Fascinating seafloor

Ahoy, dear SONNE friends!

Another day, another blog entry!
The following report was written by Marion Pohlner and Julius Degenhardt. The two scientists of the ICBM Oldenburg are from the research group Paleomicrobiology led by Prof. Dr. Heribert Cypionka.

Marion and Julius are using the MUC (multicorer) to take sediment samples from the seafloor


We are Julius Degenhardt and Marion Pohlner and today, we provide some insight into our research aboard R/V SONNE. We are scientists based at the ICBM Oldenburg and our work focuses on the seafloor.

In order to investigate the seafloor in more detail, we recovered samples from 5000 m water depth during this cruise. This was achieved this with a piece of kit called multicorer (MUC). On station, our MUC disappears for up to four hours in the deep blue sea. Once it reaches the seafloor, the coring tubes penetrate about 30 cm into the sediment. Two lids close the core tubes so that the sediment is well-trapped for the journey to the surface. In theory, this is very simple. Sometimes it is however challenging to recover sediments with the MUC depending on the properties of the seafloor which change from station to station. If the seafloor is too hard it can happen that the MUC comes back on deck with empty tubes…or huge ferromanganese nodules!

Once on deck, the sediments are recovered from the tubes and subsampled with sterile syringes from different depths. The samples are analyzed either directly on board or packed for shipping and analysis in our home lab at the ICBM. For instance, we identify the composition of the microbial community and the amount of bacteria within the sediment. Our bacteria cells are as small as 1-2 micrometers. Thanks to a particularly specific dye we are able to count such small bacteria cells. At the seafloor, we counted about 300 million cells per cubic centimeter. Twenty centimeters below the surface this number reduced to only three million.

Moreover, we analyze the enzymatic activity of bacteria. Enzymes breakup nutrients hosted by the sediment so that they become available for consumption by bacteria. As the temperature at the seafloor is around 4°C our analyses are carried out in the cold room.

But it’s not just the MUC recovering seafloor sediments. At some stations we also receive sample material from the ROV. Such sediments are mostly used to isolate yet unknown seafloor bacteria. Once the bacteria are isolated (i.e., only one species) we are able to investigate the nutrient consumption and the role of the bacterium at the seafloor in our home lab.

(Translation by Torben Struve)