INTRODUCTION

When we talk about pressure in the ocean, we are referring to hydrostatic pressure, which is a result of the weight of the water column pressing down on an object due to gravity. The deeper you go, the more water that is above you, and the greater the weight (and thus pressure) of that water. At the surface we experience one atmosphere of pressure (1 atm = 101.3 kPa) due to the weight of the atmosphere above us. As you descend into the ocean, pressure increases linearly with depth; there is an increase in pressure of 1 atm for every 10 m increase in depth. So at 1000 m depth the pressure would be 101 atm (100 atm of pressure due to the 1000 m depth, plus the 1 atm that is present at the surface). This leads to very high pressure in the deeper parts of the ocean; if you consider that the average depth of the ocean is about 3800 m, the pressure at that depth would be 381 times greater than the pressure at the surface. The density of seawater is increased by increasing pressure. Density changes about 2% because of the pressure difference between the surface and the deep seafloor. The effect of pressure on density usually can be ignored because most applications require density comparisons between water masses at the same depth.