and cooling, this part of Alaska should have been cooling. “Glaciers should be advancing,” Berg said, as he paused to wipe his brow with a bandana. “Climate change may be overriding the natural order of things.”
Then it was back into the canoe and only a short paddle to the south end of the lake, where we clambered out and approached a small berm with a hole dug into it and a pile of sandy soil to one side. This was it—our ice-shoved rampart, among the carpet of dwarf dogwood flowers and the dead leaves of the last year.
The men went back to work with a shovel, enlarging the hole they’d begun two days before on the landward side of the berm and from which they’d taken away a bit of woody evidence. Berg dug, and Reger squeezed and tasted soil samples, and then Reger dug and Berg talked to me about what they were doing. He spoke in his slow and always precise manner, in sentences that unfolded complete and orderly thoughts.
“What we’re doing here at Middle Finger Lake is excavating a berm that’s about two feet high, parallel to the shore, and it’s back thirty or forty feet from the shore. The base of the berm is about eight and a half feet above the present surface of the lake. These berms are formed by the ice bulldozing the lake sediments. This happens in the spring when the lake ice is breaking up and getting blown around by the wind. We find them on the south and southwest sides. The remarkable thing about these is that they’re so far above the present lake level—on other lakes we’ve found them twenty or twenty-five feet above the modern shorelines. Sometime in the past, the lake levels were very high—much higher than in the historic period. So we’re excavating this berm—or ice-shoved rampart—in hope of finding some pieces of wood we can date with radiocarbon. That will give us an idea about when these berms were formed.”
That—knowing when the lake levels were so high, the ice thick, and the northeast winds strong—could be matched to other climate data from that time period to tie regional effects to global ones and suggest linkages among conditions. An ability to “backcast,” as Sue Mauger was doing with stream temperatures on a shorter time scale, could help with forecasting a climate future.
On their previous outing, Berg and Reger had collected two small pieces of wood that, from their placement between bulldozed lake material and forest floor, appeared to have been at the bottom of two different rampart-building “shoving events.” Today, the goal was to get to a layer of soil underlying the whole berm. If they could find something woody there, they might get a maximum date—an upper limit on how old the berm might be.
Slate-colored juncos rustled through the underbrush, sparrows chattered, Reger paused to pinch some soil and what might have been part of a disintegrating root. He and Berg debated the theory they were working with—that the ramparts were created during the Younger Dryas period, some twelve thousand years ago. Younger Dryas was considered to be “a cold snap” after a warming period following the last big ice age, but there was some evidence from lake sediments and peat cores that it had been a wet period here on the Kenai.
That was the theory, but the first three radiocarbon dates they’d gotten from ramparts had dated from just fifteen hundred to five thousand years ago.
The two men argued the theory back and forth—whether the samples were good or might have been from deep roots, what the soil profiles told them, what it might mean if the ramparts were younger than they thought. Reger was leaning now to a mid-Holocene age. “That tells us a story, too.”
“A stranger story,” Berg said.
“It’s not that we’re arguing,” Reger said to me. “It’s just on the table.”
Reger was standing in a pretty big hole now. “Look what I see down here—a thin possible silt layer.” He and Berg studied the dirt, talked excitedly in technical terms, showed me—I could kind of see it—where the rampart ended and layers of overridden forest floor began. In another minute Reger was scraping, like an archaeologist, around a chunk of wood, and then a second one. Berg drew in his field notebook—the hole, the dimensions, notes on soil colors. He drew pictures of the little chunks of wood and then carefully wrapped them in aluminum foil.
Months later, when the radiocarbon dating was completed on those chunks of wood and twelve others from the ramparts at six different refuge lakes, the “stranger story” would be told. All the samples dated within the last fifty-two hundred years, in that recent interglacial period we know as the Holocene, when climate was thought to be reasonably stable. Why would there have been such high water at that time? What might have been going on with the climate then, here in this part of Alaska and globally? Were there other data sets that could support such a finding? Lake sediment studies in the refuge have suggested that the land in question had generally cooled and become wetter over the last nine thousand years, but there was, until now, no record of such extreme wetness.
Berg’s new theory posits that the ice-shoved ramparts associate with a large regional climate trend, perhaps involving “a series of stormy, high-precipitation anomalies that have occurred over the last 5,200 years, reflecting major changes in the North Pacific weather system.”7
We ate our sandwiches, and I wandered through the woods for a while, on animal trails that followed two smaller (and presumably more recent) ramparts that lay between the one we’d dug into and the shoreline. Had I come across any of these berms in the woods on my own, I would have guessed them to be glacial moraines or eskers, features I was more familiar with. In among the birch and the sweet-smelling balsam poplar stood a few blackened tree stumps, from the fire forty years earlier. Open areas around them were filled with bursts of purple fireweed.
I took a turn filling in the hole and then swatted more mosquitoes and listened to the far-off wavering call of a loon while Reger filled his plastic sandwich bag with lake plants to take home to his snail aquarium.
We boated back along the east side of the lake, watching for the indentation where we would portage to the next lake and then find a trail to the road.
I thought about the process of science—its posing of questions, all the tedious data collecting, the accumulation over time of observation, test results, reviews of results. The scientific process was slow and incremental, and conservative; it didn’t respond well to crises.
I tried to think as a geologist might, back through time and the processes that work on landscapes. Imagine a woody plant on a forest floor, twelve thousand years ago. Or five thousand years ago. What kind of a world did either date define? Twelve thousand years ago humans were just coming across, or along the coastline of, the Bering Land Bridge, land exposed because so much water was tied up in ice caps and glaciers. Five thousand years ago our ancestors were primarily hunters and gatherers, although, at least in Asia, farming was developing on a largish scale; some clever beings invented both the wheel and systems of writing. In both those time periods the amount of carbon dioxide in the atmosphere (measured from Antarctic ice cores) was around 250-280 parts per million. Today atmospheric CO2 exceeds 392 parts per million and is continuing to rise; levels of it and other greenhouse gases are higher than they’ve been at any time in at least eight hundred thousand years, which is as far back as ice core records go. Never in those eight hundred thousand years years did CO2 levels increase at a rate anywhere near what we’re experiencing today. Eight hundred thousand years ago Homo sapiens was still five hundred thousand years years away from evolving; our species has never had to cope with what are, indeed, unprecedented conditions—that is, unprecedented in our human history.
From his position in the stern, Berg talked about the Aleutian Low—that low-pressure center south of the Aleutian Islands in winter, characterized by high winds—that plays a major role in atmospheric circulation. If he and others could learn when the Kenai was particularly wet, climate modelers might be able to link that to other conditions at the time—for example the intensity of that Aleutian
