Michael Rawlins and Team Find That a Wisconsin-sized Chunk of Alaskan Permafrost is Thawing
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In a first-of-its-kind study, a team of researchers led by geoscientist Michael Rawlins—extension associate professor in the Department of Earth, Geographic, and Climate Sciences and the associate director of the Climate System Research Center at UMass Amherst—has shown in fine-grained detail what happens when Arctic permafrost thaws.
Focusing on a Wisconsin-sized area of Alaska’s North Slope containing hundreds of rivers and streams flowing into the Beaufort Sea, the team analyzed 44 years of model data at one-kilometer grid resolution, revealing how massively runoff is increasing, the increased loads of previously frozen carbon flowing through northern Alaska’s rivers, and how the thawing season has extended into late-summer and fall. The results, published recently in Global Biogeochemical Cycles, helps us better understand just how one of the fastest-warming parts of the world is rapidly changing.
It’s hard to overestimate just how important Arctic rivers are to the planetary ecosystem. They deliver 11% of the world’s river water to an ocean that contains just 1% of the world’s ocean volume, making the Arctic, one of the fastest-changing parts of the globe, incredibly sensitive to whatever is happening in the rivers and streams. While much of that river water, and all the stuff carried in it, come from melting snow, permafrost thaw also plays a key role.
“Permafrost” is a bit of a misnomer, because there is a part of the permafrost called the “active layer” which freezes and thaws again every year. The active layer has been deepening in recent decades due to the warming climate, and this change is causing proportionally more groundwater to be delivered into Arctic rivers.
The active layer also contains vast stores of frozen organic carbon. When the active layer deepens, more of this carbon, in the form of dissolved organic carbon (DOC), washes into the rivers and, ultimately, the ocean. The Arctic Ocean receives a disproportionate share of the DOC delivered from rivers to oceans worldwide, and some of this carbon—more than 275 million tons—gets released as planet-warming carbon dioxide every year, which can create a vicious warming feedback loop.
That’s for the Arctic as a whole. But what about individual rivers, even small streams themselves? How are they faring as the world warms?
“What makes this question so hard to answer is that direct observations are very sparse in northern Alaska,” says Rawlins. “There are nowhere near enough river sample measurements to quantify inputs to estuaries along the entire Alaskan North Slope.”
One way to get around the paucity of data is with a model—the more precise the better—and Rawlins has spent the last 25 years developing the Permafrost Water Balance Model, which estimates a wide range of data, including snow accumulation and melt, changes in the active layer, and much more to get the best possible estimate of what is happening out in the field. In 2021, Rawlins expanded the model to simulate DOC, and in 2024 he and his colleagues modeled 22.45 million square kilometers of Arctic land and found that, over the next 80 years, the region would see up to 25% more runoff, 30% more subsurface runoff and a progressively drier southern Arctic.
“We’ve typically run the model on 25-kilometer grid cells,” says Rawlins. “This new study is the first time anyone has captured such a wide area of the Arctic—about the size of Wisconsin—down to the kilometer scale, and over such a long period of time: our model simulates daily river flows and coastal exports over 44 years from 1980 to 2023.”
It takes the supercomputer at the Massachusetts Green High Performance Computing Center ten continuous days to crunch all the data for each model run—and it’s worth it. “Our freshwater and DOC inputs to coastal estuaries will be useful to a broad range of stakeholders interested in these unique ecosystems in coastal northern Alaska,” says Rawlins, “including the Beaufort Lagoon Ecosystems project, which is helping to quantify exactly what’s coming through these coastal estuaries.”
The team discovered that, while thawing and runoff is increasing everywhere, the largest increases in DOC export are emanating from northwest Alaska. “It’s flatter over there,” says Rawlins, “which means there’s much more carbon from decaying matter in the permafrost that has been accumulating for tens of thousands of years. This is ancient carbon. The further east you go, the more mountainous it becomes. The soil is rockier and sandier, and so far less DOC is mobilized as the permafrost thaws.”
The most surprising result is how thawing of the permafrost is really what’s driving much of the change—and the permafrost thaw season has extended into September and even October, weeks longer than it has been in the recent past.
All of these changes are likely altering salinity, biogeochemical processes, and food web relationships in the coastal Beaufort Sea. Rawlins and his colleagues are now trying to understand how thawing of ice wedge polygons, which are ubiquitous across the high Arctic, is altering the flow of water and carbon to coastal zones.
“How much DOC finds its way to the ocean via rivers and streams is a part of the carbon cycle we don’t know much about,” says Rawlins. “We desperately need more of these land-to-ocean connection studies if we’re to fully grapple with the problem of global warming and the effects it will have on coastal ecosystems.”
This research was supported by the U.S. National Science Foundation and NASA.
Read more: Newsweek; Scientific American; ScienceDaily; Courthouse News Service; Talker News.
This story was originally published by the UMass News Office.