## 4 Discussion  
Based on the proposed methodology, using the parameter of stable isotopes \(\delta^{18}\)O, calculated results of annual cycles of nutrient consumption and primary production in various areas of the Barents Sea, as well as the distribution of these values over the entire sea area, were obtained. Verification of the results for direct phytoplankton measurements and data calculated by us showed high convergence. Verification of the results for the calculation of primary production with data presented by other methods and other teams of authors also gave good convergence values. Some regularities in the dynamics of the consumption of nutrients and primary production both in the annual cycle and in the sea are revealed:  
* The value of the total consumption of nitrogen-nitrate in the entire water area of the eastern part of the sea in the summer, is at the level of the total consumption of this element in the process of photosynthesis (90-95%). That is, the almost complete consumption of mineral nitrogen in this part of the sea is the limiting factor in the development of the photosynthesis process. In the western part of the sea, in waters that are composed of the maximum incoming Atlantic waters [52], the values of nitrogen consumption are much lower and are in the range from 40 to 70%, although the values of primary production in these waters are a maximum. * The distribution of silicon consumption in the southern and central parts of the sea also tends to increase from west to east in the range of 30 to 60%. In the northern part of the sea, between the Svalbard and Franz Josef Land archipelagos, silicon can be a limiting factor in the development of the photosynthesis process. * Throughout the Barents Sea, phosphate phosphorus is not a limiting factor in the development of the photosynthesis process. The consumption of this element increases from west to east from 40 to 70%. * According to the largest values of primary production in the Barents Sea in the summer-early autumn period, an area with the highest average values of this value (NCP\({}_{\rm Si}\) > 150 g C m\({}^{-2}\)) was identified, which is confined to the water area of the Medvezhinsky-Spitsbergen shallow water and amounts to 152 \(\pm\) 36 g C m\({}^{-2}\), with maximum values up to 190 g C m\({}^{-2}\), although the NCP\({}_{\rm N}\) values in this area are not the highest (58 \(\pm\) 9 g C m\({}^{-2}\)). * Areas with relatively high values of primary production (NCP\({}_{\rm Si}\) > 100 g C m\({}^{-2}\)) include the area in the southwestern part of the sea, the area in the southeast of the sea, as well as the area adjacent to the Franz Josef Land archipelago from the south. The highest NCP\({}_{\rm N}\) values are observed in the southwestern part of the sea and amount to 73 \(\pm\) 7 g C m\({}^{-2}\) with an average NCP\({}_{\rm Si}\) value of 103 \(\pm\) 11 g C m\({}^{-2}\). * Areas with relatively low PP values (NCP\({}_{\rm Si}\) < 100 g C m\({}^{-2}\)) include areas on the northern border of the sea between the Spitsbergen archipelagos and Franz Josef Land and the area adjacent to the coast of the Kola Peninsula and extending in the west from the Varanger fjord to the throat of the White sea. The isotope parameter \(\delta^{18}\)O (\(\delta\)D) has unique conservative properties. It does not depend on chemical-biological processes and is an ideal tracer for balance estimates. The use of this parameter makes it possible to solve one of the main problems in the assessment of primary production using changes in the concentration of the biogenic element--to determine the starting point, i.e., the maximum concentration of a nutrient before the photosynthesis process starts. Moreover, this level of concentration can change during the year when one water is replaced by another, which can also be taken into account when using this parameter.