The plankton community in Norwegian coastal waters—abundance, composition, spatial distribution and diel variation

The purpose of the present study was to explore the composition and variation of the pico-, nano- and micro-plankton communities in Norwegian coastal waters and Skagerrak, and the co-occurrence of bacteria and viruses. Samples were collected along three cruise transects from Jæren, Lista and Oksøy on the south coast of Norway and into the North Sea and Skagerrak. We also followed a drifting buoy for 55 h in Skagerrak in order to observe diel variations. Satellite ocean color images (SeaWiFS) of the chlorophyll a (chl a) distribution compared favorably to in situ measurements in open waters, while closer to the shore remote sensing chl a data was overestimated compared to the in situ data. Using light microscopy, we identified 49 micro- and 15 nanoplankton sized phototrophic forms as well as 40 micro- and 12 nanoplankton sized heterotrophic forms. The only picoeukaryote (0.2-2.0 μm) we identified was Resultor micron (Pedinophyceae). Along the transects a significant variation in the distribution and abundance of different plankton forms were observed, with Synechococcus spp and autotrophic picoeukaryotes as the most notable examples. There was no correlation between viruses and chl a, but between viruses and bacteria, and between viruses and some of the phytoplankton groups, especially the picoeukaryotes. Moreover, there was a negative correlation between nutrients and small viruses (Low Fluorescent Viruses) but a positive correlation between nutrients and large viruses (High Fluorescent Viruses). The abundance of autotrophic picoplankton, bacteria and viruses showed a diel variation in surface waters with higher values around noon and late at night and lower values in the evening. Synechococcus spp were found at 20 m depth 25-45 nautical miles from shore apparently forming a bloom that stretched out for more than 100 nautical miles from Skagerrak and up the south west coast of Norway. The different methods used for assessing abundance, distribution and diversity of microorganisms yielded complementary information about the plankton community. Flow cytometry enabled us to map the distribution of the smaller phytoplankton forms, bacteria and viruses in more detail than has been possible before but detection and quantification of specific forms (genus or species) still requires taxonomic skills, molecular analysis or both.     

The scale factor in a Universe with dark energy

The solution of the Friedmann cosmological equations for the scale factor in a model of the Universe containing matter having the equation of state of dust and dark energy is considered. The equation-of-state parameter of the dark energy is taken to be an arbitrary constant w = ?1.006 ± 0.045, whose value is constrained by the current observational limits. An exact solution for the scale factor as a function of physical time and conformal time is obtained. Approximate solutions have been found for the entire admissible conformal time interval with an accuracy better than 1%, which exceeds the accuracy of the determined global parameters of our Universe. This is the first time an exact solution for the scale factor describing the evolution of the Universe in a unified way, beginning with the matter-dominated epoch and ending with the infinitely remote future, has been obtained.     

Principles of Pulsar Space Navigation

Astronomy Reports - The paper considers the principles of space navigation using pulsars observed in the radio range. The requirements for receiving equipment are outlined, a recommended pulsar...     

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.     

Relationships between the cell volume and the carbon content of bacteria

The bacterial biomass is an essential point in microbial ecology. The dry weight and carbon content of microorganisms are traditionally used for the calculation of the fluxes of carbon and energy in aquatic ecosystems. Since direct measurements of these parameters in natural conditions are rather difficult, a certain biomass-carbon converting factor is used, which is determined experimentally or by empirical calculations. However, the relationship between the cell volume and its dry weight (in particular, carbon) does not depend only on the cell size and the conditions of its growth but also on the fixation and staining methods used. We made an attempt to summarize all the present data on the relationships between the cell volume, its dry weight, and the carbon content. Thus, the principal goal of the present study was searching for a generally applicable or methodology-dependent converting factor for the bacterial biomass calculation. Thereto, all the data available were grouped according to the dye used, as well as to the methods of fixation and the dry weight determination. The data on the most frequent combinations of dies and fixatives are insufficient for precise calculations; therefore, we suggest a relationship generalized for different methods of carbon and cell volume recalculations and applicable for bacterial cells larger than 0.025 μm³, as fgC cell⁻¹ = 133.754 × V ^0.438.     

Some aspects of four-dimensional black hole solutions in gauss-bonnet extended string gravity

An internal singularity of a string four-dimensional black hole with second order curvature corrections is investigated. A restriction to a minimal size of a neutral black hole is obtained in the frame of the model considered. Vacuum polarization of the surrounding space-time caused by this minimal-size black hole is also discussed.     

Effects of gravitational microlensing of binary and multiple stars

The observation of microlensing events towards the Large Magellanic Cloud and Galactic Bulge discovers a new population of our Galaxy which is that of dark bodies with masses of the order of 0.1M . Astronomy has now a unique ability: one can use the microlensing as a space telescope with extremely high angular resolution. Here we discuss the opportunity of the application of this ability to observation of close binaries. Stars in a binary system move around their barycenter and as a result the apparent motion is modulated by binary motion. The light curve of this microlensing event becomes nonsymmetrical. If a binary has two stars with different spectral types, one can expect significant variation of color during microlensing effect. Accurate light curves for some typical binaries have been calculated and are presented here. The total fraction of binaries in our Galaxy is around 50%. Therefore one can expect half of the microlensing events to have nonsymmetrical and wavelength depending light curves which would indicate that background star is binary. Our opinion is that the absence of these light curves are due to some selection effect. This leads to an underestimation of the density of the dark body population in our Galaxy by a factor of about two.     

Bacterioplankton in the northeastern part of the Black Sea during the summer and autumn of 2005

On the basis of luminescent microscopy using a DAPI dye, the abundance, morphometric characteristics, and biomass of bacteria in the coastal waters off the northeastern part of the Black Sea in 2005 were considered. The material was collected in June, September, and October along the cross section from Golubaya Bay towards the open part of the sea. An analysis of the microorganism development level showed that the bacteria achieved their maximal abundance in September, amounting, in the closest near-shore area, to 2435 × 10³ cells/ml, or 276 mg/m³ of wet weight; the lowest values were characteristic of October. During all the survey periods, coccal forms were prevailing among the microorganisms; regardless of the season, their fraction was maximal at the coastal stations. The greatest prevalence of coccal forms was characteristic of October (83%). The average sizes of the bacterial cells in 2005 varied within 0.073–0.257 μm³. The highest values of the bacterial abundance and biomass, almost in all the cases, were found at coastal stations; with the distance from the coast, a decrease in the bacterioplankton abundance was observed. A comparison of methodically similar data on the concentration of bacteria (dying with acridine orange and DAPI) from 1985 till now shows a trend of the annual growth in the bacterial abundance.