Climate change causes new rivers to form in the Arctic
Within decades, the strong warming of the Arctic leads to the formation of polygon patterns in the Arctic permafrost and to the formation of new rivers – a recipe for faster permafrost thaw.
The permafrost landscape in the Arctic is changing much faster due to climate change than previously assumed. Within just 60 years, the structure of a river network that intersects the permafrost landscape on Axel Heiberg Island in the Canadian High Arctic has changed fundamentally.
An international research team documented the interplay between climate change, freeze-thaw dynamics of the polygonal soil, and surface water inputs from flooding and snow and ice melt. While the sources of surface water in permafrost landscapes are generally known, the researchers said there was still a lack of understanding of how these determine the timing and rate of stream formation and the development of river networks.
Their research gave them a new perspective on the physical factors that determine the speed and pattern of river channel development in these fragile landscapes.
“One of the key processes we identified in the evolution of stream networks is that their development is influenced by the way water flows through fields of roughly 10-metre-wide polygons, created through the freezing and thawing of the soil in Arctic regions,” Shawn Chartrand, assistant professor in the School of Environmental Science at Simon Fraser University in British Columbia, Canada, and lead author of the study, said in a university news release. In addition, the timing, extent, and duration of flooding events play a role, as well as whether the underlying sediment particles are frozen or partially frozen.
During fieldwork, researchers focused on the Muskox Valley on Axel Heiberg. After their 2019 observations, which included LiDAR data, they searched for historical records from the region. They found aerial photographs from 1959 and compared them with their own observations to understand how the island’s landscape has evolved over a 60-year period.
“Interconnected physical processes can deepen river channels and expand river networks, creating more surface area for heat exchange, which can increase local rates of permafrost thaw,” explains Mark Jellinek, professor of Earth, Ocean, and Atmospheric Sciences at the University of British Columbia and co-author of the study. “These cascading effects can enhance the release of greenhouse gases in the Arctic as organic soil carbon thaws and the permafrost retreats.”
A digital elevation model (DEM) that the researchers created from LiDAR data of a 400-meter section of the valley allowed them to model water movement across the landscape. They found that floodwaters flowing through interconnected polygon valleys increased the likelihood of erosion and channel formation, Chartrand said.
When the valley lake floods and due to seasonal melting of snow and ground ice, water is added and collects downstream. The water enables the transport of coarse-grained sediments and the formation of channel systems along the valley floor. However, the timing of flooding during the thaw can affect how severe the erosion is.
“Warming air temperatures play a role here,” Chartrand explains. “We predict that erosion and sediment transport is sensitive to whether floods occur before or after a period of elevated air temperatures, because this influences the depth to which sediment particle substrates are thawed, and thus effects whether the particles are transported by flood waters.”
The researchers emphasize the urgent need to use such observational data to develop predictive physical models. These would help to better understand how Arctic river networks will evolve in the coming decades as warming continues and climate variability increases.
In addition to the increased release of carbon dioxide and methane from the faster-thawing permafrost, the transport of greater amounts of sediments, nutrients, and metals through expanding river networks in sensitive watersheds and fisheries could have potentially significant consequences for wildlife, aquatic life, and coastal populations.
Julia Hager, PolarJournal
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