Seawater density

Seawater density is the mass of seawater per unit volume. It varies chiefly with temperature, salinity, and pressure, shaping ocean circulation and vertical layering.

Temperature: Temperature measures the thermal state of matter and influences its physical properties. Warming seawater generally expands it, lowering density when salinity and pressure stay constant.
Thermohaline circulation: Thermohaline circulation is large-scale ocean circulation driven by seawater density differences associated with heat and salt. Density contrasts help sink and transport water masses through the global ocean.
Density: Density is mass per unit volume of a substance. Seawater density is a specific application of this general physical quantity.
Potential density: Potential density is the density a seawater parcel would have at a chosen reference pressure after adiabatic adjustment. It removes pressure’s direct compression effect for comparisons between depths.
Salinity: Salinity is the concentration of dissolved salts in water. More dissolved salt generally increases seawater’s mass per unit volume.
Ocean stratification: Ocean stratification is the layering of seawater with different densities, limiting vertical mixing. Density differences determine the strength and persistence of ocean layers.
Potential temperature: Potential temperature is the temperature a fluid parcel would have if moved adiabatically to a reference pressure. It separates temperature changes caused by compression from other oceanographic temperature differences.
Neutral density: Neutral density is a seawater coordinate designed to track surfaces along which water parcels move with little buoyancy change. It offers a way to describe ocean layers that does not simply use in-situ density.
Hydrostatic pressure: Hydrostatic pressure is pressure exerted by a fluid at rest under gravity. Increasing pressure compresses seawater, raising its density at depth.
Deep water formation: Deep water formation is the process by which surface water becomes dense enough to sink into the ocean interior. Cooling and salinity increases can make surface seawater sink.

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