The search for target values of quality indices for bioindicators of the ecological state and environmental factors: Case study of water bodies of the Don river

The possible use of quantitative characteristics of phytoplankton species diversity for water quality bioindication and for the search for ecologically admissible levels of abiotic factors is examined. Retrospective materials on the Don basin obtained from data of state environmental monitoring of freshwater in Russia are used. The effect produced on the characteristics by the diversity of errors in the calculation of the numbers of phytoplankton cells, the procedure used to assess rank distribution parameters, the adequacy of formal models of rank distributions, the relationship between the uniformity of rank distributions and species diversity, sampling season, water body type, and the geographic location of sampling site is analyzed. The obtained diversity characteristics are in agreement with the available monitoring data. Boundaries of the examined characteristics, corresponding to the well-being ranges of phytoplankton communities, were found. The ecologically admissible levels were calculated for the major abiotic factors.     

Seasonal variability of the hydrologic-and-acoustic parameters on the Black Sea shelf off the South Crimea coast

Usingin situ temperature and salinity observations from the Marine Hydrophysical Institute's oceanographic data set, regularities of the formation of structure and seasonal variability of the calculated sound speed field, as well as elements of the latter's vertical stratification in the South Crimea shelf area, have been studied. The ray approximation is applied to consider the influence of seasonal variations of the vertical hydrologic-and-acoustic structure on the propagation of sound in the sea. Translated by Vladimir A. Puchkin.     

Intrayear Variability of Geostrophic Zonal Currents in the Tropical Zone of the South Atlantic

On the basis of the results of calculation and analysis of the characteristics of space variability of the geostrophic component of large-scale zonal currents in the tropical zone of the South Atlantic, its intrayear oscillations, and the components of tangential wind stresses, we establish the regularities of seasonal variability of the system of gradient currents on the ocean surface depending on wind conditions. We describe the specific features of seasonal meridional fluctuations of the midstreams of the geostrophic component of zonal large-scale currents and the intrayear variations of their velocity.     

Synoptic variability of the acoustic characteristics in tropical Atlantic waters

Synoptic variability of the sound speed and parameters of the SOFAR channel in the tropical Atlantic are considered. The synoptic component of the temporal and spatial dispersions of sound speed is singled out. The synoptic processes are shown to essentially affect the vertical hydroacoustic structure on a 1-month scale. It has been found that synoptic variations in the sound speed field penetrate as far as the SOFAR channel axis and deform it considerably.Translated by V. Puchkin.     

The major objectives and results of investigations carried out during cruise 41 of R/V Akademik Vernadsky

The objectives of cruise 41 of R/VAkademik Vernadsky and the data provided on the RAZREZY project are reported.Translated by V. Puchkin.     

Optimal statistical estimates of the vertical current velocity in the north-western Black Sea

The paper discusses a method for the statistical evaluation of the vertical current velocity componentV _z(z) using data provided by profilers. The calculation of theV _z(z) profiles involves the determination of the root-mean-square deviation of the error of determination of the vetical current velocity component at each level and the RMS deviation of the sample statistical variability of this quantity's estimates. ProfilesV _z(z) have been computed for the north-western Black Sea using three surveys, with the involvement of an OLT profiler. The computations have shownV _z(z) to have a two-layer structure, with zero being crossed in the main pycnocline. Such structure of the current velocity vertical component is consistent with the hydrodynamic model of the field of currents induced by buoyancy fluxes through the lateral boundaries of the basin. The availability of the zero values of the vertical current velocity in the pycnocline yields a tool for gaining insight into the mechanism controlling the emergence of the oxic/anoxic interface and areas with sharp vertical gradients of chemical and hydro-optical characteristics. Translated by Vladimir A. Puchkin.     

The seawater structure of the Guyana Current and the North Equatorial Countercurrent in February–April 1990

Novel data on the kinematic and thermohaline structures of waters in the Guyana Current and the North Equatorial Countercurrent (NECC) in the winter-spring period have been obtained based on the complex hydrophysical research carried out within the economic zones of Brazil, Surinam, Barbados, and the adjacent regions. The transports of current are estimated from the results of instrumental measurements and geostrophic computations. The thermohaline characteristics of water masses are given. A bifurcation of the Guyana Current at 54–55° W is described. The results obtained are compared with those of previous research and climatic data. It is shown that the intense manifestation of the NECC at the surface is anomalous at the end of winter and early in spring.Translated by Mikhail M. Trufanov.     

Seasonal deformation of the North Equatorial Countercurrent in the Atlantic Ocean

The geostrophic circulation of active and intermediate layers in the north Tropical Atlantic is analysed on the basis of data collected in the transatlantic study area in 1986–1987. Its seasonal features are also found. Quasi-steady eddy formations and their relation to the bottom topography are considered for the intermediate region. The influence of these formations on the kinematics of large-scale currents in this layer is substantiated. Structures of large-scale tropical cyclonic and anticyclonic eddy formations are specified. A strategy for further studies in the Tropical Atlantic is suggested.Translated by Mikhail M. Trufanov.     

Generation of Upwelling near the Pacific Coast of Mexico

In a series of numerical experiments, we simulate the process of generation of coastal upwelling induced by the winds of various directions in the central part of the Pacific Coast of Mexico (18–24°N, 103– 107°W). The numerical nonlinear multilevel model [see E. N. Mikhailova, I. M. Semenyuk, and N. B. Shapiro, “ Modeling of the variability of hydrophysical fields in the Tropical Atlantic,” Izv. Akad. Nauk SSSR, Fiz. Atmosf. Okean., 27, No. 10, 1139–1148 (1991)] is adapted to the region of investigations with 9-km space resolution by specifying the conditions of flow through the open lateral boundaries. The results of numerical experiments demonstrate that the NW, N, NE, and E winds are especially favorable for the generation of intense upwelling.__________Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 32–41, January–February, 2005.     

Peculiarities of the currents field in the north-western part of the Black Sea

On the basis of the results derived by theoretical analysis [1] and laboratory physical modelling [2] of the circulation seawater and stratification, induced by buoyancy fluxes, the suggestion has been made that, possibly, the Black Sea currents system is three-layered. It has been supposed that an anticyclonic current flows in the basin. To verify this deduction, the data from MHI's archived dataset have been treated, and results from twoad hoc expeditions are submitted here. Analysis of the vertical structure of currents, based on thein situ velocity measurements, using various means and calculations of the geostrophic circulation, has confirmed that a flow with the theoretically predicted parameters may exist in the Black Sea. Translated by Vladimir A. Puchkin.