Question

How can the freezing of surface waters make the water that is left unfrozen denser

Answer 1

this is because water expands as it gets cold hence floating leaving the unfrozen water dense

Answer 2

Step-by-step explanation:

When an aqueous solution freezes, the unfrozen solution becomes denser. That's because some of the water has been removed as ice. However, the solutes remain dissolved in a solution with a smaller liquid volume. The concentration of the solution increases, so the density increases.