Question

The _________ of water enables aquatic animals to survive in a reservoir where the surface layer of water has frozen.

Answer 1

Anomalous expansion of water:

• Water shows unusual or anomalous behavior when it is heated or cooled between $0°\mathrm{C}$ and $4°\mathrm{C}$. All substances generally contract on cooling while water expands. When water is cooled, it first contracts just like other liquids but up to 4°C.On further cooling, it expands instead of contracting. This expansion takes place up to $0°\mathrm{C}$. Thus, at, water has a maximum volume and minimum density.
• This helps preserve aquatic life during very cold weather.
• The top layer of water in the pond contracts, when the temperature falls and thus becomes denser and sinks to the bottom.
• A circulation is thus set up until the entire water in the pond reaches its maximum density at $4°\mathrm{C}$.
• If the temperature falls further, the top layer expands and remains on the top till it freezes.

Therefore, the anomalous expansion of water enables aquatic animals to survive in a reservoir where the surface layer of water has frozen.