Specific features of the vertical distribution of elements of the main biogenic cycles in waters of the Northwest shelf of the Black Sea

Abstract

551.465We study specific features of the vertical distribution of elements of the main biogenic cycle in the upper layers of waters on the northwest shelf of the Black Sea in spring and autumn and the correlation between the specific features of the vertical distributions of hydrochemical and hydrological characteristics. It is shown that the location of the halocline always specifies the location of the chemocline, whereas the effect of the thermocline on the distribution of hydrochemical characteristics is ambiguous. The vertical distribution of the hydrochemical parameters can be homogeneous in the presence of the seasonal thermocline. At the same time, in its absence, one may observe significant vertical gradients in the distributions of hydrochemical characteristics inside the upper mixed layer.In analyzing the vertical distributions of elements of the main biogenic cycle in the upper layers of the Black Sea, main attention of the researchers is traditionally focused on the behavior of concentrations in the course of transformation of the aerobic zone into the anaerobic zone. A detailed description of the biochemical processes running in this case between the isopycnic surfaces with σ t = 14.2 and σ t = 16.5 can be found in [1][2][3][4][5][6].Much less attention is given to the specific features of the vertical distribution of biogenic elements in shelf waters, although the problem of expected changes in the concentrations of biogenic elements in the course of motion from the surface to the cold intermediate layer is actually of the same level of complexity as the analysis of specific features of the vertical distributions of hydrochemical characteristics in the suboxic and hydrogensulfide zones. The field studies carried out in the shelf zone are, as a rule, restricted to taking samples on the surface and in the bottom layer.. However, by using this methodical approach, it is impossible to study specific features of the vertical distribution of stratified shelf waters containing the upper mixed layer (UML), the layer of seasonal thermocline, the upper boundary of the cold intermediate layer with σ t = 14.1-14.3, and the core of the cold intermediate layer with σ t = 14.5-14.6. The specific features of the vertical distributions of elements of the main biogenic cycle under the isopycnic surface σ t = 15.0 on the northwest shelf (NWS) in May 2004 and May 2007 are studied in [7,8].In the present work, we study the distributions of biogenic elements in the spring and autumn seasons in the upper 100-m layer of waters with high vertical resolution in the regions of the northwest shelf not subjected to the influence of river discharge and analyze the correlations between the specific features of the distributions of chemical and hydrological characteristics. Materials and MethodsFor the analysis of the vertical profiles of concentrations of biogenic elements, we use the data of three expeditions of the Marine Hydrophysical Institute of the Ukrainian Academy of Sciences for the last twelve years.Marine Hydrophysica...