Water is heavy. For every ten meters of depth, pressure increases by roughly one atmosphere. At the average depth of the ocean the pressure is about 380 atmospheres; in the deepest trenches it exceeds 1,000 atmospheres.

This immense pressure shapes the biology and the technology of the deep sea. Proteins and cell membranes of deep-dwelling organisms are adapted to function under compression. Human-occupied and robotic vehicles must be engineered with thick pressure hulls or pressure-compensated systems. Instruments fail if seals or housings are inadequate.

Pressure also affects the solubility of gases, the equilibrium of chemical reactions, and the density of seawater. Oceanographers measure pressure with precision sensors and convert it to depth using known density profiles. The pressure gradient force, arising from horizontal differences in pressure, is a primary driver of ocean currents.

• Force exerted by the water column, increasing with depth
• Roughly 1 atmosphere per 10 meters
• Limits biology and engineering in the deep sea
• Measured to calculate depth and drive currents