A mooring consists of up to several kilometres of Kevlar rope, on which various instruments are mounted at certain intervals. Buoyant floats attached to the rope keep the mooring almost vertical in the water column. They also force the mooring back to the surface upon release of the bottom weight. Usually, these floats are evacuated glass spheres of 17’’ diameter, which are protected by plastic covers. The floats are pressure resistant to 6000 m water depth and are amazingly robust. Each single float gives a buoyancy of about 25 kg. Releasers are situated right above the bottom weight. These instruments are mechanical actuators which will separate the mooring line from the bottom weight upon an acoustical signal sent by the mother ship.
Moorings may be equipped with a variety of different oceanographic measuring and sampling devices, e.g. Aanderaa current meters and sediment traps supplied by the German company K.U.M.. The acoustic current meters we use determine the current speed and direction in pre-selected time intervals by evaluating the Doppler effect of the surrounding waters at the respective depth. The sediment traps catch particles of biotic and abiotic origin that sink through the water column. As the particles are preserved in vials that can be exchanged by a revolver system at predetermined time intervals, the seasonal variability in particle flux can be determined with a temporal resolution of a few days to several weeks.
At the moment, we are working on a special mooring with an underwater winch as a top buoy at about 150-m water depth carrying a sensor platform. This platform will profile surface waters once a day to register gradients in temperature, salinity, oxygen, carbon dioxide, and chlorophyll fluorescence at high resolution. At a later stage, this profiler will be equipped with a satellite communication system to allow receiving "near real time" data from the study area. To impede damage of the sensor platform during periods of sea-ice coverage or in stormy weather conditions, the platform will carry a safety system, which will keep the profiler temporarily at depth.
A sketch showing the typical configuration of our moorings could be found here
Contact: N. Lochthofen, E.-M. Nöthig, I. Salter