Cold

by Bill Streever

  Spring came to the Pleistocene Ice Age about ten thousand years ago. Prior to the start of this recent interglacial, two great ice sheets and many smaller ice fields and glaciers stretched across North America during a period of glaciation that lasted a hundred thousand years. Today’s Beloit Glacier in Prince William Sound is to those ice sheets as a lemming is to a woolly mammoth. During the periods of extensive glaciation, the sites of what would become Chicago, Seattle, Boston, Cleveland, and Kansas City were perpetually snowed in. Just to the south, there was tundra, and to the south of that, forests and grasslands that were stocked with horses and small camels and mastodons. Ground sloths the size of elephants lumbered about, hiding from saber-toothed tigers and American lions. The short-faced bear stood more than five feet tall at its shoulders. Reared up on its hind legs, it stood twelve feet tall. It has been said that the presence of this bear slowed the movement of humans across the Bering Land Bridge, a now drowned stretch of land also called Beringia.

  Even during the coldest periods of the Pleistocene Ice Age, some areas were surprisingly ice-free. Mountaintops stood above the ice. Along the east and west coasts of North America, certain mountains blocked the moving ice sheets, leaving shadows of open but sparsely vegetated ground. Strangest of all, most of interior Alaska, too dry to generate massive quantities of snow, was free of the glaciers that blanketed most of northern North America. Alaska was windswept and brutally cold, but not entirely buried in mile-thick snow and ice. And Alaska did not look like Alaska. With so much of the world’s water tied up in ice, sea level was three hundred feet lower than it is today, and the Bering Land Bridge, as ice-free as the rest of the state, joined North America and Russia. What is now St. Paul Island, a lonely postal address in the middle of the Bering Sea, was then a low hill in what was likely a grassy plain. But the grassy plain did not look like today’s grassy plains. Instead it was a mix of Arctic tundra and modern grassland, sometimes called the Arctic steppe. In its abundance of wild animals and in their variety, the Arctic steppe resembled the Serengeti.

  Wildlife in Beringia, on the Arctic steppe, was not the same as that found south of the great ice sheets, but it was similar. Mammoths wandered in the grass with musk oxen, bison, elk, grizzly bears, and Dall sheep. During the warm interglacial periods that came and went during the two and a half million years of the Pleistocene Ice Age, the corridors joining north to south would open like icy gates, letting animals through from each direction. But if the warmth stayed too long, sea level would rise and flood Beringia, closing the watery gate between Asia and America. The Beringia gate closed each time the sea rose to within 125 feet of its current level.

  The camel and the horse, both products of North American evolution, found their way north and eventually into Asia while the gate was open, and later went extinct in North America. The gray wolf found its way east from Europe and then south, where it met its much bigger and now very much extinct distant cousin the dire wolf. Deer and sheep may have arisen in the old world and crossed to the new via Beringia. Each time the gates closed, the animals locked in on either side would evolve on their own.

  The ice gates — the massive glaciers and snowfields — separating north from south opened and closed to some degree in concert with the Beringia gates. The animals south of the ice evolved differently than those north of the ice, developing esoteric differences. The bison of Beringia had two shoulder humps and long curved horns, while the bison south of the ice had a single hump and shorter horns. At one time, the grizzly bear may have been found only north of the ice, while the black bear may have been found only to the south. The Dall sheep was found to the north, while the bighorn sheep was found to the south.

  The ice created its own weather. Wind whipped off the edges of the ice sheets. Where ice sheets met the ocean, they chilled the water, powering currents. Warm air meeting the ice cooled, and its moisture fell out as snow. Air blowing into the interior of the sheets tended to be sucked dry. Over time, the interior ice sheets thinned, snow-starved. During the Pleistocene Ice Age — the most recent ice age, the one that is dying now, choked by greenhouse gases — spring came and went repeatedly. Each time that metaphorical spring came to the earth, the ice would retreat, biding its time through a millennial summer and then advancing again. And each spring, in retreating, the ice would dump its water into the sea. Sea level would rise reasonably quickly.

