Cold

by Bill Streever

  The fact is that some of the winter-active animals do more than tolerate the seasonal cold. Some thrive. Lemmings, for example, are known to mate and reproduce in their subnivean tunnels. They have snowbound orgies and fill their tunnels with young, thumbing their noses at winter. The young will themselves be old enough to breed and reproduce and raise their own offspring within weeks of being born. Some will be born and reach adulthood before the spring thaw, when they will see for the first time the light of the sun and feel for the first time the warmth of a summer day.

  And there is food in the snow, food for lemmings and voles and shrews. There is a food web here in these subnivean chambers that humans seldom suspect. Between the ground and the snow, through the winter, there are fly larvae, beetles, millipedes, fungi, and bacteria, all of them working over the dead leaves, roots, and branches of the previous summer. Spiders and centipedes and bigger beetles eat the fly larvae and millipedes and smaller beetles. The shrews and lemmings eat anything big enough to draw their attention. This is no desert. This is not some cave with only one or two species. In Canada, a scientist poking around in the subnivean world found nineteen species of spiders, fifteen species of mites, sixty-two species of beetles, sixteen species of springtails, thirty-two species of ants and wasps, and two species of centipedes, all of them active, living under winter snow.

  And there are seeds. From William Pruitt’s Wild Harmony: The Cycle of Life in the Northern Forest:

  The new snow covered the layer of birch seeds and hid them from the small birds. The added weight of the fresh snow compacted the middle layers of the api [snow cover]. As the crystals squeezed together and broke, the cover creaked and groaned. A foraging vole would stop and huddle, ears twitching, and then resume its errand. The sounds breached the even tenor of life under the snow. An additional disturbance was the faint scent of birch carbohydrate that occasionally filtered down from above. Some voles dug upward through the layers of snow. One layer was easily tunneled, the next was harder; no two were alike. When a vole reached the seed-rich layer, it drove a horizontal drift along it and devoured every seed.

  The tunnels are not without danger. They can freeze over with ice crust, becoming impenetrable. Carbon dioxide can build up. When warm snaps and chinook winds melt the snow and send floodwater into the tunnels, voles and lemmings and shrews can drown in their chambers. And if there is not enough snow, if the world grows cold before the snow grows thick, as often happens, the subniveans freeze to death, or starve trying to stay warm, or, as is closer to the truth, starve and freeze to death and succumb to disease simultaneously, like Greely’s men and De Long’s men and Bering’s men.

  The interactions between animals and their environment do not flow in a single direction. As the first line of a poem affects the last and the last line affects the first, the environment affects animals and animals affect the environment. Subnivean winter actives change the nature of the snow, creating caverns for meltwater in spring. Above the snow, foraging hares and caribou and moose change the nature of their forage. Along rivers, hares eat willows, and on higher ground they eat birch saplings. This winter feeding can be intense enough to control the structure of the forest, as if the animals are farming the trees, keeping them small and as succulent as possible year after year. But the plants fight back. Invisibly, the plants produce compounds that deter winter grazers. The paper birch makes papyriferic acid. In succulent juvenile plants — plants that appear juicy and tasty — the acid may be twenty-five times more concentrated than in adult trees. At times, it forms droplets on the winter twigs of saplings. Captive hares, offered birch twigs with naturally high concentrations of papyriferic acid, stopped eating. There is reason to believe that the coming and going of some hare populations, usually blamed on hungry lynx, may be a result of chemical defenses in plants. As the hares graze, the plants produce more of the compounds that deter grazing, becoming less edible, and the hares die back. With fewer hares and less grazing, the plants become more edible, and the hares grow more abundant.

  Winter for hibernators is safe; for bears, as few as one percent might die in their dens. Winter for winter actives is dangerous. It is not the single cold spell that kills a caribou or a moose, but rather the additive effect of cold spells and snowstorms and missed meals, or even the effects of one winter adding to the next, with summers too short for the animal to recover fully. One summer, they are a bit on the slim side, the next summer they have slimmed down a bit more and do not reproduce, and that winter they die from starvation or disease or, too slow to escape, from a set of teeth ripping through the jugular or crushing the skull. A pack of wolves can consume a moose every few days. The wolves will also eat caribou, beavers, hares, voles, and shrews. Shrews are also subject to attacks by weasels and owls. While a shrew hunts bugs under the snow, an owl or a weasel or a fox hears the commotion and crashes through from above, bringing sudden daylight and death into the tunnels below.

