статья в журнале

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PHYSICAL OCEANOGRAPHY

ISSN:0928-5105
eSSN:1573-160X

2022

10.22449/1573-160X-2022-1-83-97

Purpose. The paper is aimed to analyze (i) peculiarities of the oxygen content and distribution in the Black Sea waters and (ii) the ratio of the observed changes in the oxygen distribution, the total primary production level and changes in the cold intermediate layer ventilation. Methods and Results. The expedition data (2015-2019) as well as the data array (1980-2013) from the Oceanographic Data Bank of Marine Hydrophysical Institute, RAS, were used to analyze the oxygen content. The data for the deep part of the Black Sea (exceeding the 200 m depth) were selected. To analyze the primary production values, the shipboard fluorometric measurements of the chlorophyll a concentrations (1980-2001), and also the surface chlorophyll a concentrations derived from the SeaWiFS and MODIS-Aqua color scanners remote sensing (1998-2019) were utilized. The primary production was calculated using the regression equations in the form y = a + bx that bound up the primary production in the water column with the surface chlorophyll concentration. The calculated data reveal a significant increase in the annual primary production level (to 400 g C/m(2).year) in the first half of the 1980s, then it declined on the average to similar to 140 g C/m(2) year from 1985 to 1995, and it remains at the level of similar to 100 g C/m(2) year from 1998 up to the present time. These variations in the primary production values correspond to the observed changes in the vertical distribution of nitrate and an increase in the temperature of the cold intermediate layer core, resulting in a decrease of the oxygen concentration in the deep oxic layers. Conclusions. An increase in temperature in the upper layers of the sea and a reduction of the winter convective mixing intensity resulted in a decrease in the oxygen supply to all layers of the aerobic zone of the Black Sea. The lowest oxygen content recorded for the whole period of 1980-2019 was revealed in 2010. At the same time, dystrophication process drove the Black Sea system to its natural state, when the oxygen content dynamics depended mainly on the intensity of physical ventilation.

oxygen, oxygen concentration, eutrophication, primary production, cold intermediate layer, Black Sea

2022-04-11 10:45:39