  The land rose, too. Relieved of the weight of ice, the land, for ages pressed down by the sheer mass of the ice it had carried on its shoulders, would rebound. Areas would flood with the rising sea level and then emerge, springing upward with the burden of ice removed. Dry pastures and hilltops and mountainsides would emerge with fossils of shells, fish, crabs, and in at least one case kelp, all speaking of a time when they were flooded by cold water.

  The Canadian ecologist Evelyn Pielou put the timing of the Pleistocene Ice Age in perspective. “To make the relative lengths of enormous stretches of time easy to visualize,” she wrote, “let us use as a model one decade to represent the past billion years.” That would make the earth about forty-five years old. “On the scale of the model,” Pielou continued, “a glacial age lasts a month or two.” One great ice age occurred seven or eight years ago, and another just two or three years ago, when the continents shifted into position to separate the steady warmth of the tropics from the seasonal cold of the far north. Each lasted a month or two, until the continents could drift a bit, opening a gate through which warm currents could carry warm water north and cold currents could dump cold water south. The Pleistocene started last week. Things seem warm now, with the great ice sheets pulled back and no more than a patch of snow covering Greenland, another over the North Pole, another to the far south, and a few scattered snowfields and glaciers here and there. During this last week, the ice has expanded and pulled back and expanded and pulled back again and again, at least nineteen times, responding to the level of carbon dioxide in the atmosphere, the liveliness of the sun, and the Milankovitch cycle of an always changing tilt in the earth’s axis and a stretching out of its orbit. If greenhouse gases do not kick this cycle out of kilter, as they almost certainly will, the next expansion of the ice is only minutes away. Minutes being, of course, thousands of years.

  An hour ago, spring came to the Pleistocene. At first, the ice sheets thinned without pulling back. The thinning ice dumped water into the oceans. Sea level rose. The shoreline of northern North America was for the most part one long stretch of tidewater glacier. But then the ice sheets pulled back, melting at their edges. The earth’s surface, relieved of all this weight, rebounded. Bay bottoms and coastal waters became mudflats and then salt marshes and then forests. What is now Lake Champlain between New York and Vermont was then part of the Champlain Sea, which covered Ottawa, Montreal, and Quebec City for two thousand years — actual years, not the fast-forwarded-model years needed to put vast lengths of time into perspective, but two thousand winters and summers, twenty centuries. Its early shorelines were cliffs of ice. Bowhead, finback, and humpback whales swam between those shorelines. Harbor porpoises frolicked about. Ringed seals basked on the frozen surface in early spring. As those two thousand years went on, the land rebounded. The Champlain Sea drained, leaving little more than Lake Champlain, the fossils of whales and seals and cold-water clams, and isolated patches of beach grass and sea rocket far inland from the Atlantic. The same pattern happened all along the coast. In Maine, Augusta and Bangor rose up from underwater. The now extinct Tyrrell Sea shrank to become Hudson Bay, surrounded by rows of terrestrial beach terraces that speak of a former glory.

  On land, retreating ice left barren ground, scraped of all vegetation, covered with rock rubble and piles of boulders and stones ground into flour. Wind sliding down the face of the ice sheets tossed the flour into violent sandstorms. In places, great blocks of ice fell from the faces of retreating ice sheets. Blowing dirt built up around them, and when they melted, they left in place the kettle lakes of the prairie states an
d Washington and New York states. In other places, the blowing dirt — sand and flour that the glaciers ground from bedrock — covered vast areas of ice, insulating it. This ice, insulated beneath soil, stagnated. Grasses and later forests grew in the soil, with the stagnant ice beneath. Eventually, the stagnant ice melted, and the ground, deprived of the subterranean ice, subsided. What had been upland forests sank into lowlands, wetlands, and swampy depressions.

  One seed at a time, plants moved onto the quickly changing ground. Marsh marigold, mountain monkshood, and mountain harebell all moved south from Beringia. Plants with wind-borne seeds moved faster than those that hitched rides in the guts of animals. Hickories were among the slowest, taking two thousand years to journey up the Mississippi Valley and then east to Connecticut. Chestnuts, too, crawled along, averaging a mile or so every ten years. Hemlocks and maples were twice as fast. Certain oaks sprinted at more than two miles every ten years, neck and neck with eastern white pines.

