So, further to the wave question, how about pressure? How does the pressure in a fixed spot beneath a wave vary, and how does this change with depth?
The primary factor for pressure at any point in the water is depth. Deeper water means a higher pressure. So if you imagine your fixed point at a particular depth relative to a flat ocean, it will have some nominal pressure dependent on its depth. Waves passing induce a higher-than-nominal pressure at the fixed point as the crest passes overhead and a lower-than-nominal pressure as the trough passes. Basically, the waves cause a fluctuation in pressure around some nominal point. As you increase in depth, the fluctuation will have less and less effect because the nominal pressure is ever increasing.