Climate change is transforming the rivers of the Arctic region.
The most dramatic shift is the rerouting of a major meltwater river in Canada that disappeared in what is, geologically speaking, the blink of an eye.
The meltwater from the Slims River, which existed for at least 300 years, disappeared in just four days.* Scientists called it a case of “river piracy.” After glacial melt rerouted the river, it shifted from flowing northward into the Bering Sea to flowing southward into the Pacific Ocean.
It’s one of a few major shifts occurring in the Arctic and sub-Arctic. Rivers in the Arctic are also losing ice almost a month early. That, too, is a rapid change, and one that has happened in just 15 years.
“It’s clear that warming temperatures are dramatically affecting what’s going on in the area,” said Tamlin Pavelsky, lead author of the study on river ice melt and a hydrologist at the University of North Carolina, Chapel Hill. His findings were published yesterday in Geophysical Research Letters, a journal of the American Geophysical Union.
The early disappearance of Arctic river ice is the first time that profound change has been observed, Pavelsky said. And while much of the research into the effects of global warming on the Arctic is centered on glacial melt and shrinking sea ice, the study shows that river icings are also dramatically changing.
Pavelsky said he got the idea for the study after a backcountry pilot flew him into northern Alaska for a canoe trip and said he had observed the change over 30 years of flying. The river ice is now retreating in mid-June, when it used to do so in mid-July. Scientists did not previously know that it was changing and had no idea it could occur so fast, he said.
Scientists also observed that the icings that don’t completely melt over the summer were smaller than ever observed.
The river icing, Pavelsky said, is an important part of the Arctic ecosystem, which has one of the wildest river systems in the world, since few humans live there. The icing happens when frozen Arctic rivers are bolstered by groundwater that freezes on top of it. The ice can grow to be more than 30 feet thick in some spots. The rivers support Arctic char and salmon populations and provide an essential water source for caribou, as well as a place for them to seek refuge from the clouds of mosquitoes that plague them in the summer months, he said.
Researchers used satellite data to examine 147 river icings between 2000 and 2015, and discovered that more than half, or 84, were disappearing earlier in the summer melting season or becoming smaller. None of the icings observed lasted longer.
Pavelsky said his latest findings are consistent with other profound changes to Arctic rivers that he has studied in the past. His previous work focused on rivers in Siberia that were flowing in winter months earlier than ever noticed before. The pace of the change is what is most alarming to scientists studying the area, he said.
“I am surprised at how rapidly it is happening,” he said of the ice melt. “The date it is disappearing is getting earlier by a day a year, which is really fast.”
‘A century’s worth of warming’
The pace of change to river flow in the Yukon region of northwestern Canada, part of the sub-Arctic, is a result of climate change, as well as the region’s unique geology, researchers found. The shift of the Kaskawulsh River—which came during the warm spring of 2016, when melting water carved a new canyon through the ice—in the sub-Arctic region was the first time scientists observed a river completely changing course in an extremely rapid timeline. Previous examples have been observed in the geologic record, starting when the last ice sheets of the Last Glacial Maximum period retreated.
The river piracy study was published on Monday in the journal Nature Geoscience. It was conducted by University of Washington geoscientist Dan Shugar and a team of researchers at six Canadian and American universities.
There is already a significant body of research detailing how the warming of the Arctic and sub-Arctic is transforming the region by melting permafrost, sea ice and glaciers. But the river piracy event is the first time scientists have measured transformation over the course of days instead of years or even decades.
Like Pavelsky, Shugar discovered the phenomenon almost by accident. Last year, he and some colleagues traveled to the Slims River area to study its flow, but discovered that there was no water. Instead, there was a dry riverbed and choking dust storms that blinded them as they walked along the area where water once had flowed, he said. Traveling by helicopter, they eventually tracked the cause of the change to the headwaters of the river and noticed that melting of the glacier that fed it had rerouted the water and essentially shut off the Slims River.
“The river essentially shut off in four days, but it was caused by a century’s worth of warming,” Shugar said.
That, in turn, drained the level of Kluane Lake, which is the largest body of water in the Yukon. The river piracy event fed the Alsek River and shifted a profusion of fresh water into the Gulf of Alaska.
Drastic rerouting of rivers has been observed in the Andes, the Himalayas, Iceland and other places across the globe, but only in the geologic record, or many decades ago, Shugar said.
And while he doesn’t expect to routinely see rivers rerouted as a result of climate change, it’s a sign that more can be expected as the rapid warming transforms areas now covered by ice. It’s a reminder that climate change is already happening now and transforming an increasingly larger portion of the planet than scientists once expected to find, he said.
“Climate change is occurring, and it’s occurring here, not just on the other side of the world, and with it are likely to be some surprises that we haven’t anticipated,” Shugar said.
That scientists have now documented the redirection of a river should alert researchers that such dramatic shifts in water sources could at some point affect population centers, wrote Rachel Headley, a geoscience professor and glacier expert at the University of Wisconsin, Parkside, in an essay accompanying the study. It is significant that researchers were able to track the shift almost in real time because glacial melt is a water source around the world, and a dramatic shift in one region could indicate that others are possible in the future.
“As the world warms and more glaciers melt, populations dependent upon glacial meltwater should pay special attention to these processes,” she wrote. “Additionally, the impacts should catch the attention of not only those who study rivers and climate change, but also of anyone interested in water, sediment and nutrient supplies.”
*This sentence was edited after posting. The original misidentified the Slims River as the related Kaskawulsh River.
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.
