When archaeologists examined the Amaknak Bridge site artifacts, they found the usual bones—harbor seals, sea lions, fur seals, otters, puffins, murres, cod, and salmon. But they also found more unexpected artifacts: abundant remains of bearded and ringed seals, including juvenile ringed seals.
The finds were surprising, since both species spend critical parts of their lives on sea ice; ringed seals, for instance, birth their pups on ice, hiding them in layers of snow to protect them from polar bears. But there’s no sea ice on this island today, or in historical memory, even in the dead of winter. In 2017, the Arctic sea ice crept only as far south as Alaska’s Bristol Bay, still about 350 miles north of Unalaska. That’s further than the distance from Montreal to Boston.
“I remember thinking, that’s crazy,” says West, recalling the first time she heard about the find. “But I know the person who was identifying the stuff, and I have great confidence in her work, and I thought, that must be a pretty remarkable place.”
So, what were these ice-loving seals doing in a place with no ice? Did they get lost? Did they drastically change their behavior? Did the Unangan hunters start traveling far north to harvest them? Or did the Neoglacial cooling period hit the Aleutians so hard that the harbor iced over? That would mark a dramatic change for the island’s inhabitants.
“It would be like Boston Harbor freezing over and polar bears appearing on our landscape,” says West. “That would be kind of shocking. We’d have to change the way we do things a little bit.”
The artifacts from the Amaknak Bridge and Margaret Bay sites, along with those from another nearby site, Amaknak Spit, now live at the Museum of the Aleutians in Unalaska. They are a remarkable scientific collection. The most valuable bounty comes from the site’s garbage piles, or middens, where thousands of shells of butter clams have leached calcium carbonate into the acidic soil, keeping bones and teeth remarkably well preserved, with plenty of shells left as well.
Working with a $650,000 grant from the National Science Foundation, West and her two co-PIs—Michael Etnier, an anthropology research associate at Western Washington University, and Fred Andrus, a professor of geology at the University of Alabama—plan to reexamine the animal bones, searching for more evidence of bearded and ringed seals, as well as evidence of other ice-loving mammals like polar bears and belugas. Her team will also chemically analyze both ancient and fresh clamshells, trying to pin down an estimate of ancient water temperature. The team hopes that these two lines of evidence, along with an examination of other bones and artifacts, will paint a more detailed picture of what happened here thousands of years ago.
Cracked teeth and flipper bones
Michael Etnier picks up a heavy-duty Ziploc bag and pours a pile of bones onto a yellow plastic tray. As West and her two students, Anna Goldfield (GRS’17,’17) and Carly Buta (CAS’17), look on intently, Etnier begins a rapid-fire identification: sea lion distal radius, fur seal scapula, sea lion fifth toe, cracked canine tooth. Etnier, a marine mammal expert, is overseeing the mammal bone identification, and his skill and speed are astonishing; to the untrained eye, it all looks like garbage.
The kinds of questions that we're able to ask about these bones right now weren't even dreamed of 20 years ago.
“It is garbage!” Etnier shouts gleefully, sorting a harbor seal flipper bone from a fur seal humerus. “Somebody ate this as a meal 3,000 years ago and tossed it in the heap.”
“I love the bones because I can pick one up and tell you, ‘Oh, that’s a Pacific cod,’ and I know someone here was eating Pacific cod for dinner one night,” says West. “And it sounds silly, but it feels powerful.”
Etnier picks up a graceful curve of bone studded with tiny teeth—a seal mandible. “To figure out if these ringed seals were on the ice edge 30 miles from here or were being brought in, we need a massive, massive sample—which is what makes the Amaknak Bridge site such an amazing resource,” he says. “It was a gigantic site; they saved everything; it’s all been really well documented. So we’ll have these gigantic samples and we can then dig deeper and deeper into some of these research questions.”
The Bering Sea provides a critical habitat for many marine mammal species—not just residents, like sea otters, but also migrants, like right whales and orcas. Because each plays a role in a complex ecosystem that reaches southward to the Pacific Ocean, understanding how these mammals may—or may not—adapt to climate change could have widespread implications. “In the Bering Sea and North Pacific Ocean, we have seen marine mammals responding to environmental changes both through their behavior and in the health of their populations,” says West. For instance, in the last five years, an unusual number of orcas have been plundering fishing lines in the Bering Sea, wreaking havoc on the halibut industry. As the mammals change, says West, “their critical relationship to the ecosystem—and to commercial interests—becomes increasingly clear.”
Etnier’s analysis may offer more clues about mammals’ ability to adapt and also about the extent of past climate change: if he finds bones that were cracked to remove fat and marrow, for instance, that might indicate that people were short of food, struggling with the cold weather. But despite the promise hidden in this pile of bones, Etnier says that they alone can’t answer the climate question. That requires shell chemistry, he says: “The humble clam.”
