Here’s the kicker: salt lowers the freezing point, a process called freezing point depression. Think of it like this—salt ions get between water molecules, making it harder for them to cozy up and form ice crystals. So your seawater has to get extra cold before it gives up.
This is why we dump salt on icy roads in winter. Same principle: salt melts ice by yanking the freezing point down. Irony much? On roads, salt fights ice; in the ocean, salt delays it.
Why doesn’t the whole ocean freeze solid?
Good question, right? The ocean is massive and constantly moving, which spreads the cold around like a bad buffet. But also, once that top layer of salt water freezes, it actually expels the salt—creating pure freshwater ice. That leftover salt sinks, making the water below even saltier and harder to freeze. It’s nature’s little “nope” to total ice domination.
You’ve seen this if you’ve ever tasted old sea ice: it’s not salty. It’s basically a frozen freshwater popsicle floating in brine. Weird world, huh?
The science behind salting roads in winter: How it really works
