Deep Sea Jugs

[Inigo_Montoya]

Hi all! Here I am at the bottom of the Mariana’s Trench (shhh! my girl thinks I’m in Texas today!).

Because I am a highly inquisitive sort who frequently posts to the SDMB and devours the GQ section in particular, I know that water doesn’t compress appreciably and so is just as dense down here as it is near the suface. In the claws of my deep sea submersible I have a 1 gallon empty Miracle Whip jar (glass) which I am filling with Mariana’s Waters to give to my girl as a reminder of the depths I will go to on her account. Well, and I don’t have the bread for a diamond for her, but always have enough bread for…yeah, ok, stupid joke.

Anyways. My jar will have exactly 1 gallon of non-compressible Mariana’s Water in it as me submersible’s claw screws the lid back on. Oh look! There’s a little Paraliparis australis (let’s not worry about why it’s here in the trench, mmkay?) in the jar! Say hi to the little fishy!

Since I have other business down here in the trench I’ll send my jar of fish & water up to the surface on the express elevator, a separate vessel that goes straight to the surface with no decompression stops.

Something bad happens to my fish on the way up, but why? Water doesn’t compress, so there is still the same amount of water in my jar as before, so the fish couldn’t expand & pop. And if my jar fails, how? It never had any more than 1 gallon of water in it … did it?

[Kimstu]

@Inigo Montoya

In the claws of my deep sea submersible I have a 1 gallon empty Miracle Whip jar (glass)

You do? At 4 tons per square inch ambient pressure? Are you sure you don’t just have tiny shards of glass scattered over the ocean floor?

[Q.E.D]

Because water does compress, just not very much. And more to the point, glass isn’t perfectly rigid; it’s a little bit elastic as are all materials. So, the pressure inside the jar will push out and the glass jar itself will expand as the pressure outside drops. Thus, the pressure inside will always be roughly the same as that outside. As noted previously, if the pressure difference becomes greater than the jar can withstand, it will shatter.

Also, I thought this was going to be about submarine boobies. I’m disappointed.

[KneadToKnow]

There is not nearly as much discussion of mermaid mammaries in this thread as I had hoped for.

[Fubaya]

You still have the weight of all that water above you, it doesn’t matter if the water gets more compact or not. A ton of feathers weighs the same as a ton of rock. The pressure from the weight of the water acts on inert gases in the water. Nitrogen in the fish’s body is forced into suspension while at depth, but expands in shallow water. The fish died from the bends. When he exploded, shards of fish bones broke the glass, and a mermaid passing by was hit in the jugs by a bone and the blood attracted sharks and, well… it wasn’t very pretty from there…

[ElvisL1ves]

@Q.E.D

Thus, the pressure inside will always be roughly the same as that outside.

Only if the water inside and outside the jar can communicate. Otherwise, the tension on the jar wall will continue to increase until it fractures.

[Q.E.D]

@ElvisL1ves

Only if the water inside and outside the jar can communicate.

And they do. Glass is elastic enough to transfer pressure from the water outside to that inside, assuming there’s no airspace. Air is way too compressible, so the glass breaks long before the pressure inside rises much.

[Mangetout]

The elasticity of the container should maintain a slightly higher pressure inside, even if well within its elastic limit, although this effect may well be slight enough to fall within the bounds of Q.E.D.'s ‘roughly the same’

[slaphead]

@Inigo_Montoya

I know that water doesn’t compress appreciably and so is just as dense down here as it is near the suface.

Well that rather depends on your definition of ‘appreciable’ now doesn’t it?
From wiki

The low compressibility of water means that even in the deep oceans at 4000 m depth, where pressures are 4×10^7 Pa, there is only a 1.8% decrease in volume.

Given that you are at a depth of approx 11km, your water has actually compressed by a few percent relative to sea level and will unsquish quite noticeably on the way up.

[Tastes_of_Chocolate]

@Fubaya

Nitrogen in the fish’s body is forced into suspension while at depth, but expands in shallow water. The fish died from the bends.

Random question raised by the above answer:

Can fish get the bends? Since fish don’t breath air, do they actually build up nitrogen in their blood? What happens if you rapidly raise a fish from deep waters? I assume that there are issues having to do with the body being at less pressure then it was, but is there an equivalent to the bends?

[Autolycus]

I’m confused. So, the fish goes inside the glass jar, but the water pressure doesn’t only affect the glass jar, it also still affects the pressure of the water inside the jar?

What about when you take the jar inside the submersible?

[DrDeth]

@Tastes_of_Chocolate

What happens if you rapidly raise a fish from deep waters? I assume that there are issues having to do with the body being at less pressure then it was, but is there an equivalent to the bends?

Their swim bladder expands very rapidly, killing them.

[sqweels]

@Fubaya

The fish died from the bends. When he exploded, shards of fish bones broke the glass, and a mermaid passing by was hit in the jugs by a bone and the blood attracted sharks and, well… it wasn’t very pretty from there…

No, but the video would go viral in a heartbeat.

[DesertDog]

No cite, but I vaguely remember reading somewhere that sea-level would be about 200 feet higher if water was absolutely incompressible. I thought it odd as that just about what it would rise if all the polar ice melted.

[Chronos]

I’m confused. So, the fish goes inside the glass jar, but the water pressure doesn’t only affect the glass jar, it also still affects the pressure of the water inside the jar?

What about when you take the jar inside the submersible?

If you had an ideal unbreakable unstretchable jar, then the water inside would remain slightly denser than surface water, and therefore also remain at the incredible pressure needed to maintain that density. If you had a jar that was easily stretchable but not breakable, then if you brought the jar into a low-pressure environment (such as the surface, or the inside of your sub), the difference in pressure inside and outside the jar would cause it to stretch, until the water inside had expanded to its normal size, at which point the pressure would be balanced and it wouldn’t stretch any more. If you had a normal glass jar, then it probably wouldn’t be able to stretch that far before breaking.

[Autolycus]

@Chronos

If you had an ideal unbreakable unstretchable jar, then the water inside would remain slightly denser than surface water, and therefore also remain at the incredible pressure needed to maintain that density. If you had a jar that was easily stretchable but not breakable, then if you brought the jar into a low-pressure environment (such as the surface, or the inside of your sub), the difference in pressure inside and outside the jar would cause it to stretch, until the water inside had expanded to its normal size, at which point the pressure would be balanced and it wouldn’t stretch any more. If you had a normal glass jar, then it probably wouldn’t be able to stretch that far before breaking.

Ah, I get it now. Thanks

[Fubaya]

@Tastes_of_Chocolate

Random question raised by the above answer: Can fish get the bends?

Yes, even fish caught in rather shallow water. There is still more nitrogen in seawater than oxygen.