by Curt Stager
Polar bears split from their brown/grizzly relatives roughly 200,000 years ago, perhaps when an ice age marooned a group of ancestors in some glacier-rimmed pocket of the Arctic. The length of that lineage overlaps the dates of the Eemian interglacial, so they’ve endured at least one long-term warming before. When an Icelandic scientist recently discovered an Eemianage polar bear jaw bone in Svalbard, an article posted online by the World Climate Report quoted him as saying, “the polar bear has already survived one interglacial period. So maybe we don’t have to be quite so worried about them.”
Derocher dismisses such comments as misleading. “To me, all it really means is that enough sea ice persisted through the Eemian to support polar bears.” Although some evidence suggests that the last interglacial saw open-water summers at the North Pole, we still have too few sediment core records from the Arctic Ocean to confirm or refute the idea of a total melt-off, and Derocher’s hypothesis may well be correct. He continued: “During the last ice age, they lived as far south as Germany and southern Scandinavia, but when it warmed up again they abandoned those areas even though some ringed seals still persist in the Baltic today. The bears probably can’t hang on for long without the stable, extensive sea ice that their hunting behavior centers on.”
If Anthropocene warming eliminates spring and summer sea ice altogether, there will be no northern refuges left to escape into. These supreme maritime predators will have to adapt to hunting on land or perish. That, of course, could be difficult if your coat is white on hunting grounds that are the color of dirt and leaves, and the only edibles available, from the point of view of your seal-specific digestive system, are the nutritional equivalent of junk food.
Meanwhile, brown bears will be moving northward in response to warming and the advance of boreal forests over tundra. What will happen when the two closely related species meet again? One “polar-grizz” hybrid with a brown-spotted white coat and a grizzly-like shoulder hump has already been documented (that is, shot) in Canada’s Northwest Territory. Perhaps such half-breeds might become more common in the future. More likely, though, the polar refugees will be outcompeted by their omnivorous relatives who already feel more at home in terrestrial habitats.
To Derocher, the writing is on the wall. As the ice in western Hudson Bay melts back earlier in spring, it gives the bears less time at the annual seal feast. And the ringed seals are feeling the effects of warming, too. “As the sea ice thins and weakens, you don’t see as many pressure ridges forming. Instead, it just rafts up into rubble piles that don’t capture drifts, and the seals are beginning to use ice chambers that aren’t as well insulated as fluffy snow lairs are. Their escape holes can sometimes freeze over now, so the mothers have to break through them to get to their pups, and sometimes they might not even find the entrances.” This change in den architecture also affects the bears. Derocher has recently seen some of them try to scrabble and scratch through solid ice in pursuit of denning seals, usually with little success. “It’s a new hunting method that’s a lot different from punching down through soft snow, but it’s not so much a matter of innovation on their part,” he said. “It’s more like desperation.”
The less a polar bear eats, the less it weighs and the less energy it can dedicate to reproduction. “It all boils down to body condition,” says Derocher. “Females who weigh less than 190 kilos are far less likely to breed successfully. Mothers who weigh more than that but are still underweight produce fewer cubs, and those cubs are born smaller.” In a world where body fat not only sustains you but also insulates against frigid winds and waters, the trend toward skinnier moms and fewer, smaller cubs points in only one depressing direction.
The main problem with the white bears, then, is not that they’re all drowning, or even starving to death. They’re just not breeding enough. It is the species itself, not so much the individual animals, that is most in danger now, especially in the southern limits of the Arctic where the effects of warming are felt most strongly.
Finding the numbers to support that claim, however, is no easy task. Polar bears cluster into more than a dozen circumpolar populations, and the few scientists who census them under difficult field conditions put their total numbers between 20,000 and 25,000, with about two-thirds of the animals living in Canada and perhaps 3,000 hanging out in the Barents Sea region. Meanwhile, a blizzard of controversy rages over whether those numbers are rising or falling as the ice cap shrinks.
