Oceanological Research in the Baltic Sea during the 56th Cruise of the Passenger Vessel Akademik Ioffe

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.