Ocean stratification

Ocean stratification is the layering of seawater by density, shaped chiefly by temperature and salinity differences. It limits vertical exchange between water layers.

Seawater density: The mass per unit volume of seawater, determined chiefly by temperature, salinity, and pressure. Density differences set the stability and strength of ocean layers.
Ocean mixed layer: The near-surface ocean layer kept relatively uniform by wind, waves, and convection. Its depth marks the upper boundary of the more strongly layered water below.
Seasonal thermocline: A temperature-gradient layer that forms in the upper ocean during seasonal surface warming. It strengthens summer stratification and often weakens when winter cooling deepens mixing.
Thermohaline circulation: Large-scale ocean circulation influenced by differences in temperature and salinity. Stratification affects where dense waters form and how readily they sink and circulate.
Double-diffusive convection: Fluid motion driven by unequal diffusion rates of heat and dissolved substances, such as salt. It can generate fine-scale mixing within otherwise stable temperature-and-salinity layers.
Thermocline: A layer in which water temperature changes rapidly with depth. In the open ocean, this temperature gradient often creates a strong density barrier.
Ocean ventilation: The transfer of surface waters and dissolved gases into the ocean interior. Strong stratification can restrict the renewal of deep waters from the atmosphere.
Permanent thermocline: A persistent temperature-gradient layer beneath the seasonally variable upper ocean. It separates warm surface waters from colder interior waters in much of the ocean.
Atlantic meridional overturning circulation: A system of northward surface flow and southward deep flow in the Atlantic Ocean. Freshening and stronger upper-ocean layering may affect deep-water formation in the North Atlantic.
Convective overturn: Vertical fluid motion that occurs when denser fluid overlies lighter fluid. Unlike stable stratification, this instability drives rapid vertical exchange.

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