An iceberg is a large piece of ice, which originates on land, floating in open water. See section 1.4.1.
An ice cap is a dome-shaped mass of ice that covers less than 50 000 km2 of land. See section 1.4.1.
An ice sheet is a dome-shaped mass of ice that covers more than 50 000 km2 of land. See sections 1.4.1, 1.4.2, 2.1.5.1, 4.1.4, 5.4.2 and 5.4.3.
An ice shelf is a thick platform of floating ice originating on land, which has flowed across the coastline onto the sea. The boundary between the grounded ice that rests on bedrock and the floating ice shelf is called the grounding line. See sections 1.4.1 and 1.4.2.
The instantaneous insolation is the energy received per unit time on 1 m2 of a horizontal plane at the top of the atmosphere (or equivalently on an horizontal plane at the Earth's surface if we neglect the influence of the atmosphere). It is measured in W/m2. The daily insolation is the total insolation received during one day (J/m2). See sections 2.1.3.3 and 5.4.2.
The internal energy of a system is the sum of the energy of all the particles in the system, measured by reference to the centre of mass of the system. For a perfect gas (a good approximation for the atmosphere), a solid, and an incompressible fluid (a good approximation for the ocean), it is function of the temperature alone. See section 2.1.5.
An interglacial is a relatively warm period between two glacial periods (ice ages). See sections 5.4.2 and 5.5.1.
The intertropical convergence zone (ITCZ) is a band close to the Equator where the trades wind of the two hemispheres meet, resulting in a convergence, rising air and heavy precipitation. See section 1.2.2.
An isopycnal is a surface of equal potential density in the ocean. The adjective isopycnal refers to changes or processes that take place along surfaces of equal potential density. Isopycnals are always very close to the horizontal but small deviations from the horizontal may have a large impact on ocean dynamics and on the representation of some processes (such as diffusion) in ocean models. See section 3.3.2.
Isotopes are atoms whose nuclei contain the same number of protons (and are therefore the same element) but a different number of neutrons. Isotopes have very similar chemical properties but different masses and different physical properties (some of which have an influence on chemical reactions). Isotopes can be divided into stable and unstable (radioactive) varieties. Radioactive isotopes decay and their abundance decreases with time, unless new isotopes are produced.
The isotopic composition of various archives, such as the water in ice cores, sediments in the ocean, three rings, etc, provides very valuable information on past temperatures, sea level changes, and exchanges between the various carbon reservoirs.
The isotopic composition is often estimated through a delta value (). For instance for 18O, a stable isotope of the oxygen, it is given by
where
is the ratio of 18O to the dominant isotope 16O in the sample being analysed, compared to the ratio in a standard reference sample. See sections 5.3.2, 5.3.3, 5.4.2 and 5.5.1.
Because of the different properties of the various isotopes, they can be partially separated during chemical reactions, phase changes or exchanges between different media, resulting in variations of the isotope ratio in different substances or phases. This isotopic fractionation can be due to isotope exchange reactions at equilibrium, or to kinetic processes which depend on differences in the reaction rates of the isotopes. See section 5.3.3.