Sperm Whale (Physeter catodon)

The tasty titbits that sperm whales savour over live in deep water. To swim that deep, they have to be able to withstand huge buoyancy forces. To enable sperm whales to dive into the depths, nature found a solution: It gave sperm whales a 2,000 kg spermaceti, found in the whale’ head, that is lighter than water at body temperature. By letting sea water flow in, the spermaceti cools down, and its density becomes greater than the density of the water.
This enables the whale to dive down. To rise again, the whale pushes the sea water back out and increases the flow of blood to the head. The spermaceti warms up again, and the whale rises to the surface of the water.