## 4 Discussion  
The deserts of the Earth are huge sources of dust [48], the maximum influx of dust occurs in winter and spring, and its compositions (including nutrients) vary between seasons [49]. The presence and quantity of the main nutrients (inorganic nitrogen and phosphorus, as well as silicon) along with the light intensity determines the growth and development of various phytoplankton species in marine ecosystems. Many authors have studied the influence of dust aerosols on the characteristics of marine ecosystems. It is considered that in comparison with the input of nutrients from the bottom layers nutrients-enriched, as well as in a result of water mixing, the atmospheric source of these elements is not so significant [22]. At the same time, it is noted that the nutrient load added as a result of atmospheric deposition at a certain time can be very important to primary production [22; 49; 50; 51]. However, most papers are dedicated to the influence of dust aerosols on the Mediterranean Sea. The influence of the nutrients transfer contained in the dust aerosol on the Black Sea surface layer remains insufficiently studied. The aim of this work was to study the patterns and features of dust deposition of the Sahara and Syria with high nutrients concentrations in the Black Sea region, as well as its influence on the dynamics and distribution of the concentration of chlorophyll-A in the surface layer of the Black Sea. In our work, we showed the change in the chlorophyll-A in the surface layer of the Black Sea waters after precipitation containing high concentrations of inorganic nitrogen, phosphorus, and silicon. At the same time, we excluded the influence of upwelling on this change. In total, for the period 2010-2019, it was collected and processed about 400 atmospheric precipitations samples. We also collected and analyzed samples of seawater after precipitations. In these samples, the concentration of inorganic nitrogen, phosphorus, and silicon has been measured. Our results demonstrate that in some cases dust transport can be one of the important source of nutrients (inorganic nitrogen, phosphorus, and silicon) for the surface layer of the Black Sea. Under certain conditions, influx of nutrients via atmospheric depositions can result in an increase of chlorophyll-A concentration in the surface layer of the Black Sea (Figures 3 and 6). This increase is observed in a few days after precipitations and its value depends on the concentration of nutrients in the atmospheric depositions and underlying biogeochemical conditions in the water column [52]: concentration of chlorophyll-A in the surface layer before dust storm and atmospheric depositions, etc. Our data are in agreement with some results obtained by other researchers for different areas (Mediterranean Sea, Arctic region, etc.). For example, results [53] demonstrated that a single deposition event is enough to induce changes in the microbial food web up to zooplankton. Refs. [22; 52] showed that atmospheric phosphorus can contribute \(\sim\)1% of primary production in the NW Mediterranean. However, occasional events may contribute about 30-50% of annual new production. Ref. [50] confirmed an increase of chlorophyll-A concentration in the Mediterranean Sea in April 2015 by 59% a week after precipitation. According to our data obtained during this research, concentration of chlorophyll-A in the surface layer of the Black Sea can increase up to 11-36% after atmospheric depositions (Figures 4 and 8). In spring or in conditions of stratification, this could indicate that dust deposition would make the system more productive. In the next few days after precipitations or dust storm, the concentration of chlorophyll-a decreases, reaching background values. Ref. [52] also considered the response of inorganic phosphorus concentration in the surface water layer on the atmospheric impact. It is shown that depending on productivity, different regions respond differently.