  As the land changed and new plants arrived, the forests changed. Pines replaced spruces. Balsam firs, birches, elms, and oaks replaced pines. At certain places and certain times, forests changed during the course of a human lifetime.

  As the ice melted and the land rebounded, great rivers and their drainages changed, too. Arctic grayling, northern pike, and lake whitefish survived glaciation in the Yukon River and its tributaries, then migrated into the Mackenzie River. They did not migrate along coastal waters, but rather through a lake that formed as the glaciers melted, a lake that joined the two rivers, another open gate. Great Bear Lake, Great Slave Lake, and Lake Athabasca were at one time part of Lake McConnell, which drained for a time into the Mississippi River and for a time into the Mackenzie River and then into what would become Lake Superior, switching back and forth as floodgates of ice opened and closed. Certain fish evolved for a while behind the gates, then spread out when the gates were opened. The northern pike and burbot of Alaska hail from Beringia, but the northern pike and burbot of the lower states hail from waters south of the ice sheets. Genetically, they are not the same.

  Humans passed through the gates more than once. They came, it seems, as early as forty thousand years ago, but these early North Americans left little behind. What little they did leave was primitive and crude, nothing more than rocks with an edge, the kind of thing that one might pick up and skim across a lake without noticing that it had once been worked by human hands. The more recent Clovis people left stuff lying around, pretty stuff, symmetrically carved functional art. The first remnants of the Clovis people found in modern times were in New Mexico, but ongoing searches have turned up Clovis sites throughout the United States and down into Mexico and even Central America. At sites dated to thirteen thousand years ago, the Clovis people left spear tips and knives and scrapers made of chipped stone, bones marked by the signs of butchering, and rocks burned red. Most abundantly, they left stone flakes, fine chips of stone, the waste from working rocks into more useful tools. They ate more than 125 species of plants and animals, including mammoths. Although what they wore is unknown, it seems likely that they would have had the sense to wear skins in cold weather. Closer to the ice, with the wind ripping down from the ice sheets, it seems obvious that they would have worn one layer of fur turned in toward the body and another with the fur turned out.

  Around the time of the Clovis people, the mammoth disappeared. Other animals believed to be on the Clovis people’s menu also disappeared: North American camels, two kinds of deer, two kinds of pronghorn, a kind of llama, the stag moose, the shrub ox, the woodland musk ox, five species of the American horse, and mastodons. Giant beavers, as big as today’s black bears, disappeared. The American cheetah, the dire wolf, the saber-toothed tiger, the short-faced bear, and the American lion all disappeared. Smaller mammals — the sort some believe less likely to show up on a menu — survived. Certain scientists saw this as circumstantial evidence and blamed the Clovis people for the extinctions, but other scientists argued that there were more clues to consider. To anyone who has hunted an elephant or a musk ox or a moose with a stone spear, the starring role of man in these extinctions seems miscast. More likely, humans helped the extinctions along as the animals succumbed to a rapidly warming environment — roaring winds blowing from melting glaciers and sandstorms carrying megatons of glacial flour. They succumbed to a sudden change that likely made winters and summers even more uncertain than they had been during the Little Ice Age. It was a time when grasslands became forests, forests were buried in drifting sand, and massive lakes drained overnight — a lake one day, a mud bed the next — through white-water torrents bigger than today’s Mississippi River. Tallgrass prairies became shortgrass prairies. The Arctic steppe of Beringia became overgrown with shrubs and then trees before disappearing altogether under the rising Bering Sea. Disease, too, may have played a role in these extinctions. But this much is certain: the big mammals were there, south of the ice, and they were in Beringia, north of the ice, and when the ice melted, many of them disappeared.

  Within a few hundred years of the extinctions, on the other side of the world, the Sumerians were busily inventing agriculture. But in North America, the hunt went on. Bison were still abundant, and various deer, and the delicately sized and flavored modern beaver. Grizzly bears kept the hunt exciting. Clovis boys sat around campfires and, with the timeless cockiness of teenagers, mocked the stories of ice sheets and mammoths and mastodons, and of a great-uncle who had been eaten by a saber-toothed tiger. The boys focused on their own prowess at hunting buffalo and on near misses with grizzlies. But occasionally they stumbled upon bones, upon tusks and teeth of mammoths and mastodons, and they may have wandered through boulder-strewn forests and grasslands, perhaps even having their own word for erratics, wondering why such large rocks would be resting so far from anything resembling a mountain.

