A variety of special instruments is needed for the marine biological research at sea. The department does not own all of these instruments, they are however frequently used on the "open sea" thanks to ongoing cooperations with partner institutes.
|
|
|
|
A conductivity probe is essential for the measurement of water temperature and salinity - and in combination: density. It calculates the salinity based on the electric conductivity of the surrounding water and measures the temperature at the same time. Conductivity probes exist as small handheld devices, and for use on large ships, the so-called CTD. The latter also measures the water depth with a pressure sensor (CTD = Conductivity, Temperature, Depth) and it is often equipped with water sampling bottles that can be closed at specific depths through an electrical signal fired down the cable from the ship control room.
Left: Handheld TS-sensor, right: CTD with sampling bottles in use at sea
The bottom water sampler is used to obtain samples of particle-loaded water from specific heights in the near-bed turbidity zone. The instrument is deployed on the seabed and it then automatically starts pumping water from the lowest centimeters above the ground into 4 large reservoirs.
Left + center: Deployment at sea, right: Close-up picture of the pumps and reservoirs
The department is in possession of a SAPS-pump (Stand Alone Pump System) for the in-situ water filtration at sea. This autonomous system can be pre-programmed to pump with up to 20 litres per minute through a 30cm-wide filter at a certain moment, i.e. at a given depth. This allows to obtain valuable information on suspended matter and its composition (POC, PON, lipids, etc.).
Picture of the pump system, lashed for the journey onboard a research ship
In coastal areas, this cable-camera can be used to gain a rapid insight into the water on the sea bed. It therefore allows to locate small-scale patterns of a sampling station prior to the use of larger sampling systems like e.g. BWS, GKG, MUC or the van Veen grab. In addition, the camera can also be used for a direct observation of the sea bed, provided the sea surface is not too rough.
Left + center: The camera system, right: Actual underwater picture from the Mecklenburg Bight
The USNEL (US Naval Electric Laboratory) box corer is used for large-surface, deep-ranging sediment samples. It consists of a box (20 or 50cm wide, 50cm deep) which is fixed at the lower end of a large plunger. It is lowered vertically until it impacts with the seabed. Weights force the box into the sediment and a spade swings underneath the sample to prevent loss when it is hauled. The device was developed about 30 years ago by Hessler and Jumars at the Scripps Institute of Oceanography in collaboration with the United States Naval Electronic Laboratory (USNEL) in San Diego, and is suited for a range of different sediment types.
Left: Box corer ready for deployment, with hoisted spade
Center: When hauled it back onboard, the spade is under the box
Right: Sideview of an unscrewed box with a sediment sample
A hydraulic dumper system avoids the bow wave effetcs by reducing the penetrating velocity of the cores into the sediment. This allows to sample even unconsolidated sediment layers and delicate organisms without damage. When lifted from the sediment surface, shutters swing underneath the cores to keep both sediment and the overlying water tightly sealed.
Left: MUC lowered into the water, right: Close-up picture of samples
The van Veen grab is used to extract sediment surface samples. It is held open by a securing mechanism, which releases as the grap penetrates into the sediment. The long lever arms tightly close the scoops during retrieval. This device is widely used for monitoring purposes and therefore has a standardised opening of 0.1 m2.
Van Veen grab in use on the university cutter GADUS
This fine-meshed net is used to sieve plankton samples from the water column into a collecting flask situated at its end. Some versions have a closing lid at the front opening which allows to collect samples from specific water layers. Even a quantitative determination of the plankton density is possible if the motion velocity of the net is known.
Plankton net
The large-scale collection of benthic organisms and bottom-living fish species is achieved with different trawl nets such as the dredge net or beam trawl.
Beam trawl hauled back onboard research ship FS ALKOR (Kiel)