Reports of increasing numbers are probably accurate in some locales, but some may also stem from recent improvements in census methods that allow more individuals to be found, and also from certain parties with vested interests in promoting bear hunting or denying climate change. In fact, the regionally comprehensive data needed to confirm large-scale trends of any kind are still lacking. In western Hudson Bay, though, the data are in; the population declined from about 1,200 animals in 1987 to 935 in 2004. According to Derocher, nutritional effects on reproduction are the most likely culprits, and sea ice retreat is the most likely cause.
No such slimming has yet been found among the Svalbard bears on the other side of the pole, but that’s not surprising. The ice in the Barents Sea is more extensive than it is at warmer, lower latitudes, and those bears still spend most of their time offshore bothering the seals. Most of the other subpopulations are too sparsely studied for us to be sure how they’re doing.
And what of the future? Some polar bears are beginning to eat more bearded seals and harbor seals as the ringed types become harder to reach from shore; those alternative prey will probably become more abundant while the favored sea ice habitats of the ringed seals retreat poleward, and an increase in harbor seal populations is already occurring in Hudson Bay. Perhaps the predators will manage to hang on this way in the more remote corners of the north.
But Derocher worries when he considers the future, including his own. “I used to think that I might not live to see these changes,” he said. “Now I’m close to fifty years old and it looks like they’ll happen before my career is over. I try to be optimistic about it, but the thought of spending my last productive years helicoptering around to document the demise of the polar bears isn’t very appealing.”
He will avoid that fate only if a lot of “ifs” fall into place. If ringed seals alter their breeding behavior appropriately, and if changing marine communities provide them with enough food, and if bearded and harbor seals can be as nutritious and attractive to bears as ringed seals are, and if landlocked polar bears can avoid competition and interbreeding with brown bears by taking refuge in northern Greenland or Svalbard, and if expanding northern industries and human populations don’t harm the wildlife much … then, maybe, we’ll still have polar bears with us when the Arctic Ocean finally refreezes at some later date in the deep future. The recovery from a moderate emissions scenario drops us back near today’s temperatures in a few tens of thousands of years, and an extreme scenario does it in several hundred thousand. But that’s a long time and an awful lot of “ifs,” and it’s hard to justify putting polar bears and ringed seals anywhere but on the list of probable losers as the Anthropocene runs its course.
Sadly, they’re not alone on that list. Walruses are also in jeopardy as their nursery habitats melt away. Walrus moms leave their helpless young behind to wait on sea ice platforms as the adults grub around for bottom-dwelling clams and crabs with their bluff, bristly snouts. But as the ice margins retreat farther and farther offshore, the water beneath them grows ever deeper and diving takes more time and energy. Walruses are large and powerful, but they don’t have gills and they can’t swim indefinitely, so they have to pull out and rest between dives. When water depths exceed 650 feet (200 m) or so, it’s just too energy-consuming to continue, and the adults have to go elsewhere or starve. Apparently, they sometimes abandon their infants in the process.
Nobody knows how widespread this problem is yet, but one heartbreaking set of field observations got a lot of media coverage recently. In 200
4, a U.S. Coast Guard icebreaker encountered nine baby walruses swimming alone in deep, ice-free Canadian waters. Shipboard biologist Carin Ashjian told Science Daily: “We were on a station for twenty-four hours, and the calves would be swimming around us crying. We couldn’t rescue them.” Like other ocean-dependent mammals of the north, walruses will have to learn new ways of balancing the demands of foraging and child care if they’re to survive the loss of summer ice. “The young can’t forage for themselves,” Ashjian continued in her interview. “They don’t know how to eat.” Instead, they live on mother’s milk for up to two years. But not if Mother is nowhere to be found.
For many of us who only experience the Arctic indirectly through the media, such a focus on mammals dominates our ideas about what lives up there. But there’s a lot more going on beneath the ice than above it, and it’s as much at risk as the large charismatic creatures topside.
