Depth and pressure
At sea level the atmosphere exerts a pressure of 1 bar. This is the normal pressure that we feel. If you have ever been in an airplane, been up a mountain or dived in the ocean, you might have felt your ears pop. This is because of the air pressure changing.
Pressure underwater increases at 1 bar for every 10 meters (or 33 feet). This means that at 40 meters below the surface, where the deep reef team are working, the pressure is 5 bars, or five times greater than at sea level.
The deepest point in the ocean is the Challenger Deep, which is 10,994m (36,070 feet) deep. It is located in the Pacific Ocean, near the Mariana Islands group. The pressure here is about 1,100 bars. This is the equivalent of taking the Eiffel Tower, turning it upside down and putting it on your big toe. Only three people have been to the bottom of the ocean in specially designed submarines.