Russian Journal of Earth Sciences Russian Journal of Earth Sciences Russian Journal of Earth Sciences 1681-1208 75314 10.2205/2024ES000938 rpylfx ОРИГИНАЛЬНЫЕ СТАТЬИ ORIGINAL ARTICLES ОРИГИНАЛЬНЫЕ СТАТЬИ Methane in the Water Column of the Gdansk Deep (Baltic Sea): Seasonal and Vertical Variability Methane in the Water Column of the Gdansk Deep (Baltic Sea): Seasonal and Vertical Variability https://orcid.org/0000-0002-1085-4179 Ульянова Марина Олеговна Ulyanova Marina Olegovna marioches@mail.ru Корнеева Анна О. Korneeva Anna O. Институт океанологии им. П.П. Ширшова РАН P.P.Shirshov Institute of Oceanology of the Russian Academy of Science Балтийский федеральный университет им. Иммануила Канта Immanuel Kant Baltic Federal University 23 10 2024 23 10 2024 24 5 1 18 16 02 2024 16 10 2024 https://rjes.ru/en/nauka/article/75314/view

The study of the vertical distribution of methane dissolved in water and related parameters (water temperature and salinity, dissolved oxygen concentration) was carried out in 2021–2023 at the offshore carbon supersite Rosyanka in the Gdansk Deep of the Baltic Sea. Measurements with such frequency (a total of 16 surveys) were carried out in the region for the first time. Methane concentrations varied over a fairly wide range (0.000–1.122 μmol/L), and increased with depth, which is a typical distribution for the Baltic Sea and is associated with the vertical stratification of the water column. Single maximum values were characteristic of the layer extending from the bottom to the upper boundary of the halocline, which indicates the flow of methane from bottom sediments into the water column. In the near-surface layer (5–15 m), a weakly pronounced peak in methane concentrations was observed, which is a manifestation of the “oceanic methane paradox”. No pronounced seasonality was detected in the vertical distribution of dissolved methane; the correlation between temperature, salinity, oxygen, and methane content turned out to be low.

The study of the vertical distribution of methane dissolved in water and related parameters (water temperature and salinity, dissolved oxygen concentration) was carried out in 2021–2023 at the offshore carbon supersite Rosyanka in the Gdansk Deep of the Baltic Sea. Measurements with such frequency (a total of 16 surveys) were carried out in the region for the first time. Methane concentrations varied over a fairly wide range (0.000–1.122 μmol/L), and increased with depth, which is a typical distribution for the Baltic Sea and is associated with the vertical stratification of the water column. Single maximum values were characteristic of the layer extending from the bottom to the upper boundary of the halocline, which indicates the flow of methane from bottom sediments into the water column. In the near-surface layer (5–15 m), a weakly pronounced peak in methane concentrations was observed, which is a manifestation of the “oceanic methane paradox”. No pronounced seasonality was detected in the vertical distribution of dissolved methane; the correlation between temperature, salinity, oxygen, and methane content turned out to be low.

 dissolved methane carbon supersite thermohaline conditions hypoxia dissolved methane carbon supersite thermohaline conditions hypoxia Hydrophysical conditions and oxygen content were analyzed with a support of the state assignment of IO RAS (Theme No. FMWE-2024-0025). The methane research was supported by the state task of the Ministry of Education and Science of the Russian Federation, topic No. FZWM-2024-0015 (IKBFU). The authors thank the staff of the IO RAS for providing primary hydrophysical data and determination of dissolved oxygen: V. Krechik, E. Bubnova, A. Muratova. Hydrophysical conditions and oxygen content were analyzed with a support of the state assignment of IO RAS (Theme No. FMWE-2024-0025). The methane research was supported by the state task of the Ministry of Education and Science of the Russian Federation, topic No. FZWM-2024-0015 (IKBFU). The authors thank the staff of the IO RAS for providing primary hydrophysical data and determination of dissolved oxygen: V. Krechik, E. Bubnova, A. Muratova.

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