A conductivity-temperature-depth profiler, or CTD, is an instrument lowered into the sea from a ship and used to measure characteristics of the ocean and 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 machines 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 density. By taking many measurements over a long time, a CTD can be used to detect the effect of climate change on the ocean.
