Physical Oceanography Physical Oceanography Physical Oceanography 1573-160X 105671 EXPERIMENTAL AND FIELD RESEARCH EXPERIMENTAL AND FIELD RESEARCH EXPERIMENTAL AND FIELD RESEARCH Oxygen in the Bottom Layer of the Amur Bay Waters (Sea of Japan) During the Cold Season 2013–2014 Oxygen in the Bottom Layer of the Amur Bay Waters (Sea of Japan) During the Cold Season 2013–2014 https://orcid.org/0000-0003-2182-5477 Tishchenko Petr P. Tishchenko Petr P. eq15@poi.dvo.ru https://orcid.org/0000-0002-3500-2861 Tishchenko Pavel Ya Tishchenko Pavel Ya tpavel@poi.dvo.ru V. I. Il’ichev Pacific Oceanological Institute, Far Eastern Branch of Russian Academy of Sciences Россия V. I. Il’ichev Pacific Oceanological Institute, Far Eastern Branch of Russian Academy of Sciences Russian Federation V. I. Il’ichev Pacific Oceanological Institute, Far Eastern Branch of Russian Academy of Sciences Россия V. I. Il’ichev Pacific Oceanological Institute, Far Eastern Branch of Russian Academy of Sciences Russian Federation 15 05 2025 15 05 2025 32 4 479 491 06 12 2024 13 12 2025 https://ras.editorum.ru/en/nauka/article/105671/view

Purpose. This study aims to analyze oxygen concentration data from the bottom waters of Amur Bay during the cold season and to identify the causes of its decrease in late February to March, when the bay remains ice-covered. Methods and Results. Variations in bottom water characteristics during the cold season were investigated in the area of summer hypoxia at a depth of 22 m (1 m above the seafloor) using the Water Quality Monitor autonomous bottom station (Wet Labs). Temperature, salinity (measured by conductivity), dissolved oxygen (DO), and chlorophyll a (measured by fluorescence) were recorded every 4 hours. Monitoring data from the cold period of 2013–2014 were compared with the data previously collected at the same station and location in summer 2011. The basic patterns of changes in oxygen content and the periods of dominance of production and organic matter mineralization in the bottom waters of Amur Bay during the cold season were identified. Conclusions. During the winter season, upwelling of the Japan Sea waters delivers nutrients to the bottom waters of Amur Bay. Enhanced vertical mixing, driven by low water column stability, supplies the euphotic layer with nutrients, enabling photosynthesis throughout the bay’s water column. Over four months in winter, the Amur Bay waters become supersaturated with oxygen relative to atmospheric levels. The onset of the summer monsoon (late February to early March) initiates the formation of summer hypoxia in the bottom waters of Amur Bay.

Purpose. This study aims to analyze oxygen concentration data from the bottom waters of Amur Bay during the cold season and to identify the causes of its decrease in late February to March, when the bay remains ice-covered. Methods and Results. Variations in bottom water characteristics during the cold season were investigated in the area of summer hypoxia at a depth of 22 m (1 m above the seafloor) using the Water Quality Monitor autonomous bottom station (Wet Labs). Temperature, salinity (measured by conductivity), dissolved oxygen (DO), and chlorophyll a (measured by fluorescence) were recorded every 4 hours. Monitoring data from the cold period of 2013–2014 were compared with the data previously collected at the same station and location in summer 2011. The basic patterns of changes in oxygen content and the periods of dominance of production and organic matter mineralization in the bottom waters of Amur Bay during the cold season were identified. Conclusions. During the winter season, upwelling of the Japan Sea waters delivers nutrients to the bottom waters of Amur Bay. Enhanced vertical mixing, driven by low water column stability, supplies the euphotic layer with nutrients, enabling photosynthesis throughout the bay’s water column. Over four months in winter, the Amur Bay waters become supersaturated with oxygen relative to atmospheric levels. The onset of the summer monsoon (late February to early March) initiates the formation of summer hypoxia in the bottom waters of Amur Bay.

 Japan Sea Amur Bay dissolved oxygen hypoxia upwelling downwelling nutrients photosynthesis Japan Sea Amur Bay dissolved oxygen hypoxia upwelling downwelling nutrients photosynthesis The study was supported by the state programs of POI FEB RAS (registration numbers 121-21500052-9 and 121021700346-7). The authors express their gratitude to P.Yu. Semkin (POI FEB RAS) for the installation and retrieval of the bottom WQM station. The study was supported by the state programs of POI FEB RAS (registration numbers 121-21500052-9 and 121021700346-7). The authors express their gratitude to P.Yu. Semkin (POI FEB RAS) for the installation and retrieval of the bottom WQM station.

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