  Winter actives must deal with humans, too. Snowmobiles and skiers spook the animals, pushing them into an energy-wasting run. Fences prevent them from reaching better grazing. Roads make convenient corridors for winter movement, luring animals to death by unexpected impact. In Wyoming, in 2004, a vehicle ran through a herd of pronghorn, killing 17 animals. In 2006, it happened again, another vehicle in a different place killing, coincidentally, another 17 animals. Railroads, too, make deadly corridors. A train heading west through Wyoming one winter ran through a herd of winter-active pronghorn, rendering 125 of them suddenly and permanently inactive, dead on the tracks.

  It is December tenth and thirty-seven degrees in Whittier, Alaska. Six inches of slush cover the parking lot, and rain falls at a slant, carried by wind. I am wearing a dry suit, a scuba tank, and thirty pounds of lead. Under my dry suit, I wear two nylon T-shirts, a wool sweater, sweatpants, thick socks, and coveralls made of Thinsulate. Three-finger mitts, a quarter of an inch thick, cover my hands. The water is thirty-nine degrees, two degrees warmer than the air. A sea otter swims on the surface, watching me dive. Below, stunted kelp dusted with glacial sediments grows on rocks and gravel. On the seabed, spot shrimp dart about between rocks. Multiarmed starfish crawl around on their tube feet searching for shellfish. At eighty feet, I swim through a field of pale sea whips, a cold-water soft coral that grows in vertical ropes rising six feet from the bottom. The stalks are covered with tiny eight-armed polyps. Nearby, two copper-colored rockfish sit on the bottom, thick finned, huddled in depressions in the mud, as if trying to stay warm. The kelp, the shrimp, the star-fish, the corals, and the fish all have enzymes that work reasonably well in thirty-nine-degree water. I do not.

  Dry suits always leak. They are not dry suits so much as damp suits, with water sneaking in through the wrist and neck seals. Moisture leaves my arms and chest clammy. At twenty minutes, my hands are numb. The blood vessels in my fingers, especially near the skin, have squeezed shut, dropping the blood flow to ten percent of normal, conserving heat for my core. I can still use my mitted hands to work my dry suit valves, but it is increasingly hard to move individual fingers. My air consumption increases. At forty minutes, my hypothalamus, buried deep in my brain, somewhere behind my nose, triggers shivering. As a rule of thumb, shivering starts when the core temperature drops to ninety-seven degrees, two degrees below normal. Muscles contract and relax in an effort to generate heat, cycling six to twelve times every second, burning glycogen like there is no tomorrow, generating four times more heat than the body at rest. When the glycogen is gone, the shivering stops. Or if the body temperature drops to about eighty-eight degrees, the shivering stops, and then, in all likelihood, there is no tomorrow.

  I try to think warm thoughts. I repeat the mantra “I am warm. I am warm. I am warm.” In fact, I am not. The mantra fades, and I think of Laurence Irving’s airman, experimentally exposed to the cold, shivering so violently that Irving worried that he might shake himself apart. I am abject and miserable, wishing that I had the blood of one of Darwin’s Fuegi
ans. I think of my caterpillars, Fram and Bedford, lying curled up in my freezer, frozen solid. I envision a ground squirrel in its hibernaculum, shivering when its body temperature drops below freezing, warming up and then drifting back into the stupor of cold in a cycle that repeats itself through the winter. And then there is Apsley Cherry-Garrard, writing of the relative warmth of fifty-five degrees below zero.

  The U.S. Navy Diving Manual has this to say:

  Hypothermia is easily diagnosed. The hypothermic diver loses muscle strength, the ability to concentrate and may become irrational or confused. The victim may shiver violently, or, with severe hypothermia, shivering may be replaced by muscle rigidity. Profound hypothermia may so depress the heartbeat and respiration that the victim appears dead. However, a diver should not be considered dead until the diver has been rewarmed and all resuscitation attempts have proven to be unsuccessful.

