To Brendan Kelly, who has spent 25 springs there, the ice covering the Arctic Ocean looks like a lunar landscape. But it isn’t really that lifeless. Detecting life in the snow and ice, he says, just requires the right sensory technology. And a leash.
Kelly’s detection systems have four legs and an exuberant urge to lollop off exploring the snow. They are trained Labrador retrievers, who can pick up the scent of ringed seals from 4 kilometers away.
Seal-sniffing dogs track the odor to drifts where female ringed seals have excavated snow caves for giving birth to pups. No traces give away the location from above because the seals enter through the ice below. “Only with the use of that nose on the Labradors can we go out and find out that that barren-looking icescape is in fact loaded with mammals,” says Kelly of the University of Alaska Southeast in Juneau.
“Loaded” reflects a certain perspective, of course, but those millions of square kilometers of frozen seawater atop the Arctic Ocean are no wasteland. “There is an elaborate ecosystem there,” Kelly says.
Yet just one resident of the ice, the polar bear, gets the giant share of attention in warmer parts of the world. In December 2006, the U.S. Department of the Interior announced that Arctic sea ice was melting so dramatically that polar bears would be evaluated for protection under the Endangered Species Act. The department’s decision on that listing is due in January.
So far, only the polar bears get a chance at threatened status, even though walrus, some of the seals and seabirds, and unknown numbers of smaller ice-loving creatures depend on that shrinking polar cap. It can be a restaurant or a refuge, and for the smallest citizens of sea ice, it’s the whole world.
The Department of the Interior may not know enough about these populations to make a bulletproof justification for listing them as threatened species. But Arctic biologists predict that receding Arctic ice will change the lives of the unlistables too.
Kelly thanks the bears for finally calling attention to what he calls “the severity of the climate-related changes visible in the Arctic.” Yet, he says, “we won’t do even that species much good if we don’t understand that it’s an entire ecosystem that’s imperiled here.”
Meltdown
Just to clarify a basic point: The current furor about the melting Arctic ice cover in coming decades refers to the Arctic in summer. During the winter months, for the next century and probably much longer, climatologists predict that the seawater in the Arctic Ocean will still freeze over.
At its peak, the winter Arctic ice spreads to cover nearly 15 million square kilometers. Come spring and summer, a quarter of it melts again. This year the annual meltdown set a new record for the skimpiest ice minimum in recent decades: A daily average of 4.28 million square kilometers of ocean remaining significantly ice covered during September, according to the U.S. National Snow and Ice Data Center in Boulder, Colo. This year’s ice shrinking was 23 percent greater than the previous extreme of Sept. 2005. The records show that the retreat has been growing more dramatic since surveillance began in 1979.
In September, the U.S. Geological Survey predicted that summer ice could melt quickly enough to wipe out two-thirds of the world’s current population of 20,000 to 25,000 polar bears by the middle of this century. And that’s with computer models for climate change that the USGS researchers call conservative.
The ice-retreat scenario hasn’t inspired any petitions under the Endangered Species Act except the one for bears, say Rosa Meehan of the U.S. Fish and Wildlife Service in Anchorage and Kaya Brix of the National Marine Fisheries Service in Juneau. “There’s a lot more information about polar bears,” says Meehan.
Movable feast
There’s a lot less information about walrus, even though lounging herds are conspicuous features of the ice. “I think of walrus as an ice-edge species,” Meehan says.
The Pacific subspecies spends the winter along the advancing margin of the sea ice as it freezes and expands to the south. That edge puts the attending herds tidily over the broad continental shelf west of Alaska, with plentiful clams and other seafood just an easy walrus-plunge down. As the ice front advances, it gradually edges the walrus across the feeding ground. “They’re moving down a banquet table,” says Meehan.
In spring and summer, the ice edge recedes. Males often retire to land and swim to nearshore seafood feasts. Females with calves generally ride the retreating edge north. Mothers leave their youngsters on the ice during forays for food.
This summer, that pattern changed. “Walrus have been coming ashore in northwest Alaska in the thousands, and that’s something that hasn’t happened in living memory in those numbers,” says Martin Robards of the University of Alaska in Fairbanks.
The females’ icy diving platform may have retreated too far north, he says. As the edge melts back into the polar basin, it moves over deep water, sometimes 2,000 meters, far beyond the walrus range of about 100 m. Hungry foragers have to swim back to the shallower shelf.
The lengthening commute may have forced the females to move back to land for a resting place between feeding trips, says Robards. Whether the young walrus managed to swim along, too, isn’t clear yet, but it’s easy to find females hauling out along the coast in a crowd. “It’s a noisy and fairly smelly place,” he says. “You don’t see the ground—it’s a horde of life.”
This change of habitat use does not mean that ice melting will be OK for walrus. “Clearly they can hang out on land, but it’s not without cost,” says Meehan. They acquire new menaces, such as brown bears, and encounter more human hunters. Land also raises the risk of disturbances. A plane droning overhead or rocks rattling down a cliff can send walrus stampeding into the water. “There’ve been reports of stampedes on beaches where hundreds of walrus have died,” says Robards.
So both Robards and Meehan worry about whether living on land will whittle away the population. But that brings up the question, how many walrus are there now? No one has managed a convincing count. “That is one of the Holy Grails of marine biology,” says Robards.
Birds fish
Like the walrus, black guillemots use sea ice for raising young. Even though guillemots nest kilometers away from the melting edge, its fate can make or break their nesting season, says George Divoky of the University of Alaska in Fairbanks. The summer of 2007 gave him a great case study in what can go wrong.
