Bottom-Lander
The conventional approach in deep-sea studies is to collect samples at the seafloor, to recover them, and to make observations and analyses on board the research vessel or later at the home lab. However, because of artefacts induced when samples are subjected to changes in hydrostatic pressure and (often) temperature during transfer to the surface, accurate data from the deep sea are difficult, if not impossible to obtain. It is therefore preferable to carry out observations, experiments and measurements directly at the seafloor. Such studies can be conducted using free-falling lander systems ("benthic landers").
A benthic lander is an unmanned vehicle that falls to the seafloor unattached to any cable, and then operates autonomously at the bottom. At the end of the deployment, ballast weights are released pre-programmed or on acoustic demand. The lander floats back to the surface by virtue of its positive buoyancy.
The project group runs different systems of basically the same design (GEOMAR-type). These systems, however, were used for different purposes and are therefore equipped with different scientific modules, e.g. with respiration chambers (see below) and a microprofiler to assess carbon remineralisation processes through the benthic community, or with a sonar system and still cameras for the detection of motile epibenthic organisms and their reaction to large food-falls (see below). Other systems, usually moored for a year, are equipped with currentmeters and sediment traps to quantify the flux of particulate organic matter to the seafloor.
Bottom lander at the deep seafloor:
In situ respiration chambers
Remineralisation processes at the seafloor can be quantified with respiration chambers, which isolate a limited area of the sediments (including benthic organisms) together with the overlying water. A time-interval subsampling of the overlying water and subsequent chemical analyses allow assessing the oxygen uptake by the sediment-inhabiting community during incubation. To assure mixing and to maintain hydrodynamic conditions as natural as possible, the chambers are equipped with water mixing mechanisms (magnetic stirring bars).
Contact: B. Sablotny, T. Soltwedel
Sonar system for the detection of motile epibenthic organisms
The project group runs a digital scanning sonar manufactured by Kongsberg Simrad Mesotech Ltd., which enables to detect moving particles (also organisms) in 360° around the sonar head. The control system for this sonar has been designed at AWI to allow autonomous operation as part of a freefalling lander system.
The main objective to use such a sonar system was to detect movements of scavengers (e.g. amphipods, fishes) attracted by artificial "foodfalls" over long distances. Because of the physical and technical properties of the sonar head, the instrument allows the detection of objects larger than 2 cm at a minimum distance of less than 10 m and a maximum distance of about 100 m. The visualisation of the measured data with the system reminds of radar images.
Sonar recording:
Contact: M. Klages
Literature:
Premke, K., Muyakshin, S., Klages, M. & J. Wegner (2003). Evidence for long range chemoreceptive tracking of food odour in deep sea scavengers by scanning sonar data. Journal of Experimental Marine Biology and Ecology 285-286: 283-294.
Premke, K., Klages, M. & W.E. Arntz (2006). Aggregations of Arctic deep-sea scavengers at large food falls: temporal distribution, consumption rates and population structure. Marine Ecology Progress Series 325: 121-135.