How does water temperature change as you move from the ocean floor to the surface?
It starts off cold on the ocean floor to warm at the surface.
For this explanation, it's more useful to work top-down rather than bottom-up. At the surface, it's the place where the sun rays actually hit the water, so they are able to receive more heat than the water down below. As you go down deeper, less water is able to receive the heat from the sun or other sources, so naturally they would be cooler than the water at the top. Of course, warm ocean water can still feel pretty cool to us humans, though it may feel like a sauna to the aquatic creatures that reside in the oceans.