He has been monitoring a guillemot colony for 32 years, wintering in Seattle but migrating to Cooper Island in the Arctic for bird-breeding season. He sets out nesting boxes there, and in recent years at least 100 pairs of black guillemots have shown up. Without the box attraction, he says, he’d have to risk his life, as guillemots typically nest on sheer cliffs. With gravity in his favor, though, Divoky doesn’t flinch from other perils. “More people die from gingivitis than from being eaten by polar bears,” he says. (He does take his Sonicare toothbrush with him.)
In typical years, female black guillemots lay two eggs. Both parents spend weeks flying out to sea again and again to catch fish for the chicks. Divoky keeps track of what kind of fish the parents bring home, and he weighs chicks every day. Mom and dad mostly bring home Arctic cod, which congregate along the retreating edge of the sea ice.
Except for a polar bear so upsetting his field assistant that she left early, 2007 started out like a good year, Divoky notes. Chicks were gaining 14 grams a day by Aug. 12. Then parental hunting went wrong.
One day he realized that no adult had brought home a fish for 5 hours. When parents came back, they brought suboptimal species, mostly sculpin. Only the hungriest chicks ate them. Sculpin don’t fit easily into a chick’s gape, and several youngsters choked to death. Instead of gaining weight, they lost a tenth of their weight every day. Many of the second-hatched chicks died.
Cooper Island doesn’t offer Internet access, but a colleague of Divoky’s managed to phone him to say that the ice was receding fast. By about Aug. 12, it had moved more than 40 km from the island. That’s what had gone wrong, Divoky realized. No ice edge within reasonable distance, no cod.
The year had started well, so he could narrow down the possible explanations. For the first time, Divoky had the melancholy success of demonstrating within the same year that this test case of a bird colony went from thriving to crashing when ice melted away.
Sealing acts
Ringed seals as well as seabirds eat the Arctic cod dodging under the ice. Certain seals—such as the ringed, bearded, spotted, and ribbon—spend so much time there that biologists refer to them as ice seals.
The ringed seals show the tightest relationship with sea ice, depending on it for a safe haven in winter. They have the toughest flippers of the ice group and claw holes to surface and grab a breath as the seawater freezes. Seals patrol these holes and keep them open even as the ice thickens to several meters.
As snow falls, the seals leave it intact as a breathe-through blanket hiding their breaks in the ice. Pregnant seals work their way out through these snow-covered holes and burrow sideways into snowdrifts, excavating caves that Kelly’s Labradors find. Here, buried in snow, the females give birth even though the nursery air temperatures linger below freezing.
In checking the birthing caves, Kelly once recognized a seal he’d found the year before in the same area. Then he started checking and identified more comeback seals. Females may be returning to about the same spot every year, even though ice there has melted and refrozen. “Their GPS is about as good as ours,” he says.
Seal pups spend their first weeks hidden in the snow cave, and, when all goes well, the youngsters have grown up enough to swim away before the snow melts. Climate change risks disrupting this timing, says Kelly. He has seen early-spring warmth and rains collapse the caves. Pups in prematurely melting lairs rarely survive, he says. Water soaks the pups’ coat of baby fluff and ruins its insulating power. Failing caves raise the chances that predators will pick off an unusually high proportion of pups. When caves sag, even small predators such as ravens can dig out a pup.
What impact changing climate will have on ringed seal numbers is hard to quantify. In terms of counting even the current population, “I don’t think we’ve gotten very far,” says Kelly.
If the seal population shrinks radically, polar bears could have a harder time finding food. They’re specialized for prowling around ice and hunting seals. The bears lurk at breathing holes until a seal dinner pokes its head up for air, and a bear nose can catch the scent of a ringed seal through the snow. Adaptations that make polar bears kings of the ice turn against them on land, and they overheat easily when chasing prey. Even the unusual polar bears that summer on shore in Canada virtually fast until winter brings them sea ice and an abundance of seals.
Underworld
The ice residents that weave the bottom of the food web, sustaining the cod and thereby all the cod eaters, live the most intimately with the ice.
Even sea ice that’s frozen solid isn’t really solid, says Christopher Krembs of the University of Washington in Seattle. The various salts in seawater lower its freezing point. As the temperature drops and ice crystals grow, some of the salts move into brine, which trickles through internal rivulets. Even at –20°C, says Krembs, sea ice is shot through with brine channels.
Despite the cold and the mad swings of brine chemistry, hundreds of species live in sea ice. Rolf Gradinger, of the University of Alaska in Fairbanks, says that some 400 species of small photosynthesizers survive on the light that sometimes filters through the ice. Ice-bound herbivores graze on the photosynthesizers, and predators stalk the grazers.
“To be a big predator in a very poor system, you have to access a lot of space,” says Krembs. “The more you can squeeze yourself through little cracks, the more successful you’re going to be,” he says. “The ultimate king in that system is the amoeba.”
Ice organisms adapt physiologically, too, and Krembs has pioneered in describing their secretions of the large molecules, or exopolymers. These substances make the immediate environment more livable. “It’s just our ignorance that we call it ‘microbial slime,'” says Krembs.
The underside of the ice hosts more life, even algae when light permits. One of the showiest, Melosira arctica, lives only around northern ice and can dangle feathery fronds longer than a human diver’s body.
Gradinger frets about small Arctic species he has found only on ice that has been around for years, not on first-year stuff. Organisms adapted to stable ice may not survive open water, so the final thaw of the Arctic might wipe them out, he says. No, he has never considered petitioning for listing them as threatened species. Would anyone, outside a few loyal fans, mourn the looming disappearance of the shrimplike amphipod Apherus glacialis? It grazes ice-bottom algae “like a cow crawls over a meadow,” says Gradinger.
If, that is, the cow walked upside down on the meadow overhead. Under water.
It’s a different world, all right. But it is a world. To human eyes, the high Arctic may look barren as the moon, but, says Gradinger, “I think we have a wrong perception of ice.”
