nutrients to the photic layer was limited in the stratified waters of Dvina Bay during the summer low-water period, so the phytoplankton abundance was low. We suggest that the lens of surface desalinated water presumably originated from the outlet of the Dvina River was registered in the central part of the White Sea.