A CTD is an instrument used to determine how conductivity (C) and temperature (T) measurements in the ocean vary relative to depth (D) and is a primary tool for measuring physical properties of the ocean. Salinity is determined from electrical conductivity and is a measurement of the concentration of salt and other inorganic compounds in seawater. Salinity and temperature are two of the most basic measurements used by ocean scientists. The CTD temperature and salinity measurements are both used to determine seawater density, which is a primary driving force for major ocean currents.
Instrument specifications: CTDs were supplied by Sea-Bird; the models are SBE 16plusV2 and SBE 52MP.