CTD Instrument and Water Sampler
Temperature and conductivity vs. depth profiles were carried out with a CTD, which stands for conductivity, temperature, and depth. Salinity can be computed. The instrument was lowered on a 11 mm diameter one-conductor cable up to 6000 m depth. AWI used a system from the manufacturer SEABIRD with the CTD type SBE 911plus*) and a water sampler type Carousel SBE 32 with 24 samplers, 12 litre each. After the profile the CTD/Carousel was carried into a special laboratory, thus samples can be taken while protected against the cold. The complete system consists of the underwater units, the deck command unit and a PC for data acquisition using SIEBIRDs software “SEASOFT” in its present version.
The CTD is equipped with double CT-senor pairs (SBE 4C*) and SBE 3plus)*). Both pairs are separately pumped using the SBE 5T*) pump. In addition the following external sensors or units were used: one oxygen sensor SBE 43*), a high precision thermometer SBE 35*), a transmissometer from WET Labs, type C-Star**), and an altimeter from Benthos, Mod. 2110-2.
Calibrations were made by SEABIRD before and after each cruise to apply drift corrections for the CT-Sensors. In addition water samples were taken from the Carousel and measured with the Guildline Autosal 8400B to confirm corrections resulting from the pre- and post-calibration. The temperature drift can be confirmed using the SBE 35. Using the comparison of the double sensor pairs provides the best way for data quality check. These procedures confirm the accuracy specified by the manufacturer as +- 0.001°K for temperature and +/-0.002 for salinity.