Before I read all of the posts in the thread, I assumed that pond, lake and sea ice wouldn’t exist at all. I figured that as ice first began to form at the water-air interface, with the air being colder than the water except at the interface, that sinking ice would melt in the warmer water below the surface. Is the part I’m missing that the sinking ice would cool the water below enough to eventually freeze it all?
I think so - and in particular, when it melts, the phase change itself requires a heat input, so it would cool the water more because of that.
Well, if cold water is denser than warm water, and the surface is cold enough to freeze, the ice should, in theory, sink into colder water.
But ice has a fairly high albedo. If it typically sank, I would think that the surface water would still be absorbing heat from the sun. I would think that ice would have to mostly form at the bottom layers of lakes and seas, and stay down there. Bodies of water would typically not freeze solid, as the water on top would be getting sunlight during even short days (except at the poles).
It sounds pretty complicated to model. Like, what if the chemistry of the atmosphere was such that water vapor was heavier than the air?