  For navy literature, these might pass as reassuring words: you are not dead until you are warm and dead.

  The manual also warns that regulators can freeze underwater, dumping the diver’s air supply in a steady free flow. And it says, in one understated sentence, that “hypothermia may predispose the diver to decompression sickness.” At any temperature, under pressure, nitrogen in the diver’s air supply dissolves in the blood. If the diver surfaces too quickly, the nitrogen leaves the blood as bubbles, damaging tissue and blocking capillaries. The results can mirror those of a stroke: pain, numbness, paralysis, loss of memory, dizziness, death. But low temperatures increase the solubility of nitrogen, so the cold diver takes on nitrogen more quickly. Worse, as the diver grows colder, constricted blood vessels in the hands and feet do not allow the blood flow needed to flush dissolved nitrogen efficiently. Worse still, it quickly becomes too cold to seriously consider a slow ascent or a decompression stop. By now, though, I am too cold to focus on any of this. The thoughts just pass through my mind, as if part of a dream. I am dangerously cold to be underwater. I signal my dive partner that it is time to head up.

  I am soft. The ama divers of Japan and Korea would find my softness amusing. For more than a thousand years, they have picked up seafood, diving on a breath of air. For a brief period, they dove with helmets and canvas suits, but they saw that this sort of diving would soon exhaust the fishery. Rules emerged that restricted divers to a breath of air. In most places, an ama can wear nothing warmer than a partial wet suit. The thinking is that only the toughest and most skillful divers should succeed. They work in water as cold as fifty-seven degrees. At this temperature, softer people are exhausted or unconscious within two hours, and predicted survival times are less than six hours. The ama often work for three or four hours at a time. Almost all of them are women. Men, it is said, cannot handle the cold. Some of the ama dive into their seventies. They are not demure. They have a reputation of independence, of rude language, of loud voices. An anthropologist who once lived and dove with the ama remarked on their swearing and summed them up by describing their means of greeting one another: they would say, in Japanese, “Yo!” instead of “Hello.” The ama, she wrote, stay in the water as long as they can, becoming at least mildly hypothermic on a daily basis. They return to shore and huddle inside their amagoya warm-up shed. The anthropologist wrote of returning to the amagoya one afternoon. The ama were withdrawn and sullen after an unsuccessful day in the water. It was raining. Everyone was cold. As they warmed up, they began to laugh and joke. Two of them put on costumes to entertain the others. “You see,” one of them told the anthropologist, “if we laugh we can forget how damn cold it is!”

  They would laugh at me now, with all my gear and still shivering, a weak American male. If I become much colder, it will be difficult to hold this regulator in my mouth. When I reach the surface, the first thing I see is a small waterfall, flowing over the edge of a bluff and falling twenty feet into the ocean. The water flows from beneath a sheet of melting ice surrounded by spruce trees, their boughs heavy with slushy, dripping snow.

  In the water, large whales are less like me and more like moose and musk oxen: they are as susceptible to overheating as they are to hypothermia. Water sucks away heat thirty times more quickly than air, but the large whales wear a coat of blubber, far more than a sweater of fat, more like a down coat without zippers, permanently affixed. A matrix of collagen gives blubber a spongy structure that yields to pressure but does not sag or jiggle like the fat of obesity. The stuff has the thermal conductivity of asbestos. In mammals with thick coats of fur, the temperature rises between the outside of the coat and the skin. But the skin of a whale is close to the temperature of the water in which the animal swims, with the temperature rising only within the blubber, closer to the inner furnace of the whale. In the bowhead whale — a sixty-foot-long baleen whale of the far north — the blubber can be more than two feet thick. Outside, when the whale swims between and beneath ice floes, and when it surfaces to breathe through cracks in the ice, its skin temperature could be close to freezing, but inside the temperature holds close to ninety-six degrees. And the blubber is vascularized, with shunts that control the amount of blood reaching the skin. The shunts open when the whale gets hot and close when it gets cold.

