The brand-new CTD from ICBM – Germany’s largest CTD – is being used for the first time during this research cruise with the Sonne. In addition to valuable data, the CTD brings 24 large bottles of seawater from different depths on deck. Not ‘just’ water, but up to 480 liters with every cast.
Today’s report is from Kim Arndt, Thomas Badewien, and Holger Winkler, all from the ICBM group ‘Marine Sensor Systems’ in Wilhelmshaven. Here aboard the Sonne, they are the CTD team. They are particularly interested in the oceanography of the Pacific; they are also responsible for making sure that everyone on board gets enough water for his or her research project.
CTD stands for “Conductivity, Temperature, Depth”, three standard parameters that are continuously measured by sensor and reported real-time on deck when the CTD is deployed. The 24 water bottles (Niskin bottles) that are part of the CTD can be individually closed via remotely-operated switches; on board we can determine at which depths the CTD should collect water. Everyone is very interested when the CTD returns to the deck, full of valuable water. A detailed plan, worked out in advance, determines who gets water from which bottle; it is all worked out so that everyone gets what he or she needs for his or her work: sometimes a few milliliters, sometimes several hundred liters.
Most of the scientists aboard Sonne are interested in processes and
organisms that are found in the water column: the CTD is essential for these projects. At many stations, the CTD is deployed multiple times in order to obtain sufficient water. Even 480 liters are not
sufficient to satisfy the thirst of the scientific party. To date, we
have occupied 10 stations, and deployed the CTD more than 30 times. The depth of deployment is variable: a ‘deep’ station goes to the ocean floor, depths of 4000 to 6000 meters. At ‘shallow’ stations, we only collect water down to 1000 m depth.
The 30 CTD casts have provided more than 15,000 liters of water to the scientists: this is the equivalent of 1250 cases of cola, or almost
100 full bathtubs. This quantity is likely to double before we reach
the end of our cruise: there is still a lot of work to do.
After the CTD is back aboard the Sonne, we use the time until the next station to process the data prior to the next CTD deployment. In addition to temperature and salinity, we obtain data about oxygen
concentration, turbidity, density, and many other parameters. The CTD also provides data about chlorophyll fluorescence, so at each station we know precisely the depth at which most of the phytoplankton (marine plants) are living. To this point, the ‘deep chlorophyll maximum’ has been at depths between 60 and 120 meters. Other parameters show distinct differences in the water masses at different depths in the ocean. For example, the surface water is warm – still over 20 C – but the water temperature at a depth of 5200 m is less than 1 C. Humans without protection would not survive long at such cold temperatures, but many microorganisms thrive under these cold conditions.
See a short movie about the new CTD from the ICBM on board the research vessel Sonne: