Influence of Wind Direction on the Elemental Composition of Atmospheric Deposition on the Black Sea Coast of Sochi, Russia

This study investigated the influence of wind direction on the elemental composition of rainwater along the Black Sea coast near Sochi, Russia. Rainwater samples were collected from both a densely populated area and a park zone with minimal anthropogenic influence to determine their cation-anion composition using traditional methods and quantify the content of 70 elements using inductively coupled plasma (ICP) spectrometry. Notably, the sampling period encompassed precipitation events with varying wind directions, facilitating the differentiation between elements of terrestrial origin, likely associated with atmospheric dust, and those with a predominantly marine source. Rainwater influenced by northeasterly winds exhibited enrichment in rare earth elements (REEs), Zn, Ni, Pb, Mn, Cu, Al, Rb, As, Bi, and Tl. This elemental signature mirrored the geochemical composition of the region's clay-rich rocks and diverse mineral zones, suggesting a local terrestrial source. In contrast, a shift to southeasterly winds transporting air masses from the sea resulted in a dominance of elements indicative of oceanic origins, such as Na > Mg > S > Sr > Cl > Br > K. The subsequent analysis of solid atmospheric deposition, which characterizes the composition of the atmosphere under conditions of a south-easterly wind direction in winter, corroborated the previously obtained data. The elemental composition, Cl > Mg > Na > Sr > Ca > K > Ce > Mn > S, was found to be consistent with a marine source influence during the winter period. These findings led to the development of a novel geochemical indicator of marine origin (GIM), calculated as the ratio of marine-associated elements to terrestrial elements (GIM = Mtotal × ∑ Na Mg S Sr Cl Br K / ∑ REEs Zn Ni Pb Mn Cu Al Rb As Bi Tl). GIM values displayed significant variation, ranging from 1456 for rainwater influenced by continental sources to 2579 for rainwater with a strong marine signature. This substantial variation in GIM underscores its potential as a valuable tool for estimating the relative contributions of oceanic and terrestrial sources to the overall elemental composition of rainwater in the studied region.