Why is it important to ensure that the ice is melting as the temp is taken?

Water in its solid state, produced by freezing. As the water in lakes and seas cools, it becomes heavier. The lighter, warmer water is displaced by the heavier water and rises to the top. But when the water as a whole reaches about 4° C. (39° F.), this process reverses. The water becomes lighter as it nears the freezing point and remains as a layer above the warmer water beneath. This upper layer then turns to ice, “makes itself compact.” Being lighter than water, the ice keeps the waters beneath “hidden as by stone,” protecting marine life. Were it not for this phenomenon, much of the water in the lakes and even the oceans would in time become solid ice, making the earth inhospitable to life.
Jehovah God called Job’s attention to the marvel of ice, the Almighty saying: “Out of whose belly does the ice actually come forth . . . ? The very waters keep themselves hidden as by stone, and the surface of the watery deep makes itself compact.” (Job 36:1; 37:10; 38:1, 29, 30) The formation of ice as here referred to is possible only because of a most unusual property of water. As mentioned above we can understand as the water in lakes and seas cools, it becomes heavier.
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