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

26.02.2021 – In the Arkona Basin

Preparations on deck

We are heading east. While we must be passing by the isle of Rügen laying somewhere in the South, the first preparations for the deployment of the gravity corer begin on deck: Steel tubes are taken out of the blue deck container and connected to each other and to the heavy weight head of the gravity corer in the so-called core support frame. Pipe after pipe moves into the rack - the plan is to take a 15-metre core in total.

First Station: Arkona Basin

Between the German and Danish coasts north of the island of Rügen lies the Arkona Basin - the first of the Baltic Sea basins behind the Darss Sill, which as a shoal inhibits the exchange of water between the North Sea and the Baltic Sea. Here we reach our first station with a water depth of about 50 m at around 4 p.m. Thomas Neumann and his colleague Ingo Schuffenhauer, who want to study the hydrodynamics in the Bothnian Sea, plan to “run” a first CTD here to check its performance and to get a first depth profile for comparison. As the CTD probe will be used a lot more on this voyage, today I am concentrating on describing the first deployment of the gravity corer, which was put to use directly after the CTD run.

Together with the core stacking frame, the device is hoisted over the railing in a horizontal position by means of a launching device and a crane. Then it is slowly brought into the vertical launching position, gets lowered into the water and is veered down to a point just above the seabed, where it is dropped abruptly. A set of weights at its upper end pushes the 15-metre corer tube into the seafloor, which is still relatively soft here. As the corer is pulled up, the marine deposits remain in the pipe, so that ideally we can bring a sequence of sediment layers in the full length of the pipe on board. Here, a plexiglas tube located within the steel pipe of the corer is pulled out with its sediement filling, which is then divided into 1-metre pieces and secured in place. Finally, the “harvest” of samples of a long day is stored on the large table in the ship’s hangar. 

Text and photos by Barbara Hentzsch (IOW) | click photos to enlarge