How do temperature and pressure change and descend from the surface to the ocean floor?

Answer 1

Pressre increases as you move from the surface to the ocean floor. The pressure is a result of the weight of the water above. The deeper you go, the more water you will have above you and the greater the weight and thus pressure.

In general temperatures decrease as you move from the surface to the ocean floor. The simplest reasons for this are:

1. the energy of the sun does not penetrate deep into the ocean so the lower layers cannot be warmed by it
2. colder water is more dense and sinks while warmer water rises

This is only a general rule however. Near thermal vents, the temperatures can be above the boiling point of water - even at the high pressures found at the bottom of the ocean.

The decrease in temperature is not a smooth one. Much of the ocean has a layered temperature structure. The sun-warmed surface water mixes with cooler, deeper waters as winds, breaking waves and turbulent currents stir the water. One result of this mixing is a surface layer having nearly uniform temperature, or isothermal, conditions. The temperature of seawater immediately below the mixed layer changes rapidly with depth. This layer of rapid temperature change extends down to about 1,000 m and is called the main thermocline. The main thermocline separates the warmer mixed layer above from the cooler deep layer below. In the deep layer, the water is almost isothermal, with only a gradual decrease in temperature to the ocean floor. The deep layer starts at a depth of around 1,000 m and extends to the ocean floor.