The zone where the breakers occur is called surf. Larger waves are produced by strong winds that blow for a longer time over a long fetch. A particle of water on the surface moves upward and forward with each wave crest, then backward and down on the following trough, tracing out a nearly circular path through this motion. The particle returns to its initial position, without any forward movement while tracing out the small circle. Note that the diameter of the circular path is equal to the wave height.
Water particles farther below the surface also trace out circular paths as a wave passes.
The diameters of these circular paths below the surface are progressively smaller with increasing depth. Below a depth equal to about half the wavelength there is no circular movement of the particles. The amount of dissolved salts in seawater is measured as salinity. Salinity is defined as the mass of salts dissolved in 1.0 kg, or 1,000 g of seawater. This is the same concentration as a 3.5 percent salt solution.