4 ms·

My take would be that underwater temps cannot get below freezing. So the surrounding temperatures above water can be lower than under water.

nh23423fefe 2mo ago
plus thermal conductivity of water vs atmosphere
mrloopex 2mo ago
Freezing point of water changes with salinity and impurities. By definition a liquid cannot be below its freezing point until it has completed its phase change.
- FromHoiPolloi 2mo ago
  Yes. My point was that it's easier(?) to get below freezing point above water than below. So while the cold air keeps the upper part of the iceberg (relatively) intact - it will slowly melt below the sea until the center of gravity changes enough to flip over.
- RetroTechie 2mo ago
  > By definition a liquid cannot be below its freezing point until it has completed its phase change. Supercooled water is a thing: (and I've seen it a few times myself) https://en.wikipedia.org/wiki/Supercooling https://en.wikipedia.org/wiki/Supercooling
  - wahern 2mo ago
    Superheating, too, and that's something that can happen in a microwave, occasionally causing severe burns when superheated water flash boils. AFAIU, it's the same phenomenon--lack of nucleation sites to kick-off the phase transition.
  - mrloopex 2mo ago
    Does that mean every TTT diagram is wrong? Nevermind I just learned about CCT diagrams. I guess having only one year of materials engineering means I should STFU. :)
Pooge 2mo ago
> My take would be that underwater temps cannot get below freezing Yep, density of water changes with temperature—it's the only thing that has that phenomenon—and therefore the colder water is always at the surface. That's actually what made life possible since life could survive despite a frozen surface. Happy to be proven wrong, but that's what I learnt making cocktails and investigating clear ice :)
- dotancohen 2mo ago
  Lots of things change density when temperature changes. Water is unique that below 4°C, it gets less dense as it cools - and that trend continues even through the phase change. That's why, as you mention, ice floats, and the surface freezes first, and fish can live below a frozen surface.
  - Pooge 2mo ago
    > it gets less dense as it cools Right!! Thanks for correcting me.

nh23423fefe 2mo ago

plus thermal conductivity of water vs atmosphere

mrloopex 2mo ago

Freezing point of water changes with salinity and impurities. By definition a liquid cannot be below its freezing point until it has completed its phase change.

FromHoiPolloi 2mo ago
Yes. My point was that it's easier(?) to get below freezing point above water than below. So while the cold air keeps the upper part of the iceberg (relatively) intact - it will slowly melt below the sea until the center of gravity changes enough to flip over.
RetroTechie 2mo ago
> By definition a liquid cannot be below its freezing point until it has completed its phase change. Supercooled water is a thing: (and I've seen it a few times myself) https://en.wikipedia.org/wiki/Supercooling https://en.wikipedia.org/wiki/Supercooling
- wahern 2mo ago
  Superheating, too, and that's something that can happen in a microwave, occasionally causing severe burns when superheated water flash boils. AFAIU, it's the same phenomenon--lack of nucleation sites to kick-off the phase transition.
- mrloopex 2mo ago
  Does that mean every TTT diagram is wrong? Nevermind I just learned about CCT diagrams. I guess having only one year of materials engineering means I should STFU. :)

Pooge 2mo ago

> My take would be that underwater temps cannot get below freezing Yep, density of water changes with temperature—it's the only thing that has that phenomenon—and therefore the colder water is always at the surface. That's actually what made life possible since life could survive despite a frozen surface. Happy to be proven wrong, but that's what I learnt making cocktails and investigating clear ice :)

dotancohen 2mo ago
Lots of things change density when temperature changes. Water is unique that below 4°C, it gets less dense as it cools - and that trend continues even through the phase change. That's why, as you mention, ice floats, and the surface freezes first, and fish can live below a frozen surface.
- Pooge 2mo ago
  > it gets less dense as it cools Right!! Thanks for correcting me.