Conversation so far:
How does water freeze?
Freezing happens when the molecules of a liquid get so cold that they slow down enough to hook onto each other, forming a solid crystal.
How happens to waters molecules when it freezes?
When frozen, water molecules take a more defined shape and arrange themselves in six-sided crystalline structures. The crystalline arrangement is less dense than that of the molecules in liquid form which makes the ice less dense than the liquid water.

Question: Why isn't the bottom of the ocean frozen?
Self-contained rewrite: Why isn't the bottom of the ocean frozen?