Hydrostatic pressure increases with depth in the ocean. At sea level, the pressure is 1 bar or 14.7 pounds per square inch (PSI). With depth, the pressure increases by about 1 bar per 10 meters.
Human bodies are not built to withstand pressure at depth without special gear or submersibles, however, marine animals are built for pressure. For example, whales are specially adapted with flexible bodies and rib cages that allow them to swim at depth without injury. According to NOAA, the pressure at the deepest part of the ocean is equivalent to a person holding 50 jumbo jets or an elephant supported by a postage stamp.
While on research vessels, it is common for scientists to bring along decorated styrofoam cups and styrofoam wig heads to send down in the ocean. This is because styrofoam shrinks with depth and retains the same shape. Styrofoam is made of polystyrene foam and is full of air pockets. When styrofoam is sent down at depth in the ocean, the pressure pushes out the air and what is left is a great example of what pressure can do with depth.
Several team members brought decorated styrofoam cups and heads to shrink at depth. On the Healy, the styrofoam cups and heads were sent down in a bag on the CTD or rosette sampling unit to a depth of 2712 meters (1.685 miles). At the time, the Healy was located at 83° 18’ 8” N Latitude and 162° 08’ 6” W Longitude. The pressure at 2712 meters deep is approximately 3987 PSI or 271 bars!