Natural polygons and channel networks on the western side of Axel Heiberg Island in the Canadian Arctic. (Shawn Chartrand/Simon Fraser University) A recent study published in the journal Nature Communications shows that global warming in the Canadian High Arctic has profoundly changed the structure of a river network in just 60 years.
By documenting an interaction between climate change, ground freeze-thaw dynamics, and surface water input from 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 rates and patterns river channel development in these fragile landscapes.
“One of the key processes we have identified in the development of river networks is that their development is influenced by the way water flows through polygon fields approximately 10 meters wide. Large fields created by freezing and thawing of 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, severity and duration of the flood, as well as whether the underlying sediment particle substrates are frozen or partially frozen. “Associated physical processes can deepen river channels and expand river networks, creating greater surface area for heat exchange, which can increase the local permafrost thaw rate,” says Chartrand.
The researchers traveled to the uninhabited Axel Heiberg Island at the start of one of the most intense summer warming episodes ever. Her fieldwork 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
According to the study, 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 may increase greenhouse gas emissions in the Arctic as soil organic carbon thaws and permafrost retreats,” adds Mark Jellinek, study co-author and professor at the University of British Columbia.
Using state-of-the-art technologies collected data, experts created a digital elevation model (DEM) of a 400-meter-long section of the valley. “By modeling water movements across the landscape, we found that floodwaters channeled through interconnected polygons increase the likelihood of erosion and channel formation,” emphasizes Mr. Chartrand.
Therefore, the study shows that flooding of valley lakes and seasonal melting of snowpack and ground ice cause water to accumulate downstream of the valley, creating the necessary conditions for the transport of sediments and the development of channel networks along the valley floor. However, the timing of flooding during the peak of the thaw can influence the extent of erosion.
According to Chartrand, warming air temperatures play a role: “We assume that erosion and sediment transport are sensitive to whether flooding occurs before or after a period of high atmospheric temperatures.” »
The future challenge, according to the researchers, will be to use this data to build predictive physical models that will help understand how Arctic river networks will evolve in the coming decades, driven by both warming and intensifying climate variability Marked are.
“Action is even more urgent as expanding river networks will transport greater loads of sediment, nutrients and metals into sensitive river basins and fisheries, with potentially significant consequences for wildlife, aquatic environments and coastal populations,” the researchers conclude.