| Summary: | In 2018–2020 the research vessel (R/V) Professor Logachev (cruises 39 and 41) carried out geological and geochemical studies in the bottom waters of the Mid-Atlantic Ridge hydrothermal fields at 14°45’ N, 13°07’ N, and 13°09’ N. Two new hydrothermal fields were discovered—the Molodezhnoye and Koralovoye. Standard conductivity, temperature, and depth (CTD) sounding with a methane sensor was accompanied by video surveillance and sampling of rocks and water. The rocks were characterized by a zonal composition with opal and sulfides of copper and zinc. An increase in methane concentration values was accompanied by CTD anomalies in the bottom waters. The methane anomaly was formed within the hydrothermal plume of both high-temperature and low-temperature systems. Methane was almost absent in the plume of neutral buoyancy and was associated in all the studied manifestations with the ascending flow of hot waters over the hydrothermal vents. The hydrothermal plumes were characterized by increased Cu, Zn, and Fe concentrations at background Mn concentrations. Signs of low-temperature hydrothermal activity were also observed. Different sources and mechanisms are required to explain the elevated concentrations of base metals and methane in the hydrothermal plumes.
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