CTD / Multisonde
During the first DISCOL cruise (SO61) a CTD-probe and the applied VGT-board unit (Video Graphic Terminal) were available as parts of the “Multisonde” manufactured by the German company “ME Meerestechnik – Elektronik GmbH”. Thereby, the probe was equipped with sensors to measure different physical and physico-chemical parameters, e.g. pressure (in dbar – which was later converted into water depth during pre-processing of the data), temperature (in °C), electric conductivity (in m s/cm), light transmission (%), dissolved oxygen (mg/l) and sound velocity (m/sec). The VGT-board unit provided an online calculation of the salinity in parts per thousand (ppt), taking into account the pressure, the temperature and the electric conductivity data.
In addition to the CTD-probe measurements, the multisonde was also equipped with a rosette water sampler to enable water sampling in different depths during only one profile. The water samples taken at eight locations during DISCOL 1 were mainly used to check the dissolved oxygen and the temperature sensors.
A total of seventeen vertical CTD-profiles were measured during the SO61 cruise, fifteen of which were located within the DISCOL area and two were taken during transit. However, the CTD-probe showed various problems during station work, which continued throughout the course of the SO64 cruise later in 1989 but still (after re-calibration and post-processing of the data) provided useful information on the general physico-chemical composition of the water column inside the DISCOL area.
During the DISCOL 3 cruise, only two hydrographic casts were conducted with the rosette water sampler and the CTD. One of these casts was used to calculate the sound velocity profile to aid the transponder navigation, whereas the other cast was just used as a technical test of the new multisonde. In both cases water samples were taken and were subsequently analyzed for oxygen concentrations at several depths inside the water column.The SO106 cruise featured a total of ten sampling stations involving hydrographic measurements in the water column (CTD and rosette water sampler). In addition to the parameters measured by the sensors of the CTD, the water samples were analyzed on board the ship for pH- and Eh-values, nutrient-type profiles (phosphate and silicate), dissolved heavy metals and dissolved oxygen (the sensor mounted on the CTD did not work properly during the SO106 cruise). Furthermore, a deep-sea pump system was deployed with the multisonde several times by fixing the pump on the frame of the rosette water sampler. The idea was to enrich the heavy metals in-situ by pumping seawater either into sample bags or over ion exchange columns to minimize the effects of contamination on board the ship before and during analysis.