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Clams' Climate Secrets Prove Elusive in the Arctic

Field Notes
By Randall Hyman
Sep 5, 2014 12:07 AMNov 19, 2019 8:56 PM


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This is the third is a series of three posts from researchers’ expedition to northern Norway. Read others in the series here.

As fieldwork drew to a close last week off the northern tip of Norway, stormy seas flattened to a silvery smoothness and hungry fulmars swam about our fishing boat waiting for juicy leftovers. All we had to offer, though, were dead shells. The team of scientists I accompanied had still not achieved one of its prize goals: the discovery of live, deep-water clams of a very special kind. The confidence we brought at the beginning of the week was wearing thin. Dead shells dredged from 600-foot depths proved our prey were tantalizingly close, but elusive. For days we had successfully collected living samples in 50-foot waters, but the Arctica islandica clam, the oldest living multicellular animal in the world, is at the extreme reach of its range where the North Atlantic meets the Arctic. We needed live clams, and we needed them from the deepest possible waters at the edge of the continental shelf. Data gleaned from annual growth increments in shells at those depths reflect pure Gulf Stream waters (North Atlantic Current) where Atlantic current meets the Barents Sea, a critical intersection in the Arctic climate system. With this information the scientists on our team can reconstruct the triggers of ancient climate shifts and compare them to the present, as Arctic temperatures rise at twice the global average and sea ice dwindles to historic lows.

A Timeline of Shells

Al Wanamaker and Will Ambrose examine a dead shell dredged from continental shelf. Paleoclimatologist Al Wanamaker is a pioneer in this field, counting and cross-referencing clam shell increments and then measuring their isotopic content to pinpoint the environmental conditions present at any given point in his timeline. He takes into account various measurements. The amount of carbon-14 reflects when prevailing currents were in contact with the air. Arctic waters, locked under ice and submerged at great depths for centuries, contain less radiocarbon than Atlantic waters. From the oxygen isotopes Wanamaker infers water temperature fluctuations along his timeline. And it is the annual shell increments that reveal the clam’s exact age. When it’s all put together, Wanamaker knows what ocean currents dominated when, based on an animal that may have died hundreds of years ago or has managed to survive over half a millennium. “We can do lots with dead shells,” Wanamaker told me after the first frustrating day of dredging. “But we need living clams to give us a unique bar code that starts at the present. Then we can overlay that with older shells and work our way back.”

Watery Windfall

Al Wanamaker and undergrad Aubrey Foulk sort through piles of Arctica islandica on a stormy beach. The trip had brought an unexpected windfall of old shallow-water shells, actually – not just from dredging, but from the storms that stirred up the waters early in our trip. A few days previously we’d stumbled upon thousands of Arctica islandica shells at Sanden Bay, heaved ashore by overnight storms. “This is heaven!” Wanamaker exclaimed, kneeling on the white-sand beach and examining the goods. “This is unbelievable, seeing them in such heaps and piles. I’m trying to be so careful, but the waves will come in and just crush this stuff.” Assistants and scientists alike sifted through the piles and marveled at their good luck. “We can be very selective in what we bring back,” he had said, showing me one particularly heavy shell. “See how it’s thicker at the edge of the mantle? That’s an old one. But which one is the oldest? Pick one you like, it’s a lottery.” A clam that had a longer life means it’s a better yardstick to cross-reference, but a clam that’s older in how long ago it died is not what the team wanted from the continental shelf. Living, deep-water clams were the order of the day.

To the Shelf

On the second to final day of our fieldwork the group was like a football team going for State. We packed up our gear in the early morning, loading into two fishing boats as the scientists nervously exhorted one another with “To the shelf, to the shelf” and “We’re gonna get ’em.” Our boat headed for the far outer shelf while Wanamaker’s crew targeted a region closer, and we parted with a good-natured, “Let the games begin!” Sifting through our first scoops was frustrating. We spent most of an hour lowering, dragging and raising the dredge each time, with no live clams to be found. We wanted clams, but we also wanted to be the first to find them. Our skipper called the other boat on his cell phone, and announced that Wanamaker’s crew had snagged two live Arctica islandica.

Two ten-year-old Arctica islandica clams dredged living at 550-foot depth, farther north and deeper than any in history. The other team had scored first, but PhD student Maddie Mette, was smiling. “I am happy,” she said. “I was starting to believe they might not be there.” But the celebration was short-lived: we soon learned that the pair was just 10 years old, too young for cross-dating. “It was a toned-down Eureka moment,” Wanamaker told me back on shore. His crew had exchanged a few high-fives, but then eagerly dropped the next dredge, hoping for even older and more plentiful samples. But this was as good as it was going to get – neither that day nor the next were any more living clams retrieved from the deep waters.

Past in Future

Still, the researchers count the trip a success. “It’s actually a huge relief,” said Wanamaker, “No one’s ever found them this far north and this deep. But we’d like at least 50-year-olds to start cross-dating.”

Inside of Arctica islandica clam reveals muscular foot and mantle edge where new shell is accreted. They’re hopeful that they’ll find those elusive clams next year. In the meantime, Wanamaker has a few tricks up his sleeve. “By comparing the offset of the radiocarbon signal between shallow and deep-water shells that have the same overlapping 'bar codes,' we can figure when the deep-water ones were really alive,” he says. “We’re not skunked.” As Wanamaker knew before coming, Ingøya is a different game than Iceland, where deep-water clams are so bountiful that fishermen suction them from the ocean floor and use them as bait. The stakes are much higher here, but the potential rewards equally rich. On our last night the scientists sat around a dockside table in the chill of a late Arctic sunset planning for next summer, discussing new dredge designs, longer tow lines, and possibly renting a scallop-dredging boat rather than a fishing boat. With these fixes in place, they are confident they’ll find the many cousins and grandparents of those two ten-year-olds. And that once again they’ll pry open their climate secrets, past and present. All images by Randall Hyman

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