Seawater has a remarkably uniform composition that varies only in concentration. This means that the ocean is well mixed and thoroughly stirred around the entire earth. Cold water is generally more dense than warm water, thus sinking and displacing warmer water. Likewise, seawater with a larger amount of suspended sediments has a higher relative density than clear water, so it sinks and displaces clear water. Thus sediments, increased salinity, and decreased temperature will cause the greatest density of seawater.
Most waves move toward the shore at some angle.
As the wave crest nearest the shore starts to slow, the part still over deep water continues on at the same velocity. Thus, waves always appear to approach the shore head-on, arriving at the same time on all parts of the shore. As waves move from the deep ocean to the shore they pass over shallower and shallower water depths. After they reach water that is less than one-half the wavelength, friction progressively slows the bottom part of the wave. The wave front becomes steeper and steeper as the top overruns the bottom part of the wave.