Brine pockets in the sea ice form a porous network of channels that algae and other microscopic life-forms thrive in. The translucent ice also transmits enough spring and summer sunlight to sprout rippling meadows of algal filaments on the frosty undersides of the floating roof. Native species of tiny, shrimplike copepods wander those inverted green, white, and blue vistas to graze on the hanging gardens. Further up the food chain, Arctic cod dart in and out of sheltering crannies in the ceiling. Native Arctic whales, the ivory-white belugas and unicorn-tusked narwhals, are also closely linked to floating ice. They lack the prominent dorsal fins of many open-water whales, and that makes it easier for them to heave broken floes aside when they need to breathe and chase fish around the underwater icescapes.
The wide, shallow continental shelves of the Arctic Ocean are also very much alive, and some of the world’s densest aggregations of bottom-dwelling creatures thrive on organic detritus that rains down from the upper waters. Slithery brittle stars can number in the hundreds per square yard, and prickly sea urchins, cold-tolerant clams, fat sea cucumbers, and wriggling polychaete worms support a wealth of predators, from fish to birds to mud-grubbing walruses.
These highly specialized communities are now disappearing along with the ice. Species from lower latitudes are moving into the warming, opening waters, a process that some biologists call the “Atlantification” of the Arctic, with harbor seals, harp seals, and Atlantic cod among the most numerous of the immigrants. Meanwhile, whale-hunting orcas are also invading the newly ice-free waters. Their high dorsal fins make it difficult to navigate overhead ice cover, but an increasingly navigable polar ocean is leaving belugas and narwhals more vulnerable to orca attack. The calves of bowhead whales also make tempting targets, and the adult bowheads also face increasing competition from minke whales that are moving in on their feeding grounds.
Less visible threats face the native northern whales, as well. As southern animals follow the retreating ice northward, their microbes come with them, and pilot whales and their smaller relatives carry distemper, brucellosis, and other diseases that circumpolar belugas and narwhals currently lack resistance to. Although diseases are unlikely to exterminate entire species, adding epidemics to the list of new environmental pressures isn’t a pleasant prospect. Canadian marine mammal expert Otto Grahl-Nielsen recently estimated that half of the Arctic’s belugas and narwhals could eventually perish from imported distemper alone.
To be among the winners in the new Anthropocene Arctic, it now helps to be a generalist open-water species rather than an under-ice specialist. Even the tiny copepods are responding. Indigenous species with place-based names like hyperboreus and glacialis are giving way to immigrants that don’t need the hanging gardens of ice algae. Open-water fish such as pollock and salmon are replacing species adapted to frozen habitats, and aggressive Atlantic cod are displacing or eating their smaller polar cousins. In the Canadian Arctic, thick-billed murres, which resemble miniature, fast-flying, northern versions of penguins, are beginning to feed their chicks with capelin, a small plankton-eating fish that prefers waters with little or no summer ice, rather than the slightly larger Arctic cod that dominated their diets until the mid-1990s. Scientists who study seabirds also expect North Atlantic puffins and common murres to follow their traditional capelin prey northward as well, and razorbills (which look a bit like murres) are beginning to colonize rocky islands in the Hudson Bay region.
Judging from the changes already under way, life in an ice-free Arctic Ocean will probably be a mixture of whatever survives the de-icing and what moves in from the Atlantic and Pacific. But unsheathing the waves under the Anthropocene sun will also be like switching the lights on in a fertile greenhouse. Neil Opdyke, a noted authority on oceans and climates at the University of Florida, is one of many experts who foresee a burst of planktonic marine life ahead. “It’s going to be a very different and very productive ecosystem,” he speculated with me recently over lunch in Gainesville. “Not only will you have the ice-free ocean, but the thawing of permafrost will flood rivers with soil nutrients that will eventually end up offshore.”
That combination of warmth, light, and nutrition will trigger population booms of floating microalgae, or phytoplankton, and longer growing seasons and reduced ice cover have already boosted Arctic phytoplankton abundances during the past decade. Many of the world’s most productive fisheries develop on just this sort of ecological sweet spot, where plentiful light and nutrients support immense amounts of microbial growth. Such sites include upwelling zones along the coasts of Peru and Namibia, as well as the storm-stirred Southern Ocean. Phytoplankton, in turn, feed shrimplike krill and copepods, which support vast schools of plankton-eating fish. Then come the predatory fish, the gulls and puffins, and the orcas and harbor seals.
