CTD (conductivity, temperature and depth)

Deployment of the CTD

The sampling equipment consists mainly of a CTD/bottle Niskin/LADCP package to take full depth measurements of temperature, salinity, pressure, velocity and chemical tracers at each station. We also had underway measurements (surface salinity, temperature, chlorophyll, current + meteorological and bathymetry data).

The CTD package is lowered in the water down to the near bottom (typically 10–20 metres off of the bottom) measuring continuously temperature, pressure, conductivity (from which is derived salinity) and oxygen. On the way up to the surface, the Niskin bottles are closed at different depths to obtain a vertical profile of water samples. The depths at which the bottles are closed are chosen in order to sample the main water masses characterising the region of interest (the Weddell Sea in our case). Once on deck, the bottles are sampled by the different groups of chemists who will then either make their analysis on board whenever possible or they will store their samples to analyse them once back in the lab.

Different samples from the CTD

Temperature, salinity and pressure are three very important parameters for physical oceanographers as they determine the density structure of the ocean which in turns influences the circulation. By comparing the properties of water masses (temperature, salinity, content in various chemical tracers) with the same measurements made in the region during previous cruises, it is possible to characterise the changes that the water masses have undergone between the two cruises and hopefully to understand what drives the changes that we observe.