A new study offers one of the clearest pictures yet of what happens as Arctic permafrost thaws. Led by geoscientist Michael Rawlins at the University of Massachusetts Amherst, the research provides detailed insight into how warming temperatures are reshaping water systems and releasing long-frozen carbon.
The team examined a region of Alaska’s North Slope roughly the size of Wisconsin, where hundreds of rivers and streams drain into the Beaufort Sea. Using 44 years of model data at a resolution of one kilometer, they found that runoff is rising sharply, rivers are carrying increasing amounts of carbon, and the thaw season is extending later into the year, now reaching late summer and fall. The findings were published in Global Biogeochemical Cycles.
Arctic Rivers Play an Outsized Role in the Global System
Rivers in the Arctic have a surprisingly large influence on the planet. They deliver about 11% of the world’s river water into an ocean that holds just 1% of global ocean volume. This makes the Arctic Ocean especially sensitive to changes occurring in rivers and streams across the region.
Although melting snow supplies much of this water, thawing permafrost is becoming increasingly important. The ground contains a layer known as the “active layer,” which freezes and thaws each year. As the climate warms, this layer is getting deeper, allowing more groundwater to flow into Arctic rivers.
Thawing Soil Is Releasing Ancient Carbon
The active layer holds large quantities of organic material that have been frozen for thousands of years. As it deepens, more of this material is released into rivers as dissolved organic carbon (DOC), eventually reaching the ocean.
The Arctic Ocean already receives a disproportionate share of this carbon compared to other parts of the world. Each year, more than 275 million tons of it are converted into carbon dioxide, adding to global warming and creating a feedback loop that can intensify climate change.
Limited Observations Make Modeling Essential
Understanding how individual rivers respond to warming is challenging because direct measurements in northern Alaska are limited.
“What makes this question so hard to answer is that direct observations are very sparse in northern Alaska,” says Rawlins, extension associate professor of Earth, Geographic, and Climate Sciences at UMass Amherst. “There are nowhere near enough river sample measurements to quantify inputs to estuaries along the entire Alaskan North Slope.”
To address this gap, Rawlins developed the Permafrost Water Balance Model over the past 25 years. This model estimates key processes such as snow accumulation, melt, and changes in the active layer to better represent real conditions. In 2021, it was expanded to simulate dissolved organic carbon, and in 2024 it was applied across 22.45 million square kilometers of Arctic land.
The model suggests that over the next 80 years, the Arctic could experience up to 25% more runoff, 30% more subsurface flow, and increasing dryness in southern areas.
High-Resolution Modeling Reveals New Patterns
Previous versions of the model used grid cells that were 25 kilometers wide. This study improves on that by capturing changes at a much finer scale.
“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.”
Running the model required substantial computing power. Each simulation took 10 continuous days on a supercomputer at the Massachusetts Green High Performance Computing Center.
“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.”
Northwest Alaska Shows the Biggest Carbon Increases
The researchers found that while runoff and thawing are increasing across the region, the largest rise in carbon export is occurring in 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.”
A Longer Thaw Season Is Driving Change
One of the most notable findings is how much of the change is tied directly to permafrost thaw. The thaw season now lasts longer than in the past, extending into September and even October.
These changes are likely affecting salinity, nutrient cycles, and food webs in the Beaufort Sea. Researchers are now studying how ice wedge polygons, a common Arctic landscape feature, influence how water and carbon move toward coastal areas.
A Critical Gap in Understanding the Carbon Cycle
“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.”
The research was supported by the U.S. National Science Foundation and NASA.
