Spiciness (τ) is a term in oceanography that defines the salinity and potential temperature variation, often at constant density. Here, a temperature change offsets a salinity change; an increase in temperature decreases density whereas an increase in salinity increases density. Warmer and more saline water is spicier whereas cooler and less saline water is mintier. Mathematical description Quantifying the sea water density is necessary for describing thermohaline flow in the deep ocean. Changes in the two main parameters for this quantity, potential temperature Θ and salinity S, are multiplied with their thermal expansion or haline contraction coefficient equal to each other; and are both proportional to a change in density and are both terms of the linearized equation of state of the ocean (TEOS-10). This similarity is supposed to be relevant for understanding the consequences of sea water mixing. The density doesn't change over an isopycnal. However, by mixing a change in temperature and salinity can occur. Therefore spiciness is introduced as variable that is proportional to thermal expansion and haline contraction. Integration of this variable along an isopycnal leads to the following equation. Spiciness could be described as the isothermal gradient of the density that equals the isohaline gradient of the density. The isopycnal gradient of spiciness should equal to the isopycnal gradient of temperature and salinity by multiplication with the derivative in the other variable of the density. Another mathematical implication for the existence of a spiciness influence manifests itself in a -diagram, where the negative slope of the isopleths equals the ratio between the temperature- and salinity derivative of the spiciness. Applications A purpose for introducing spiciness is to decrease the amount of state variables needed; the density at constant depth is a function of potential temperature and salinity and of using both, spiciness can be used. If the goal is to only quantify the variation of water parcels along isopycnals, the variation in absolute salinity or temperature can be used instead because it gives the same information with the same amount of variables. Another purpose is to examine how the stability ratio varies vertically on a water column. The stability ratio is a number determining the involvement of temperature changes relative to the involvement salinity changes in a vertical profile, which yields relevant information about the stability of the water column: The vertical variation of this number is often shown in a spiciness-potential density diagram and/or