Pressure under the sea

[Lorence]

Hi Guys....The deeper one goes in the sea the greater the pressure gets to the extent that a diver can't withstand and even submarines can be damaged if they go too deep.....In that case how on earth do fish survive without being squashed at those pressures.....Thanks for any info.

[Lakitu]

This para is taken from wiki, which explains it well:

Due to the extreme pressure of the sub-photic zones, these animals have had to adapt using the process of natural selection in order to survive. The pressure increases by about one atmosphere every ten meters, creating tremendous pressure when going down thousands of meters deep. In order to cope with the pressure, many fish are rather small, usually not exceeding 25 cm in length. Also, scientists have discovered that the deeper these creatures live, the more gelatinous its flesh and the more minimal its skeletal structure. These creatures have also eliminated all excess cavities that would collapse under the pressure, such as swim bladders.

http://en.wikipedia.org/wiki/Deep_sea_creature #Pressure

[jake-the-peg]

I think you're misunderstanding the problem.

The inside of a submarine is normally at the same pressure as the surface.

So every 10 meters increases the pressure by 1 atmosphere which is why they have to be so strong.

If you increased the pressure inside the sub to the same as outside then they would not need to be so strong, the pressure inside would balance the pressure outside.

A diver at 30 meters would have his lungs crushed if he had air at surface pressure in them.

As you go deeper an aqualung supplies air at higher and higher pressures so the air in your lungs is at the same pressure as the water outside.

The reason that divers are limited by depth is not so much the pressure on the body but, put simply, because the oxygen we breath becomes toxic to us at a certain pressure.

The real question ( and I'm not sure I know the answer ) is not why the fish are not squashed flat - that's because their bodies are at the same pressure as the surrounding water and they have no cavities like lungs- but rather how they survive biochemically without being poisoned

[Lorence]

Thanks for that guys......Now I know.....cheers

[hambletta]

in simple terms, the reason fish have adapted to these pressures is that they do not have lungs which are collapsable. their main body parts are mostly solids and fluids, thereby equalling and so nihilating the outside pressure.

think of it this way, if you were at the bottom of the marianas trench and filled your lungs with water then your internal pressure would be the same as the outside pressure, therefore neutralising extreme pressure.

[wildwood]

And likewise, deepsea fish (abyssal fish) brought up to the surface too quickly suffer from decompression symptoms and usually die before they are lifted out of the water, it is like opening a bottle of fizzy drink.

[beso]

More fascinating stuff. Aside from the narcotic effects of too much oxygen or nitrogen there is another problem with increasing pressure.

As the diver goes deeper the density and viscosity of the gas supplied to their lungs gets higher. The increased viscosity makes it harder to breathe.

Helium is substituted as part of the mix. It has small molecules so the viscosity is lower. Eventually it too becomes too thick to breathe.

The ultimate substitute is to breathe a liquid. A special low viscosity liquid that can transport oxygen. It is also hard to breathe but it doesn't increase in viscosity with further depth because it doesn't compress.

Only the really brave or foolish get into this technology.

People who free dive to great depths actually empty their lungs before diving. Whales also do this.

[heathfield]

Yet beaked whales have been observed to dive to depths of nearly 1900 metres. Amazing! :-0