Oceanological Research in the Northwest Pacific Ocean on the R/V Professor Kaganovsky and the R/V TINRO in June 2025

Abstract— The hydrological and hydrochemical structure of waters during summer 2025 and anomalies thereof are examined based on the results of two synchronous expeditions in the Northwest Pacific Ocean (NWPO) and the southwest Bering Sea (SWBS). Significant contrasting anomalies were identified: warming in the 0–500 m layer of the SWBS and a pronounced cooling of the surface in the southern NWPO, associated with the strengthening of the Oyashio Current. In addition to typical circulation elements, a powerful cyclonic gyre, significantly influencing the redistribution of parameters and causing upwelling of intermediate waters, was detected in the Pacific Ocean. Hydrochemical data revealed zones of high productivity (O₂ supersaturation up to 128% near Cape Olyutorsky) and the influence of mesoscale eddies on the distribution of nutrients. The results comprehensively characterize environmental conditions along the preanodromous Pacific salmon run in June 2025, which is important for fishery forecasting.