Deep water formation is the process through which the water masses acquire their characteristics (in particular, their temperature and salinity) at the surface before sinking to great depths. In the deep ocean, the temperature and salinity change very slowly. As a consequence, the properties of the waters found at great depths in the ocean can be traced over very large distances to their origins (their ‘formation’) at the surface. See section 1.3.3.2 and see also water mass formation and thermohaline circulation.
The diapycnal direction lies at right angles to the local isopycnal surface. Consequently, the angle between the diapycnal direction and the vertical is very small. See section 3.3.2.
Dissolution is the process by which a solid or liquid forms a homogeneous mixture with a solvent (in climatology the solvent is generally water). During this process the crystal lattice of the solid is broken down into individual ions, atoms or molecules.
Dissolved inorganic carbon (DIC) is the sum of the concentration of the three forms of inorganic carbon present in the ocean (i.e. carbonic acid, H2CO3, bicarbonate, HCO3- and carbonate ions, CO32-). See section 2.3.2.1 and 4.3.1.
A downwelling is a downward movement of water in the ocean. See also upwelling.
Dry air is air without its water vapour. Air (or moist air) is composed of dry air plus water vapour. See sections 1.2.1.