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

14.03.2021 – And what happens during the rest of the year?

In the Bothnian Sea, Toralf and Volker will deploy a mooring. At the position they have chosen for it, the Baltic Sea is about 220 m deep. The heart of the mooring is a current meter, called an ADCP, which is connected to a heavy concrete block and thus anchored just above the seabed. From here, it can measure current speed and direction up to 30 m high in the water above it. It is equipped with probes that additionally measure salinity, temperature and oxygen, and numerous buoyancy bodies that keep the structure upright in the water. In total, the cable to which the devices and buoyancy bodies are attached is over 40 m long. Starting today, this combination of devices will operate fully automatically in continuous operation for about a year and store the measurement data obtained in the process - at a water depth of over 200m!

So it is already clear that the oceanographers have to come back to recover the mooring together with the anchor stone and the data. For this to succeed, a cable drum and a releaser are also attached to the steel cable. When the latter is activated, the devices detach from their anchor stone. Releaser and buoyancy bodies float up to the sea surface as the cable unwinds from the drum, pulling ADCP and its companion probes up with it.

In order to be able to retrieve the 170 kg anchor stone as well, it has been sunk with a 350 m long rope, at the end of which buoyancy bodies and a releaser are also attached. This ensures that nothing is left on the seabed. For me, this borders on a miracle, but Toralf assures me that it works. After all, several generations of oceanographers have tinkered with the mechanics, and it has already proven itself in countless projects.

And then it is lowered over the A-frame from the aft deck into the water - our little permanent measuring station. See you next year!

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