How do marine mammals avoid freezing to death? Do they ever feel cold?
—“Disputatore” via Twitter
D. Ann Pabst, a marine zoologist at the University of North Carolina Wilmington, bundles up a reply (as told to Coco Ballantyne):
Marine mammals maintain a warm core temperature in frigid water with two broad types of responses: behavioral and physiological. A typical behavioral response is migration—in the winter, for instance, pregnant right whales migrate from waters off Canada and New England to the warmer coastal waters of Georgia and Florida to birth their young. Physiological adaptations, on the other hand, include having a large body size, as most marine mammals do, which means a relatively low ratio of surface area to volume. (As size increases in a three-dimensional object, the object’s volume grows at a faster rate than does its surface area.) By having a small area of skin, across which heat is exchanged with the environment, as compared with a large volume of heat-generating body tissue, big mammals can retain their heat more effectively.
Marine mammals also have excellent insulation in the form of fur or blubber, or both. The sea otter has the densest hair of any mammal known: 130,000 hairs per square centimeter of skin, by one count. Fur insulates most efficiently when it is dry because it traps still air, an excellent insulator, against the skin surface. Water, in contrast, is highly conductive; it removes heat from the body 25 times faster than air at the same temperature. The otter’s fur is so dense that it can trap a layer of air at the skin surface even when the animal is submerged.
Mammals that spend most or all of their life in water rely on blubber—a specialized layer of the skin containing fat as well as the proteins collagen and elastin—which provides, among other things, insulation and energy storage much as human fat does. The amount of blubber varies from one animal to the next. Newborn harbor porpoises pack the most; some 43 percent of their total body mass is blubber.
In some circumstances, marine mammals suffering from poor nutrition or health might have trouble maintaining a healthy blubber supply, both in terms of quantity and quality. These animals may ultimately die from exposure to extreme temperatures. Alternatively, if they find themselves displaced from their natural habitats, they might succumb under the strain of conditions to which they are not suited.
The skin of marine mammals is innervated with temperature-sensing nerve cells just as is the skin of any mammal. These specialized creatures certainly have the ability to sense temperature, and they clearly respond to temperature stimuli, but how that translates into what they feel—whether they experience discomfort, for example—is a difficult question to answer.
How does bathwater well below the boiling point give off steam?
Herman Merte, a professor emeritus of mechanical engineering at the University of Michigan at Ann Arbor, explains:
What one sees drifting above a hot bath—often called “steam”—is in fact tiny drops of liquid water that have coalesced out of the gaseous mixture of air and water vapor above the fluid’s surface. The vapor, itself an invisible gas, arises from evaporation, whereby water molecules escape from a liquid. Evaporation is a slower process than boiling but is accelerated when water heats up (gaining increased energy).
The conditions under which invisible water vapor condenses into visible mist depend on the ambient temperature and the amount of water vapor in the air. Compared with cold air, warm air can hold more water vapor before becoming so saturated that condensation occurs. This property explains why a bath—or a cup of tea—emits more visible steam on a cold winter morning than on a hot summer afternoon.