Home run for the RV Maria S. Merian:
Research vessel sets off towards the Baltic Sea ice
for the "Deep Baltic" mission

13.03.2021 – Night owls on board: tireless CTD drivers

While we sample the ice during the day, we make our way perpendicular to the coast at night to record the properties of the Baltic Sea water here in the far north. We are interested in salinity, temperature and oxygen content and how these three properties change with increasing depth and ice cover. Salinity and temperature determine the weight of the water and thus the depth circulation. And since this is usually represented in filaments only a few kilometers in size, we need a close-meshed observation grid. On a total of 7 profiles we let the CTD probe into the water up to 15 times each to measure the properties of the water. Thomas, Ingo, Volker and Toralf took turns every two hours during the night. To support them, there was always one person from the other working groups, so that almost everyone had a CTD shift.

The result of this collaborative effort is an extensive data set that can be descriptively represented in diagrams - one for each profile and each measured value. On the diagram, created during the night of March 8-9, you can see that the cold surface water reaches great depths and begins to displace the warmer water at the bottom. This data is what the physicists were after. When all the profiles have been evaluated, they will reflect the development of deep water formation here in the ice-covered Bottenwiek. Thomas Neumann is not only pleased about the successful measurement campaigns. He will also feed his ecosystem model of the Baltic Sea with these data upon his return. "Our models are not yet accurate enough with regard to the energy and matter fluxes in the northern Baltic Sea. With these data, we are creating a big leap in quality. Only if the models represent the processes well can we use them to calculate scenarios. After all, we want to know how the northern Baltic Sea will behave when the ice cover recedes even further. That is the goal that we have now come a little closer to."

Text: Barbara Hentzsch (IOW)
Pictures: Ingo Schuffenhauer, Thomas Neumann (both IOW) | click pictures to enlarge