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I am developing an ocean world for a story involving marine mammals, and the biggest issue I cannot settle on is whether to have deep or shallow civilisations.

The main concern is that their architecture will include heavy use (perhaps even exclusive use before they develop air and water tight seals) of moonpools and airbubbles, for the purposes of this question assume that this is a non-negotiable factor when formulating an answer.

How would airbubbles/moonpools (where the top portion of a room is air) be achieved deep in the water, are they even possible? I am asking in regards to scientific possibility and practicality, not how would the species literally find the air and transport it, for which I already have some ideas. Assume the species has access to plants that recycle the air aswell.

The planet has earth-like astronomical and meteorological conditions but is not earth and not close to fully formed in my mind yet, so feel free to adjust the planet's atmospheric composition or the composition of the seawater whilst keeping it fundamentally earth-like if that provides avenues to a solution.

EDIT: I imagine that the species would initially build primitive open-entrance shelters in shallows where quick access to the surface is possible. As their ability to farm coral (including selective cultivation of watertight species for instance) and manipulate it as a building resource increases I envisage that they would have less reliance on the shallows and move deeper to exploit resources in the depths, just as humans did in regards to coastal civilisation spreading inland.

I am fairly set on their buildings being for the most part coral domes entered from the base, like igloos, and featuring moonpools and ledges to provide living space and a dry area for whatever purposes that may serve. The entrance into the dome would be swam through and the surface of the moonpool above the entrance.

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  • $\begingroup$ How can these structures predate airtight construction while containing air pockets underwater? Anything short of domes carved from solid stone will leak the captured air. Am I misunderstanding the question? $\endgroup$ – rek Jan 10 at 22:50
  • $\begingroup$ My apologies I should have clarified that in my OP. I will make an appropriate edit. $\endgroup$ – FrankRebin Jan 10 at 22:56
  • $\begingroup$ @rek How are leaks enough of a problem to be prohibitive? Yes, in the early stages of this species's development from pre-sapient to technologically-advanced culture, there will likely be a lot of leakage going on, and even in the later, high-tech stages, they're gonna be losing some air all the time to dissolution in the water, if the air and the water have any contact at all, but all that means is that the leakage rate puts a lower bound on how fast they have to be importing replacement air from the surface. $\endgroup$ – Matthew Najmon Jan 10 at 23:31
  • $\begingroup$ What is the problem this question seeks an answer to? You've already established that they can get the air from an abundant, naturally-occurring source, and that they have a means of harvesting it from that source and delivering it to the moonpools. Are you looking for answers addressing how they go about creating suitable architecture with which to trap the air, without such tools as fire that would be especially difficult for marine dwellers, or answers more addressing issues such as how high the pressure can get and still be able to keep significant amounts of the air undissolved? $\endgroup$ – Matthew Najmon Jan 10 at 23:35
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    $\begingroup$ @Matthew Najmon I am trying to find out, from a biology and physics perspective, does a moonpool work the same way at depth under high pressure as it does in shallows? Would extra tech be required to force high pressures of air into the domes, would a typical air breather beable to breath that air without oxygen toxicity, does the pressure down there simply prohibit the strucute entirely? So overall, from a scientific perspective is it possible or would my species have to be severely modified or is it simply impossible? This is all assuming they have the material ability to achieve it. $\endgroup$ – FrankRebin Jan 11 at 0:06
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Just build an air-tight room that's open at the bottom and put air in it. That's all you need to do.

A pool full of air surrounded by water will behave in pretty much the same way as a pool full of water surrounded by air. The biggest difference is that air "falls" up in water instead of down, which is why your pool has to be open at the bottom, not the top.

There's no special technology needed to get the air down there. You can literally just go up to the surface, fill a bucket with air, take it down to the pool, and dump it out. Pressure is not a problem; even a mile underwater, where the pressure is about 150 atmospheres, an ordinary bucket would hold the water just fine.

