The video showing sampling of the ocean floor with the multicorer (MUC) was taken at Station 12 (43 N, 177 E) during our cruise with the Sonne in the Pacific. It was one of the few stations at which the MUC team was able to collect samples during daylight hours.
…and what happens after the video?
Today Marion Pohlner, Julius Degenhardt and Bert Engelen, all from the Paleomicrobiology Group at the ICBM in Oldenburg, report on their work. Here on board they are the “MUC” team; their work focuses on microorganisms in sediments.
As soon as we have collected all of our samples from the sediment cores, we count the bacteria under the microscope. The picture below shows a sediment floc, which has a type of thread going through it. We don’t yet know exactly what the ‘thread’ is.
The small green dots are bacteria, which are stained with a green colored dye and are illuminated using ultraviolet light. Without the staining, we wouldn’t be able to distinguish the cells from the sediment. Since the bacteria are in different positions in the sample, they are at different focal lengths from the microscope objective. We took a series of photos and then combined them as a single picture. The program to do this was developed by Heribert Cyprionka (leader of the Paleomicrobiology Group at the ICBM), and is freely available at www.picolay.de.
How many bacteria live in sediments? At the sediment surface, on average we have counted 300 million cells per cubic centimeter. A cubic centimeter is about twice as much sediment as we collect in the cut-off plastic syring shown in the video. In a thimble full of sediment, therefore, there are as many bacteria as there are people in Germany! Twenty centimeters deeper in the sediment there are far fewer bacteria, but still approximately 3 million cells per cubic centimeter.
Why bacterial cell numbers decrease with depth in the sediments, and the reason why marine sediments have so many bacteria, is still not fully understood. In order to understand how bacteria live in sediments, we are measuring the enzyme activities of the bacteria. Enzymes cut up the organic matter in sediments, organic matter such as proteins and sugars; the bacteria can then take up the small pieces of organic matter, and use them to get energy and to build new cells.
All of these experiments are being done in the cold room, in order to have temperature conditions similar to the bottom of the ocean. In the deep ocean, and therefore in the sediments, temperatures are usually below 4 C. The cold room aboard Sonne is at 4 C; even when we were working with sediments collected near the equator, we needed to wear warm jackets!