Rivers Speeding Up Arctic Ice Melt at Alarming Rate, Experts Sayhttps://phys.org/news/2022-01-rivers-arctic-ice-alarming-experts.htmlFreshwater flowing into the Arctic Ocean from the continent is thought to exacerbate Arctic amplification, but the extent of its impact isn't fully understood. New research led by Panyushkina measures how the flow of the Yenisei River—the largest freshwater river that flows into the Arctic Ocean—has changed over the last few hundred years, and describes the impact freshwater has had on the Arctic.
Previous studies have attributed recent changes in wintertime freshwater flow into the Arctic to warming air temperature, seasonal precipitation changes or snowpack. But more recent research, including Panyushkina's study, suggests that the primary driver is actually degradation of permafrost—or frozen ground—as well as forest fires across southern Siberia.Panyushkina's research, funded by the National Science Foundation Polar Office, is published in the journal
Environmental Research Letters.... Annual stream flow information is commonly used by water managers to reveal the average changes in stream flow trends. But Panyushkina and her team did something novel when they decided to also investigate winter stream flow specifically.
"We found an unprecedented increase in the winter flow rate over the last 25 years," Panyushkina said.
This winter flow rate is nearly 80% above the average seen over approximately 100 years.
"In contrast, annual flow fluctuated normally during the 300-year period, with only a 7% increase over the last 25 years," Panyushkina said.
... The winter stream flow data revealed the role of permafrost melt on Arctic ice.
Since ice covers rivers during winter in Siberia, the team's stream flow measurements only captured information about river water that originated underground rather than from the sky. That includes water from thawing permafrost, as well as water from sub-permafrost aquifers, as permafrost loss leads to an increased exchange of water between the river and aquifers. These two sources of groundwater are warm compared to the frigid air above, and when they eventually flow into the Arctic Ocean, they melt the ice.
... Forest fires are also thought to be a driver of Arctic ice melt.
"We know the frequency and intensity of forest fires in Siberia have been increasing," Panyushkina said. "When fires happen in forests with permafrost, there is deep thawing under the fire event, and the affected area often doesn't recover for up to 60 years. When we have large-scale fires and long-burning fires and more frequent fires, we're maybe hitting the critical point when permafrost degradation cannot return to normal. Forest fires are also another process that increases connectivity between aquifers and stream flow."
The combined effects of permafrost degradation and fires are very strong at the Yenisei River basin, with more fresh water and heat flowing into the Arctic Ocean in recent decades, according to the study. In turn, melting sea ice also exacerbates global warming.
... "There are two more Siberian rivers similar in size to the Yenisei," she said. "If we can quantify the stream flow from those rivers, we'll have more precise and clear understanding of its impact on the Arctic."
Irina P Panyushkina et al,
Unprecedented acceleration of winter discharge of Upper Yenisei River inferred from tree rings,
Environmental Research Letters (2021)
https://iopscience.iop.org/article/10.1088/1748-9326/ac3e20
