Study of the Bottom Sediments Composition in the Volcanic Thermal–Seawater Mixing Zone

Mixing zones of natural waters are a contrasting geochemical barrier where the oxidation–reduction, acid–base, and temperature parameters vary. The presented report discusses the result of mixing the solutions of the Yuryeva River (Paramushir Island, Northern Kuril Islands) and waters of the Sea of Okhotsk. The Yuryeva River alone is one of the most abundant ultra-acidic rivers in the world. In 2023, comprehensive field studies were conducted at the island–sea boundary in the Yuryeva River–Sea of Okhotsk mixing zone. In different parts of the mixing zone, samples of solutions and bottom sediments were collected for subsequent geochemical analysis. To determine the thickness of potentially ore-bearing bottom sediments, a geophysical profile of electrical resistivity tomography was carried out, crossing the sea–river water mixing zone. River and sea waters, as well as bottom sediments to a depth of 31 m, were sampled geochemical analysis of solutions and solid particulate matter demonstrated specific elements (Zn, Pb, Cr, Co, Ni, V, Mn) deposited in the coastal zone and elements remaining in seawater and spreading further (Ca, K, Li, Mg, Na, B, Mo).