Question
Also, when water is cooled, it first contracts in volume like other liquids but below ${4^\circ }C$ it starts expanding and continues to do so till the temperature reaches ${0^\circ }C$, the point at which water freezes into ice and when ice is formed, density reduces.
Therefore, from above we can conclude that the main consequence of variation of density of water with temperature is that water has its highest density at ${4^\circ }C$. So, at low temperature in the ocean, top layer of water freezes into ice but the water below this layer will remain in liquid form which allows the existence of aquatic species even in cold regions.