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Sigma-t is a quantity used in oceanography to measure the density of seawater at a given temperature. [1] σ T is defined as ρ(S,T)-1000 kg m −3, where ρ(S,T) is the density of a sample of seawater at temperature T and salinity S, measured in kg m −3, at standard atmospheric pressure.
For the calculation of the thermodynamic properties of seawater and ice, TEOS-10 uses the specific Gibbs potential g(T,P)=G/m, G=F+pV, because the pressure is a more easily measurable property than density in a geophysical context.
The density of surface seawater ranges from about 1020 to 1029 kg/m 3, depending on the temperature and salinity. At a temperature of 25 °C, the salinity of 35 g/kg and 1 atm pressure, the density of seawater is 1023.6 kg/m 3. [7] [8] Deep in the ocean, under high pressure, seawater can reach a density of 1050 kg/m 3 or higher. The density of ...
These equations are formulated in the equation of state of seawater, also called the equation of seawater. This equation relates the thermodynamic properties of the ocean (density, temperature, salinity and pressure). These equations are based on empirical thermodynamic properties.
To calculate the weight of the displaced water, it is necessary to know its density. Seawater (1,025 kg/m 3) is more dense than fresh water (1,000 kg/m 3); [5] so a ship will ride higher in salt water than in fresh. The density of water also varies with temperature.
The density ratio of a column of seawater is a measure of the relative contributions of temperature and salinity in determining the density gradient. [1] At a density ratio of 1, temperature and salinity are said to be compensated : their density signatures cancel, leaving a density gradient of zero.
Temperature and salinity combine to determine the potential density of seawater; contours of constant potential density are often shown in T-S diagrams. Each contour is known as an isopycnal, or a region of constant density. These isopycnals appear curved because of the nonlinearity of the equation of state of seawater.
Direct density measurements are also used to estimate salinities, particularly in highly saline lakes. [4] Sometimes density at a specific temperature is used as a proxy for salinity. At other times an empirical salinity/density relationship developed for a particular body of water is used to estimate the salinity of samples from a measured ...