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I've been thinking of having an underwater structure in a world with ice, but I would think water from currents would melt the ice. Would there be any way to keep it frozen and have an underwater structure of some sort?

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  • $\begingroup$ So the underwater structure has to be made of ice as well? $\endgroup$ – Spencer Feb 15 at 1:59
  • $\begingroup$ @Spencer That was the goal, to use ice bricks as walls, with maybe stone or clay for floors, or dried wood on the outside of ice for insulation. $\endgroup$ – WolvesEyes Feb 15 at 2:01
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    $\begingroup$ Looking into Brinicles, a naturally occurring phenomenon of underwater ice. $\endgroup$ – Plutian Feb 15 at 9:51
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    $\begingroup$ It might be worth invesitigating how ice lll, V, Vl and Vll behave near liqid water. Making the existence of the ice pressure depend insted of temperature dependent might do something interesting. $\endgroup$ – TheDyingOfLight Feb 15 at 23:14
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    $\begingroup$ It sounds like you want pykrete. en.wikipedia.org/wiki/Pykrete The wood pulp tends to insulate the ice so less refrigeration is needed to keep the ice solid $\endgroup$ – Jim Baerg Feb 17 at 23:13
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Impure Water

Salt water has a lower freezing temperature than distilled water. The freezing point for fully saturated salt water is about -21 C. Other impurities could lower it even further. If the ocean temperature was at -10 C, the salt water would not freeze, but already frozen fresh water ice would not melt.

The bigger problem is how to keep it submerged, because ice floats.

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    $\begingroup$ This was something I read, was that salt water had lower freezing temperatures, but they also use salt to thaw ice, so I wasn't entirely sure if the two could mix. Wood or stone frozen within could help sink it? Or maybe it would cause it to thaw... $\endgroup$ – WolvesEyes Feb 15 at 2:21
  • $\begingroup$ +1 for "ice floats". I think any ice structure would have to "hang" from a surface ice sheet, supported by its buoyancy and building top to bottom. $\endgroup$ – Zxyrra Feb 15 at 2:22
  • $\begingroup$ @Zxyrra Do you think a stairwell to the surface of a frozen ocean, if thick enough, could keep a larger building submerged? Or that stone or other heavy objects could be frozen within? $\endgroup$ – WolvesEyes Feb 15 at 2:23
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    $\begingroup$ @WolvesEyes I'm not sure if a stairwell "could keep a building submerged". You would have to build its structure, then add stairs inside. If the buoyancy of the ice + air is greater than the weight of the structures, you can definitely have stone. $\endgroup$ – Zxyrra Feb 15 at 2:27
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    $\begingroup$ re: Suspending heavier material inside the ice to weigh it down, this would not work as objects do not stay suspended in ice, but instead gradually sink through it. The force the heavy objects exerts on the ice below it melts that ice. This video is demonstrative: youtube.com/watch?v=qQCVnjGUv24 Notice how the wire passes straight through the ice rather than slicing it. $\endgroup$ – Tom O'Daighre Feb 15 at 15:19
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very cold (fresh) water and ice nucleating agents (proteins, etc.) maybe. mix in some endothermic reactions on the inside of the underwater castle to keep things cold enough to maintain the ice (As guideline if you're looking for some reactions, water needs to lose 333.55 kJ of energy per kg of water to freeze 0 degree water into 0 degree ice.)

edit: also is the structure filled with water? because if not, you have to make it strong enough to withstand the pressure of the lake water pushing in against flimsy ol' air.

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Methane clathrates.

methane clathrate outcrop

source: https://www.youtube.com/watch?v=J_kRKR4W8xY

https://en.wikipedia.org/wiki/Methane_clathrate

Methane clathrate (CH4·5.75H2O) or (4CH4·23H2O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Originally thought to occur only in the outer regions of the Solar System, where temperatures are low and water ice is common, significant deposits of methane clathrate have been found under sediments on the ocean floors of the Earth. Methane clathrates are common constituents of the shallow marine geosphere and they occur in deep sedimentary structures and form outcrops on the ocean floor. Methane hydrates are believed to form by the precipitation or crystallisation of methane migrating from deep along geological faults. Precipitation occurs when the methane comes in contact with water within the sea bed subject to temperature and pressure.

Methane clathrates have methane molecules incorporated into water ice. Other hydrocarbon gas/water ice clathrates are possible too. They require cold and pressure. Depicted are the arms of a remote control submarine messing with a piece they found. This ice can accumulate in big outcrops. Interestingly the ice is always covered with life; there is some sort of metabolism going on that I have never seen laid out, probably with methanotrophs at the base who are happy to have their dinner held still for them by the clathrate.

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