What is sigma pressure?

Sigma pressure refers to a concept in oceanography and meteorology that describes a specific way of measuring water density. It is defined as the pressure exerted by a column of water above a given depth, adjusted for the density of seawater, and is expressed in units of density (typically kilograms per cubic meter). Sigma pressure is useful for understanding stratification and circulation patterns in the ocean since it provides a clearer picture of how water layers interact based on their buoyancy. The most common forms include sigma-t (σt) and sigma-θ (σθ), which account for temperature and salinity variations.