The problems that a human being would encounter trying to breathe the air in that pool are the same as the problems that scuba divers already encounter at great depths. Wikipedia says that ordinary air "is considered to have a safe depth limit of about 40 metres (130 feet) for most divers," so if your pool is no lower down than that, then humans and human-like creatures should be able to breathe.

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  • $\begingroup$ As I stated in my question I am interested in deep water, which relative to an earth-like ocean planet would be much more than 40m, more like 1000m. I am glad to hear that extra technology wouldn't be required to create the air bubble at such high pressures, but I am still unsure as to whether it would be biologically possible for a naturally epipelagic marine mammal as specified. To clarify I wouldn't consider that to be human-like. Thankyou for your time and consideration in answering! :) $\endgroup$ – FrankRebin Jan 11 at 0:53
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After doing some considerable reading on my own it appears that airbubbles at such depth are not possible for use as habitats for my current model of fictional species.

This is because although marine mammals have developed an adaptation to counter decompression sickness, the fact they do not breathe at depth means they have no need to develop resistance to oxygen toxicity.

I may write a follow-up question on what adaptation would best provide the ability to resist oxygen toxicity at depth, and what ecological conditions my ocean world would need to facilitate selection for such an adaptation in a diving marine mammal.

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  • $\begingroup$ There are a lot of things we do now that we are not evolved to do. Like make fire. Your species might be using its brain and tech to gain access to habitats and resources that were not available to its recent ancestors. $\endgroup$ – Willk Jan 11 at 23:59
  • $\begingroup$ @Willk That is the plan, however I specifically want my fictional species to have access to living in deeper waters long before they develop pressurised habitats, something that is expensive and dangerous even for modern day humanity, and therefore they would have to be able to breathe under high atmospheric pressure. $\endgroup$ – FrankRebin Jan 12 at 0:21
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    $\begingroup$ Your next question: how might diving animals that breathe at deep atmospheric pressure be intrinsically protected against oxygen toxicity? Because I bet they are! I have an answer in mind, but if you post the question I will wait to see if one of the others comes up with the same answer. $\endgroup$ – Willk Jan 12 at 0:33
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Degas the water by heating it.

Gases dissolve in water. Fish count on that. You can get the gas out by heating the water. When you boil water, the initial bubbles that are made are from dissolved gas coming out of solution.

In your moonbubble room you have a heating element. You heat water and capture bubbles released. Fresh water brings new gas which you release and add to the bubble. This is energy intensive because water soaks up a lot of heat. But not as energy intensive as schlepping a big bubble down from the surface!

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  • $\begingroup$ This is a good alternative for getting the air down there! However I'm not sure not sure how you could continuously maintain this without having a 100°C house. $\endgroup$ – FrankRebin Jan 12 at 11:15
  • $\begingroup$ @FrankRebin - the same way you heat your house without walking around open flames. You would have a boiler equivalent below the building (though of course you do not need to boil the water!). Dissolved gas liberated from water in the boiler will bubble up thru a channel leading to the bubble room. Spent hot water would be used to warm the dwelling, or discharged and heat incoming water via a counter current mechanism. $\endgroup$ – Willk Jan 12 at 16:36
  • $\begingroup$ Thats quite a good idea! But doesn't the water need to be boiling to efficiently and quickly liberate the air so you don't need a massive volume of water to sustain multiple occupants breathing? $\endgroup$ – FrankRebin Jan 12 at 17:43
  • $\begingroup$ @FrankRebin - the water does not need to boil. Dissolved gases leave solution before then. You can do an experiment and make ramen at the same time. Get a saucepan and boil water. You will see bubbles form at the bottom of the pan. They will not be going much,. Those are dissolved gases. Go ahead and let the water boil. Then turn off the heat and add some ice to cool it quick. When you heat it again those lazy bubbles will not form. There is no gas left in the water because you drove it off. The first ones will be the water vapor and those bubbles act differently. Now make ramen. $\endgroup$ – Willk Jan 12 at 18:08

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