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The Mighty Taku Glacier Takes a Bow | Hakai Magazine

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In a world of shrinking glaciers, that yet another is melting hardly seems newsworthy. But the imminent retreat of the massive Taku Glacier near Juneau, Alaska, which until recently was still growing, is an exception. And while it does mark another unhappy milestone in the ongoing climate crisis, it also prompts thinking about how the glacier’s retreat will soon reshape the ecology of the Taku River valley. Paradoxical to its grim associations, the shrinking of the Taku Glacier will create new habitat for local wildlife, and bring fresh opportunities for recreation and science.

The Taku Glacier, called T’aaḵú Ḵwáan Sít’i in the Tlingit language, lies within the traditional homeland of the Taku River Tlingit First Nation. Winding 55 kilometers from the Juneau Icefield, the glacier forms a sprawling lobe beside the mouth of the Taku River, a biologically abundant waterway that cleaves its way to the Alaska coast from the mountains of British Columbia. Although the glacier has retreated in past centuries, it has been steadily advancing since the late 19th century.

This makes the Taku an outlier among North America’s coastal glaciers. As most of its counterparts shed ice throughout the 20th century, the Taku steadily added girth. Like an ice-age holdout, it buried a deep-water fjord and swelled up against steep mountainsides, obliterating ancient coastal rainforest. At its leading edge, it shoved sediment into a moraine nine kilometers across. The debris buried the glacier’s nose, and on its surface new plants and trees sprouted—even as the ice continued to push them toward the edge of the Taku River.

But that heyday appears to be over. Chris McNeil, a geophysicist with the US Geological Survey who first studied the Taku Glacier in 2009, reports that a freshwater moat has now formed along the glacier’s face, indicating that it is melting back from its moraine. McNeil attributes this initial retreat to climate change, which he says has raised local temperatures by 2 °C in recent decades.

However, other forces will soon be at work. As the Taku continues separating from its moraine, the moat will gradually expand into a lake 100 or more meters deep, McNeil says, which will be dammed from nearby ocean waters by the moraine. The lake water will exert a new erosional force on the ice that was once safely insulated by the moraine. Independent of the warming climate, it will speed the glacier’s decay. As time goes on, the shape and depth of the glacier’s basin may force additional erosion—a process tied more to physics than to climate.

Roman Motyka, a professor emeritus at the University of Alaska Fairbanks, who has studied Alaska’s glaciers for nearly 50 years, says melting could increase even more if the moraine, which rises just meters above sea level, erodes in places, either from the rush of meltwater or the powerful sweep of the Taku River. This would allow warmer salt water to reach into the lake, potentially triggering a runaway retreat like the one underway at Alaska’s Columbia Glacier, which has lost 20 kilometers of ice since the 1980s. Research by McNeil, Motyka, and others shows the earth beneath the Taku Glacier lies between 100 and 600 meters below sea level for a distance of 40 kilometers. As the glacier recedes and that mammoth trough fills with water, new beaches, hillsides, islands and, eventually, steep fjord walls will appear.

Like the scene following a wildfire, the landscape left behind by the ice will be colonized by a vibrant community of life. Alongside the water, lichens, fireweed, lupine, and young nitrogen-fixing alders will quickly build rudimentary soils and invite insects, birds, and small mammals, such as the minks and voles already present in the Taku River valley. Salmon and the wildlife they support will likely be other early arrivals.

Birds especially will seize on the new environment, which sits at the already-rich intersection of the Taku River and the Alaska coast. Some, including tundra swans, sandpipers, and sandhill cranes will stop to refuel along postglacial lagoons on their way to northern breeding grounds. Others, like plovers, terns, warblers, and kinglets will stick around to build nests, often not far from the ice.

Some sensitive species could also find new homes, including the Kittlitz’s murrelet, a compact seabird that tends to lay a single egg in a shallow scrape of gravel amid the sparse vegetation near tidewater glaciers. The Taku’s retreat could uncover new habitat for this and other species with specialized needs.

As the Taku begins discharging icebergs into its deepening lake, it may also provide new pupping habitat for harbor seals that congregate—sometimes by the thousands—to birth their pups on the ice of calving glaciers. The gatherings form a seasonal attraction for bald eagles, killer whales, and other species, which come to scavenge afterbirth or prey on seals. Near Alaska’s Bering Glacier, Bob Shuchman, a physicist at the Michigan Tech Research Institute, has observed hundreds of seals colonizing the icebergs where a moraine similar in ways to the Taku’s was breached by salt water as that glacier receded.

“It became a safe haven where seals could rest on icebergs away from their predators,” says Shuchman.

At the Bering Glacier, Shuchman led interdisciplinary research exploring how growth in plant and wildlife habitat, changes in water circulation, and more, represent system-wide shifts—the same kinds of shifts that may soon be playing out near the Taku.

The upwelling of life will also include new opportunities for human activities. Three historical Tlingit villages in the Taku’s vicinity attest to human uses stretching back through generations, including during past periods of glacial retreat. Historically, areas around calving glaciers have offered important resources, including gull eggs and seal meat, that are especially valued during the lean times before summer. The foods remain important today.

Motyka points to photos from the 1910s—before the glacier pushed its moraine alongside the Taku River—that show tour boats from Juneau visiting the glacier’s calving face. Today’s moraine would have to erode substantially to allow access by deep-draft vessels again, but kayakers and others will venture into the new landscape to glimpse what the Taku concealed.

Scientific opportunity will abound, too. McNeil says the Taku’s proximity to Juneau has helped establish a long observational record that will now inform study of its retreat. The record includes traditional Tlingit oral histories, which McNeil says have helped document the glacier’s past comings and goings.

Tlingit stories, for instance, describe times when the Taku Glacier advanced several kilometers beyond its current position and dammed the Taku River. The ice created an enormous lake stretching all the way to today’s Canadian border and separated Tlingit people living along the coast from those living inland. Stories recount people crossing the glacier for trade, and describe the scene when the river broke through the ice during periods of glacial retreat. The stories align with research by Motyka and others, who used tree rings, carbon dating, and riverside sediments to show that the Taku has both advanced and retreated during the last 3,000 years.

Evidence suggests fluctuations between the glacier’s advances and retreats often correlate with shifts in climate, although some changes do appear to occur independent of climate. Today, as the glacier makes a transition scientists tie to anthropogenic change, McNeil and others are eager to observe how the entire Taku system responds, from its sea level terminus to its high-mountain origins.

“We believe what will unfold with the Taku Glacier will ultimately give us more insight into tidewater glaciers locally and around the world,” says McNeil—insight that will further our understanding of how sea level rise, changes in meltwater circulation, and other processes with pressing global implications will play out in the decades to come.

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