For liquids where the solid doesn’t float, how does the liquid freeze?

Question

Take for example water; when water freezes, ice floats, and given a pond or something during the winter, the pond seems to freeze from the top down.

Considering a similar circumstance, let’s say we had an identical hypothetical liquid but where ice didn’t float, how would the pond freeze? Since all the near-freezing/ frozen material sinks, I would imagine it freezes from the bottom up, but would the same pond that only partially freezes top down also just partially freeze bottom up, or would it freeze more since when a pond freezes top down, it essentially separates the liquid water from the cold atmosphere?

I also recognize that another scenario might be possible if taking into account sunlight and how that would affect things, but for the sake of the question let’s ignore that and say that the atmosphere is at a fixed temperature on a cloudy day such that the top-bottom freezing pond freezes only partially (e.g there is liquid water under the ice in a stable state)

Answer 1

As you mention, solid form will sink to the bottom.

Ponds freeze because heat moves from the water into the air. When the surface freezes, the insulation of the ice layer decreases the heat transfer. Further freezing happens at progressively slower rates. Deep lakes cannot freeze completely in single season.

If the solid form is denser, then there is no change in heat transfer after some freezing starts. It is likely that more of fluid can freeze since the warmest portion stays on the top.

Further, such ponds would have a more difficult time thawing. Any warming of the fluid on top would have little interaction with the frozen material below. Ponds might thaw only down to a couple of meters even in the summer.

Answer 2

Heat flows from hot to cold and flows fastest where the difference in temperature is the greatest. So lets imagine an unfrozen lake of water where the air temperature has quickly dropped to a temperature much lower than the freezing point. In this scenario, heat will flow from the surface of the water to the air (since the greatest temperature difference will always be at the surface until equilibrium is reached) essentially lowering the temperature of the water from the surface inward. So ice will always form at the surface whether it floats or not. If the ice sank when it cracked it would speed up the time it takes for the system to reach equilibrium and all the water to freeze. Note that I am ignoring any thermal effects from the ground surrounding the lake.