  The blubber is more than insulation. It streamlines the body, and near the dorsal fins and in the tail the blubber may act as a bio-mechanical spring, storing and releasing the energy needed to flap huge flukes through thick water. The blubber floats the whale, like an enveloping inner tube, like a diver’s buoyancy compensator.

  The bowhead whale’s food generates the heat that the blubber protects. The whale swims through the water with its mouth agape, or skims the surface, or occasionally takes a mouthful of mud. With its tongue, it squeezes the mouthful of liquid oozing with mud and crustaceans and larval fish outward through the baleen combs that look like black, feathery plastic teeth. This is not just any tongue, but rather a tongue of tongues, fifteen feet long and ten feet wide. The tongue squeezes out the water and then sweeps across the bristles of keratinous baleen, the combs that pass for a sieve of teeth lining the whale’s giant mouth, combs that may remind one of teeth but that in fact evolved from the ridges commonly found running along the roof of the mammalian mouth, including the human mouth.

  The bowhead, despite its blubber, loses something like ten thousand calories each day to the cold. The crustaceans and fish and mud that the whale scoops from the sea are not pure fat. To get the fat it needs, the bowhead requires a hundred tons of food each year to stay warm, plus that much again for growth, movement, and the making of little whales. To complicate matters, the bowhead feeds for the most part during the summer and autumn, when it may consume as much as two tons of food in a day, then diets through the winter and early spring, when food is less abundant.

  For bowhead whales, the cold is not just the cold — it is ice. Swimming beneath the ice is no small risk for an air breather. At times, the bowhead dives between openings in the ice, holding its breath, perhaps following bubble trails left by predecessors, or looking for light penetrating down from above, or following the low-pitched rumbling calls of its brothers and sisters and parents and cousins as it makes its way sometimes for more than a mile between surfacings. At other times, it follows leads in the ice, long openings between two ice floes, that, as any Arctic explorer will tell you, can close with little warning. Inupiat hunters say they have seen bowheads break through ice two feet thick. Scientists, who in comparison to Inupiat hunters are laughably ignorant of the way of the whale and spend far too little time on the ice to see what is really going on, have documented bowheads bashing through ice seven inches thick. And the whales have another trick: they can find a tiny airhole and then push the ice upward, not breaking it but merely forming a hummock, a bump on the surface, into which air is sucked and from which the animal breathes.

  Also swimming under the ice are the much smaller narwhal and beluga — the tusked whale and the small white whale of the north, both toothed whales more akin to dolphins than to the mighty cr
ustacean-and-mud-eating baleen whales. The narwhal has been found within three hundred miles of the North Pole, and the beluga within six hundred miles, relying on open leads in the ice for air.

  There are seals, too, out on the ice. The ringed seal is found as far north as the North Pole, living in winter beneath and in the ice, using its foreclaws to scrape away breathing holes, maintaining bigger openings that lead to snow caves where the animals give birth and nurse their young. In spring, they climb out on the ice to bask in the sun and to shed their fur and replace it with new fur. They have blubber, but they also rely on fur for warmth. The individual hairs of seal fur are flat, not round as they are in most carnivores. The flatness lets the hair lie down, streamlining the animal as it swims.

  And there is the sea otter — blubberless, but with more hair per square inch than any other animal alive. Shave a square inch of sea otter, and you will have to sweep up nearly a million hairs. Its hairs trap a layer of air, and the otter, though living in water, is never quite wet. It wears a dry suit that actually stays dry. In exchange, it spends more than one hour in ten preening, combing, and grooming. It sometimes lies on the surface, belly up, its nose and paws — unprotected by the fur that covers its body — held out of the water for warmth. And like whales and seals and birds and to some degree even humans, the sea otter isolates the warm blood of its core from the cold blood of its extremities with a rete mirabile — literally, a “wonderful net,” a mesh of veins and arteries. The mesh is a heat exchanger. Arteries carrying warm blood from the core are surrounded and interwoven with veins carrying cold blood from the extremities. Before the warm blood hits the extremities and gives up its heat to the outside world, it warms the cold blood that is moving back from the extremities toward the core. Heat is conserved. Calories are saved.