The Arctic continues to bear the brunt of climate change’s current effects, with new research showing that Arctic river ice is accruing in smaller amounts and melting earlier in the season.
Arctic groundwater comes to the surface and freezes on top of already frozen rivers, and these deposits of ice grow throughout the season until whole river valleys are covered. Some river icings have grown to over 4 square miles, and as deep as 33 feet. Traditionally, they start melting in the middle of July, which keeps many rivers running long after they would otherwise have dried up, and provides fresh water for many different creatures and habitats.
But over the past 15 years, there has been less of that ice forming, and it’s been melting about a month earlier. This means habitats that rely on that water melting later are getting less water overall, as it melts too soon and there is less of it to melt in the first place.
Looking at 147 rivers icings in the U.S. and Canadian Arctic using satellite data, Pavlesky and Zarnetske discovered that 84 of those are becoming smaller or disappearing earlier in the season. The minimum area of ice also shrank a lot during the study period. In 2000, there were 30 square miles of ice, but there were only 2 square miles in 2010. The minimum ice area has rebounded a little bit: it was up to 3 square miles in 2015.
“This is the first clear evidence that this important component of Arctic river systems—which we didn’t know was changing—is changing and it’s changing rapidly,” said lead author Tamlin Pavelsky of the University of North Carolina Chapel Hill.
The exact mechanisms of how climate change is affecting these rivers is as yet unknown, it could be that higher temperatures are directly affecting the ice, or that it is more subtly impacting groundwater, and how that water interacts with rivers.
“While glaciers tell us about climate in the mountains and sea ice tells us about sea-atmosphere interactions, the processes that control river icing may offer great insight into how groundwater and surface waters are connected in the Arctic and how our headwaters will be connected to the ocean in the future,” said study co-author Jay Zarnetske of Michigan State University.
In the meantime, these rivers and their related ecosystems are going to continue to change as the world’s overall climate warms.