Black stratification

Seasonal shifts at mid-latitudes in the standing stocks of nutrients, phytoplankton, and the heterotrophic consumer community of bacteria, protozoa, and zooplankton. Also shown are seasonal changes in density stratification of the mixed layer. Source From Black, J. A. (1986). Oceans and Coasts, Wm. C. Brown Publishers, p. 143. 

Few studies aimed at understanding the effects of pressure on metabolism in fish have been performed in the Black Sea or Sea of Azov because no distinct stratification was found in the distribution of water animals there. The Sea of Azov is saucer-like, its maximum depth being only 15 m, and in the Black Sea the oxygenated water layer extends only to 150 m depth. However, Emeretli (1996) has shown that activity of lactate dehydrogenase in the liver increases 2-10 times in scorpion fish and annular bream placed in a barorespirometer (designed by A. Stolbov) and sunk to a depth of 300 m. This response seems to be peculiar to shallow-water species (Hochachka and Somero, 1984). 

Increase in the input of the organic matter and nutrients into the Black Sea causes increase of total phytoplankton biomass. In summer due to formation of the temperature, salinity and density stratification and algal blooms, decay of dead phytoplankton leads, in turn, to the oxygen lack and near-bottom hypoxia [9]. These processes have to consider as the consequence of anthropogenic eutrophication of the sea [9]. 

Storm surges. These significant nonperiodical sea level oscillations are caused by coastal winds. In so doing, their range and duration depend on numerous factors such as the time of forcing, the wind direction and speed, the outlines of the coastline, the shelf depth, and the water stratification. The most complete characteristics of the storm surges in the Black Sea are presented in [1,11]. 

In [48], it was shown that, in order to simulate the cold intermediate layer of the Black Sea (see [3]), one should take into account the dependence of the vertical turbulent mixing coefficient on the density stratification of the waters. In this case, the optimal coefficients in the well-known formula by Munk-Anderson for the Black Sea occurred to be an order of magnitude lower than those for the World Ocean. 

Bulgakov SN, Demyshev SG, Korotaev GK (1992) Modelling of the Black Sea circulation and water stratification (review). In Problems of the Black Sea. MHI UAS, Sebastopol, p 34... 

The evolution of the Black Sea anoxic zone is closely connected with the evolution of its stratification pattern, presently characterized by the existence of a strong pycnocline separating the upper freshwater-influenced surface layer, with a salinity of 17.5-18.5%o, and the deep water mass below ca. 150-200 m, with a salinity of 22.3%o at the bottom. Models for evolving Black Sea salinity after the opening of Bosporus agree that salinity in bottom waters reached 90% of present-day values about 3000 years after the Bosporus opening [14-17]. 

Satellite monitoring of the Black Sea performed during the past decade showed that the seasonal changes in the chlorophyll concentrations in the deep-water regions of the sea featured a distinct minimum in the summer and a maximum in the autumn-winter period. This kind of seasonal change is characteristic of subtropical seas, in which the summertime stratification restricts the nutrient supply and phytoplankton growth. The Black Sea, because of its extreme haline stratification, may be referred to the same type. 

Johonnott [314] explained stratification with alternating molecular forces of attraction and repulsion when a black film thins. Later, Keuskamp and Lyklema [352] pointed out that this phenomenon is caused by oscillation in the Gibbs free energy of the film when its thickness is changed. Two theories have emerged to account for these oscillations in the free... 

At large surfactant concentrations emulsion films as well as foam films exhibit a layer-by-layer thinning (stratification) and metastable black films are formed [31,347,512], Such a behaviour has been reported for hydrocarbon films obtained from solutions of lecithin in either benzene or a mixture of chloroform and decane at concentration higher than 0.6-0.8% as well as in films from oxidised cholesterol in decane [31,512]. Manev et. al. [347] have reported stratification of O/W type emulsion films, toluene being added as a disperse phase, occurring within a surfactant (NaDoS) concentration range of 0.017-0.14 mol dm 3. The number of metastable states was 5-6. Compared to foam films of analogous composition, the respective emulsion films were thicker, due to the weaker intermolecular attraction and the stratification occurred at lower surfactant concentrations. 

The test values in a healthy population used to derive a conventional reference interval are subject to the variety of influences including endogenous, exogenous, genetic or ethnic, and laboratory factors discussed above. The statistical approach used to calculate the interval also has considerable influence on the derived reference interval (see Chapter 16). No individual has test results that would span the entire reference interval. Indeed all the results within a healthy individual typically encompass only a small part of most reference intervals. Stratification into more appropriate intervals for subpopulations is sometimes required. The most typical stratifications are based on sex and age. Sinton et al have advocated that separate reference intervals are justified when the difference between the means of the potentially different populations (e.g., men and women or blacks and whites) is greater than 25% of the 95% reference interval of the entire population. An alternative approach to define whether stratification is appropriate is that of Harris and Boyd, which involves calculation of the standard deviations of all of the results from each of the potentially different populations and if the standard deviation of one is more than 1,5 times another stratification is justified. ... 

The experimental observations show that stratification is always observed when spherical colloidal particles are present in the film at a sufficiently high volume fraction therefore, a realistic explanation can be that the stepwise transitions are manifestations of the oscillatory structural forces. The role of the hard spheres this time is played by the colloidal particles rather than by the solvent molecules. The mechanism of stratification was studied theoretically in Reference 346, where the appearance and expansion of black spots in the stratifying films were described as being a process of condensation of vacancies in a colloid crystal of ordered micelles within the film. 

Since Sweden is more densely populated in die south, more possible pollutants are handled in that part. The deposidon of long-range transported pollutants is also higher in the south. This is die reason why we have chosen to have a stratification with 60 % of the lakes in the south of Sweden (die black area in Figure 2.1.7). 

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