Why doesn’t the water freeze under the thick ice?
Water under a thick layer of ice in reservoirs does not freeze due to the weak thermal conductivity of the latter. Thus, ice acts as a heat insulator for water, which maintains a relatively high temperature under its layer. It is also known that the thicker the ice layer, the stronger the frost and the lower the air temperature.
In theory, water in any body of water in winter should completely turn into ice. But in practice, this does not happen. Neither a small lake, the depth of which does not exceed three meters, nor deep-water rivers and seas, never freeze to the very bottom, no matter how severe the winter may be. How can this phenomenon be explained? The thing is that ice has the ability to protect water from hypothermia. To understand all the nuances of this phenomenon, you first need to figure out exactly how the water is cooled.
When the water masses reach a temperature of + 4 * C, the layers of the reservoir begin to move intensively. Cold layers, having a lower density, rise to the top. Warm, denser masses remain at the bottom. Water layers that are cooler and closer to the surface turn into ice. It gradually fetters the entire surface of the reservoir. The wind can no longer mix the water that remains under the ice. And therefore all layers remain unchanged, especially in places with stagnant water and slow currents. It is due to the low thermal conductivity that the ice that forms on the surface of the reservoir prevents it from freezing to the bottom.
In theory, any of the four oceans can freeze to the bottom. But this will only happen if the thermometer drops to the minimum mark, and the core of our planet will cease to be active.
In reality, only shallow water bodies and puddles completely freeze through. In very cold winters, water turns into ice to the very bottom only in shallow lakes and ponds. Under normal conditions, at moderately low temperature indicators, the water that is under the layer of ice will always maintain a slight positive temperature.