The humble clam
Fred Andrus is back on the Amaknak Spit, having found no butter clams the previous day. He carries a spade and does not look optimistic. “If I were betting,” he says, “I’d bet against me.”
Andrus walks to the waterline and sticks his spade in. He breaks through a layer of black rock and popweed, finds his way to gravelly sand, and digs in. About six or eight inches down, water begins to fill the hole. “Holler if you see something that looks like a clam!” he says.
What are the rhythms of life of each individual organism, and how does that impact the chemistry?
Andrus is an expert in sclerochronology—studying the growth of shells, corals, and other hard parts of soft creatures, to better understand the conditions in which they grow. Clams are like flight data recorders, Andrus likes to say; “the trouble is, they’re not in a language we can understand.”
West, Goldfield, and Buta had spent days at the museum lab sorting through hundreds of ancient clamshells, selecting specimens for Andrus to analyze. (“It felt like a hundred billion clams,” says Goldfield, with a laugh.) Butter clams, which live up to 20 years, build their shells from calcium carbonate at regular intervals, resulting in growth lines that are analogous to tree rings. “Clams are really sensitive to their environment,” says Andrus. “They make their skeleton pretty much directly out of the raw material in the water.” Because of this, the makeup of a clamshell holds data about water chemistry and temperature. Andrus plans to analyze ancient clams in the hope of finding the prehistoric water temperature—and, thus, evidence of sea ice.
But to analyze the old clams, he needs to create a model, with modern data. Andrus and his graduate student, Christine Bassett, with the help of Missy Good from the University of Alaska Fairbanks, had been collecting temperature readings and water samples in this section of the spit for a year, and now they need the final bit of data, samples from fresh clamshells. Bassett and Good had been diving in the frigid deep water and had found a few baby clams, but Andrus wanted more.
Standing over his waterlogged pit, Andrus saw a few tiny bubbles breaking the surface of the cloudy water. “Maybe?” he says. “Could just be a worm.” But within a minute, he reached in and pulled out a butter clam. He held the gritty clam, a grin spreading across his rain-splashed face. “Awesome,” he says. The clam spit a small burst of seawater.
The data Andrus develops could be useful well beyond this current project, he says. “We’re focusing on butter clams for the archaeologists, but yesterday we collected, like, five different species of shellfish,” he says. Blue mussels, he notes, are a common food source throughout the world. “The mussels have commercial value, and there are actually some significant questions about their shell chemistry, their growth, that’s valuable in itself.”
Regarding the Unalaska project, Andrus cautions that he won’t be able to create a “flawless digital thermometer of the past. We’re never going to be able to come up with a definitive sea surface temperature, but we’ll be able to say it’s cooler or warmer than usual,” he says. “If we use 10 different methods, and they all tell the same story, that’s a pretty compelling story.”
Lessons in resilience
The story of the Unangan people is embedded in the artifacts they left behind, many of which remain buried around the island. West, Goldfield, and Buta drove out to Summer Bay, an inlet of the Bering Sea, to have a look at a recent dig. The bay joins a freshwater lake and the salmon were running home—so many you could see them jumping from the water. The professor and her students walked across the beach to an eroded hillside, where West pointed her trowel at a thin line of black running horizontally across the brown dirt. It’s the earthen floor of a house, with charcoal, shell, and fish bones ground into it, packed down and densely compressed. “To actually stand here and look reminds you—it reminds me, at least—that these were real people,” she says. “I’m looking at other humans’ stuff, and not just doing lab work and counting bones and looking at chemistry.”
What would those resilient ancient people make of us modern folk? In the past few months, our cities have been scorched by wildfires, flattened by hurricanes, shattered by earthquakes. It’s not so easy for us to go back and rebuild, to sew our own clothes, live off the sea. But maybe we can learn some lessons from the Unangan people about the value of listening to the land, living close to it, and adapting.
“The people here were living in an environment that presented dramatic seasonal challenges,” says West. But they were “pretty flexible in the face of change.
“While it may be difficult to see how such a small society can teach us about adapting to climate change today, working at this scale reminds us to look at our own, local environment—how is it changing as the climate changes? What will we need to do to adapt to those changes or protect our own infrastructure and resources?” she adds. “Many past ecosystems and people—like the Unangan people—successfully adapted as their environments changed, so knowing how and why they did will be a critical lesson for us, too.”
Written by Barbara Moran
Video & Photography by Devin Hahn
Clamshells and Climate Change: What Seal Bones and Clamshells Teach Us About Past Climate was originally published on the Boston University website.