A conductivity-temperature-depth profiler, or CTD, is an instrument lowered into the sea from a ship and used to measure the physical characteristics of the ocean and also to collect water samples.

Around the outside of the cylindrical frame are a series of bottles which can be triggered closed at various depths to capture a small volume of seawater. The collected water is then measured on the ship or ashore using very precise instruments, which can record carbon uptake or nutrients in the sample. In the centre of the frame is the electronic device used to measure conductivity, which is a measure of the saltiness of seawater, and temperature.

Just as temperature and humidity is important to us when describing weather on land, knowing the temperature and salinity of the ocean is vital for describing the ocean’s climate.

By looking at the changes in the temperature and saltiness of seawater, scientists can learn much about the densities of the different water masses that constantly move around the ocean.

For example, relatively warm fresher seawater may overlie a colder saltier layer, and both water masses may move in different directions to each other due to their variation in densities. By taking many water column measurements over a large geographic area and for a long time period, CTDs and their attached instruments can be used to detect the effect of climate change on the ocean.

Another use of the water samples is to detect the microscopic plankton, bacteria and viruses found within ocean water. By capturing those water samples at precise depths, the marine life found at those particular depths can be tested for their taxonomy, biochemistry and genetic characteristics.

The Gallery images and Movie below are examples of CTD dips and samples taken in Antarctica, the Great Barrier Reef and Coral Sea.

Gallery images

Movie