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The 51st cruise of the PV Akademik Sergey Vavilov (June 30–July 14, 2021) included the study of redox conditions in the Baltic Sea deeps. Water temperature in the upper quasi-uniform layer significantly exceeded average climatic values for July, especially in the Gulf of Finland (by 7–7.5°С) due to abnormally hot weather. A setup of cyanobacterial aggregates from the subsurface layer to the surface was observed, it occurred earlier than normal. In cooperation with the Immanuel Kant Baltic Federal University an integrated survey was carried out at the Kaliningrad carbon polygon and the IV International Summer School "Coastal Sea Zone: Research, Management and Perspectives" was held. [ABSTRACT FROM AUTHOR]

During the 56th cruise of the P/V Akademik Ioffe (August 2020) in the Baltic Sea, hypoxia was registered at a water depth of 80 m, hydrogen sulfide in the East Gotland Basin was detectable at 90 m above bottom, which is 25 m higher than in August 2019. In area of the "benthic desert" local habitats of species of bivalve mollusc Astarte borealis were found. Based on hydrophysical sounding data, a regional scheme of bottom currents induced by Major Baltic inflow events has been developed. High-resolution sub-bottom profiling and side-scan sonar in the East Gotland Basin allowed defining the thickness of marine sediments more precisely and revealing their asymmetry, as well as developing a digital terrain model. A detailed picture of the mosaic distribution of acoustic anomalies associated with the seeps of hydrocarbon gases to the bottom surface was obtained. New areas of distribution of iceberg plough marks, including buried ones, have been revealed. A previously unknown contourite drift was found in the northeastern part of the Slupsk Furrow. [ABSTRACT FROM AUTHOR]