What is a CTD cast?

A CTD cast is primarily referred to as a method for measuring the temperature, salinity, and depth of seawater. The acronym CTD stands for Conductivity, Temperature, and Depth. This technique involves deploying a CTD instrument, often attached to a frame with water sampling bottles, into the ocean. As the device is lowered through the water column, it collects data at various depths, allowing scientists to analyze the physical properties of seawater.

Understanding these parameters is crucial for various oceanographic studies, including the analysis of water masses, buoyancy, and the stratification of the ocean. Temperature and salinity are particularly important as they influence the density of seawater, which in turn affects ocean circulation patterns and the overall health of marine ecosystems. This data can be used to inform climate models, monitor environmental changes, and study marine life habitats.

The other options relate to different aspects of oceanography, but do not accurately define what a CTD cast is. For instance, sampling phytoplankton would use a different technique, oceanographic models do not pertain specifically to direct measurements obtained from the CTD deployment, and air pressure measurements are not relevant to the underwater data collection carried out by a CTD.