2023-09-13 21:45:02
Natural polygons and channel networks on the west side of Axel Heiberg Island in the Canadian Arctic. (Shawn Chartrand/Simon Fraser University) A study recently published in the journal Nature Communications demonstrates that global warming in the Canadian High Arctic has profoundly modified the structure of a river network in just 60 years.
By documenting an interaction between climate change, soil freezing and thawing dynamics, and surface water input through flooding and melting snow and ice, researchers at Simon Fraser University and the University of British Columbia have developed a new view of the physical controls that govern the speed and pattern of river channel development in these fragile landscapes.
“One of the key processes we have identified in the evolution of stream networks is that their development is influenced by the way water flows through fields of polygons approximately 10 meters wide. large, created by freezing and thawing of the ground in Arctic regions,” explains Shawn Chartrand, professor at Simon Fraser University and lead author of the study
He says this influence also depends on the timing, magnitude and duration of flooding, as well as whether the underlying sediment particle substrates are frozen or partially frozen. “Interconnected physical processes can deepen river channels and expand river networks, creating a larger surface area for heat exchange, which can increase local permafrost thawing rates,” says Chartrand.
The researchers traveled to the uninhabited Axel Heiberg Island at the start of one of the most intense summer warming episodes on record. Their field research focused on the Muskox Valley, east of the Muller Ice Sheet.
A scientist collects topographic data using a mobile laser scanning system. (Shawn Chartrand/Simon Fraser University) “Cascading” effects
The study says scientists combined aerial photographs from 1959 with field observations to understand how the landscape of Axel Heiberg Island evolved over a 60-year period. “These cascading effects can increase greenhouse gas emissions in the Arctic as soil organic carbon thaws and permafrost retreats,” adds Mark Jellinek, co-author of the study and professor at the University of British Columbia.
Using data collected by cutting-edge technologies, experts produced a digital elevation model (DEM) of a 400-meter section of the valley. “Through modeling water movements in the landscape, we discovered that floodwaters channeled through interconnected polygons increase the likelihood of erosion and channel formation,” emphasizes Mr. Chartrand.
As such, the study reveals that valley lake flooding and seasonal melting of snowpack and ground ice bring water that pools downstream of the valley, creating the conditions necessary for transport of sediments and the development of channel networks along the valley floor. However, the timing of flooding during peak thaw can influence the extent of erosion.
According to Chartrand, warming air temperatures play a role in this, “We predict that erosion and sediment transport are sensitive to whether flooding occurs before or after a period of high atmospheric temperatures. . »
The future challenge, the researchers say, will be to apply these data to produce predictive physical models that will help understand how Arctic river networks will evolve over the coming decades, marked by both warming and intensification of climate variability.
“Action is all the more urgent as expanding river networks will transport greater sediment loads as well as nutrients and metals into fragile river basins and fisheries, with potentially significant consequences for wildlife, waters and coastal populations,” conclude the researchers.
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