While Arctic cod and belugas fade away, the ice-free pole may open a new, food-rich refuge for other species that now face overharvesting and pollution problems farther south. With so much biomass production going on, enterprising humans will surely try to cash in on the new source of marine protein as well, with an open sea to harvest it from and an increasingly habitable coastline to support the industry. An online article posted by the Euroarctic.com news service in 2006 reported that Russian companies are already building specialized trawlers to harvest anticipated bounties of fish from the polar ocean.
But we’re forgetting something that could trouble these waters even if the whole place could be designated a hands-off sanctuary. Carbon pollution not only warms the oceans, it acidifies them, and Arctic marine organisms will be among the first to feel the corrosive effects of those acids. Even in a moderate 1,000-Gton emissions scenario, the chalky aragonite shells of many organisms, from coccolithophores to clams, will soon begin to dissolve in acidified polar waters. The coming one-two punch of climatic and chemical shifts will produce biological “no-analog” situations unlike anything seen during the Eemian or early Holocene, the nature of which even the most capable marine biologists can only guess at.
What might life be like in an ice-free and acidified Arctic Ocean? Total algal productivity probably won’t suffer much; most marine phytoplankton don’t build soluble carbonate coverings. The favored microalgal forms will probably be golden brown diatoms, whose sparkling transparent shells are made of acid-resistant silica rather than carbonates. Diatoms already thrive in the northern Atlantic and Pacific, and they’ll probably do well in the ice-free Arctic, too.
Among the invertebrates, potential losers might include shell-bearing pteropods, forams, mollusks, barnacles, urchins, crabs, and cold-water corals. Winners could include soft-bodied sea angel pteropods, jellyfish, anemones, sea cucumbers, and worms. Whether an ecosystem dominated by soft-bodied winners rather than crunchy losers is good or bad is a matter of personal taste, and it’s therefore judged differently in different situations. We might grimace at the thought of swarming schools of jellyfish at the North Pole, but such swarms are an awe-inspiring tourist attraction in the Pacific island nation of Palau.
In fact, nobody knows for certain which species will persist or perish
in that unfamiliar new world. The rich genetic complexity of life provides abundant material for natural selection to act upon and many marine organisms survived the acid bath caused by greenhouse gas buildups during the PETM superhothouse of the early Cenozoic. But we do know that major ecological changes are coming to the Arctic Ocean, not just in terms of climate but also of pollution, commercial development, and exploitation of natural resources, and that they will involve much more than polar bears alone.
The changes on land will be dramatic, too. Boreal forests are already spreading northward over former tundra, and tundra is creeping over formerly barren polar deserts. By some estimates, a large expansion of northern vegetation could partially offset some of the future greenhouse gas buildups by sequestering carbon in plant tissues. In certain regions, woodlands may meet the encroaching sea; in others, sodden bogs will hold the trees at bay. Native birch forests are expected to replace mossy tundra in much of Iceland, and pines are set to invade northern Sweden and Norway. Tundra flora in general are more likely to be harmed than helped by warming because they can’t move any farther north, though some may find refuge in colder Arctic highlands.
Along with the new plants, new animals such as moose, mink, red foxes, wood-boring beetles, and butterflies are also moving to higher latitudes. In Canadian rivers and lakes, southern brook trout and introduced brown and rainbow trout are likely to move north as well, perhaps displacing native char. Ironically, this means that the total biodiversity of the Arctic is increasing. It shouldn’t be surprising, considering the well-known pattern of higher species counts at warmer latitudes, and it might be thought of as beneficial were it not linked to the decline of unique species and were it not caused by human-generated pollution. However, little or nothing in terms of net global-scale biodiversity is gained by the change because the lengthening list of Arctic residents contains no organisms that are new to the planet as a whole. Most of the immigrant “winners” that are moving into the increasingly enriched communities of the warming Arctic are already well established farther south, but many of the “losers” have nowhere else to go and may be lost to extinction.