  It is May sixth and warm in Anchorage, truly spring. To celebrate, I take my caterpillars Fram and Bedford from the freezer. They have been on ice since September twenty-third. I put the frozen but presumably undead bodies of my two patients in a mason jar lined with the budding leaves of birch and willow and sambucus. Optimistically, I poke airholes in the jar’s lid. I also take out my frozen mud, collected in September and stored in the freezer ever since. I open the jar to let the mud thaw.

  The Anchorage paper runs a full-page article on mosquito evolution. For the past five years, a pair of scientists have created the climate of New Jersey in an Oregon laboratory. The climate chambers have been stocked with mosquitoes from Maine. From the perspective of scientific inquiry, storing Maine mosquitoes in Oregon climate chambers that mimic New Jersey conditions is business as usual. The way things are going, Maine’s climate will be New Jersey’s climate in the foreseeable future. The mosquitoes have already shaved two weeks off their hibernation time. “In a woodsy bog on the road between Millinocket and Baxter State Park,” the paper says, “a mosquito that can barely fly is emerging as one of climate change’s early winners.” The mosquito may have had a trick or two to show the mammoth, North American camel, llama, deer, prong-horn, stag moose, shrub ox, woodland musk ox, American horses, and mastodons.

  Mammoths occasionally materialize out of thawing soil where rivers cut into banks of permafrost or where miners dig into icy gravel. Their tusks stand out, or blackened femurs as big as fence posts, or skulls with a large central aperture for the trunk. The skulls at different times have been mistaken for the skulls of unicorns and Cyclopes. In the past few centuries, more than fifty thousand tusks have been exported from the Taymyr Peninsula in Russia. Today Alaskans market mammoth tusks as expensive souvenirs.

  In 1977, a Russian miner working near the Dima River found a frozen carcass — not a skeleton, but a frozen carcass, covered with hair, frozen eyes intact and staring. In his excitement, he reportedly called out, “Mamonyonok!” — “Baby mammoth!” Frozen mammoths tend to be named. This one was named Dima, after the river. Before the miners could attract the attention of officials
, Dima’s carcass thawed enough to stink. Nevertheless, Dima’s heart and foot-long penis are displayed today in the St. Petersburg Zoological Museum.

  Dima was neither the first nor the last. Chinese writings from the second century b.c. describe thawing mammoth remains, saying they were “found beneath the ice, in the midst of the ground.” The Chinese text talks of flesh weighing a thousand pounds that “may be used as dried meat for food.” It indicates that rats flocked to a thawing carcass: “Wherever its hair may be found, rats are sure to flock together.”

  In 1901, the Russian Imperial Academy of Science heard of a carcass frozen in a cliff on the Berezovka River, above the Arctic Circle. Scientists traveled by Siberian Express, wagons, boats, and horse-drawn sleds to reach the site. By the time they arrived, wolves and foxes had devoured part of the mammoth. Local people had taken the tusks. Eugene Pfizenmayer, one of the scientists, wrote:

  Some time before the mammoth body came in view I smelt its anything but pleasant odor — like the smell of a badly kept stable heavily blended with that of offal. Then, round a bend in the path, the towering skull appeared, and we stood at the grave of the diluvial monster. The body and limbs still stuck partially in the masses of earth along with which the corpse had been precipitated in a big fall from the bank of ice.

  The scientists built a shelter over the mammoth and went about dismembering what was left of it. They learned that it had four toes and a flap of skin protecting its anus from the cold. They preserved its flesh with alum and salt, then shipped the whole thing to St. Petersburg. One of them wrote, “A thorough washing failed to remove the horrible smell from our hands.” The trip back to St. Petersburg, via sled at temperatures as low as sixty-seven below, began on October 15, 1901, and ended on February 18, 1902. Summed up, the expedition north, the butchering of the frozen mammoth, and the trip home took 291 days. Tsar Nicholas and Empress Alexandra viewed the carcass in St. Petersburg. The empress held a handkerchief to her nose. “Is there something else interesting to show me in this museum,” she said, “as far away from this as possible?”