Notes: A TSD and Bottle Station
TSD stood for “Temperature, Salinity and Depth”, later instruments were, and still are, referred to at CTD sensors.. “Conductivity, Temperature and Depth”, a more accurate description of what they measure. The TSD instrument was attached to a wire with a conducting cable core to allow the data to be monitored on the ship. A pinger unit might be attached below it, particularly if the sensor was being lowered close to the sea bed.
Bottles with reversing thermometers were attached to the wire at intervals. When the wire had been paid out to the full station depth a brass “messenger” was dropped down the cable. This triggered the top bottle, closing the end caps and allowing the thermometer holder to swivel which reversed the thermometers, breaking the mercury thread. It also released a further messenger so that all the bottles would be closed in a chain reaction.
Two of the three thermometers on each bottle were protected against the effect of pressure on the bulb but the third was not. The difference in readings allowed the depth of triggering to be determined. Thus the bottle string provided a course resolution temperature and salinity profile which could be used to check the accuracy of the continuous profile from the TSD, or to replace the TSD data if the latter instrument failed.
My job was clamping and removing the bottles from the wire, taking the bottles from and to the wet lab, reading the thermometers, and drawing the water samples into medicine bottles for later salinity analysis. To achieve the required accuracy a special procedure had to be strictly followed both when reading the thermometers and in rinsing out and filling the medicine bottles.