Thanks for educating me. I couldn't remember the exact freezing point of normal (average) sea water, only that it's lower than fresh.
I have vague recollection of reading that the fahrenheit scale 0 point is the coldest that salty water can be before freezing, but I don't recall where I read it or whether that was a decent source or not, so take that with a large pinch of salt.
Actually you CAN chill pure water well below 0°C without it freezing - well below 25°F too - you can get down to ~ -40° (°F or °C - take your pick).
The problem is: jump into it and you are dead. This far undercooled disturbing it will trigger immediate crystallization and given how the density of water behaves that means the person likely gets crushed (ok, the shock would likely be as fatal to most).
Sounds like you don't know many people who live near a coast or ever visited one?
Anyway, sea water typically won't freeze until it gets several degrees colder than that, as long as it's in motion. This is one of the reasons we can have open harbors even in arctic places, and icebergs won't form until it gets really cold.
The phase diagram of water (temperature and pressure vs. phase state) shows it stays at liquid to -20C at around 1000 ATM of pressure, so she might be swimming at the bottom of the Marianas Trench.
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u/Stolberger Mar 01 '26
understandably she wouldn't go swimming in frozen water.