Abstract
The EMB217 cruise was dedicated to the DFG-Funded project ROBOTRACE (The role of bottom boundary layer turbulence for the exchange of tracer) and was the third in the project. The purpose was to sample the ROBOTRACE stations during a calm summer season. This allows to understand the seasonality of the oxygen transport in the central Baltic Sea. The sampled stations and main transect were on the eastern part of the Gotland Basin (TS1, Fig. 3.1). For the background condition during the cruise, two moorings chains, including ADCP, T, S and oxygen sensors, were deployed along the transect. Short term deployments of oxygen microprofilers, oxygen eddy-covariance and chamber landers were performed along the transect. The transect was sampled several times with a shear microstructure probe (MSS-90L) including a fast response oxygen optode and accompanied by nutrient samples taken with watersamplers mounted on a standard CTD rosette. Besides these main tasks, maintenance of the IOW longterm mooring NE and GODESS were performed and a lagrangian drifter (Jetsam, Univ. Florida) was tested for its use in the Baltic Sea.
During this short cruise, we explored the potential of acoustic echo sounding techniques (wideband single-beam and multibeam systems) for the quantitative investigation of turbulence and other small-scale processes in the water column. These activities were embedded in the research project „Four dimensional Research applying Modeling and Observations for the Sea and Atmosphere“ (FORMOSA), funded by the German Leibniz-Association (WGL) in the framework of the national funding line “Cooperative Excellence”. The cruise took place in May 2021 in the Kattegat region and the western Baltic Sea (Arkona Basin). Our activities focused on the mixing of salty North Sea waters and brackish outflow waters from the Baltic Sea in the Kattegat region with the help of turbulence microstructure and acoustic observations. Measurements were conducted by scientists from IOW in collaboration with project partners from Stockholm University (Sweden) and an additional engineering group from Rostock University (Germany).