A new study provides one of the clearest pictures yet of what happens when Arctic permafrost thaws. The study, led by geoscientist Michael Rollins of the University of Massachusetts Amherst, provides detailed insight into how rising temperatures are reshaping water systems and releasing long-frozen carbon.
The researchers studied an area of Alaska’s North Slope, roughly the size of Wisconsin, where hundreds of rivers and streams flow into the Beaufort Sea. Using 44 years of model data at a kilometer resolution, they found that runoff has increased sharply, rivers are transporting more carbon, and the snowmelt season has extended into the second half of the year, now reaching late summer and fall. The survey results are Global biogeochemical cycles.
Arctic rivers play a major role in the Earth system
Arctic rivers have an amazing impact on the planet. They pump about 11% of the world’s river water into the ocean, which has only 1% of the world’s ocean volume. This makes the Arctic Ocean particularly sensitive to changes occurring in rivers throughout the region.
Snowmelt provides much of this water, but thawing permafrost is becoming increasingly important. The ground has a layer called the “active layer,” which freezes and thaws repeatedly every year. As the climate warms, this layer deepens, allowing more groundwater to flow into Arctic rivers.
Ancient carbon is released as soil thaws
The active layer holds large amounts of organic material that has been frozen for thousands of years. As depth increases, more of this material is released into rivers as dissolved organic carbon (DOC) and ultimately reaches the ocean.
The Arctic Ocean already receives a disproportionate amount of carbon compared to other regions of the world. More than 275 million tonnes of that is converted into carbon dioxide each year, creating feedback loops that can accelerate global warming and intensify climate change.
Modeling is essential due to limited observations
Direct measurements in northern Alaska are limited, making it difficult to understand how individual rivers will respond to warming.
“What makes this question so difficult to answer is that direct observations are very sparse in northern Alaska,” says Rollins, an extension associate professor of Earth, Geography, and Climate Sciences at the University of Massachusetts Amherst. “There are not enough river sample measurements anywhere to quantify the flow into estuaries along the entire North Slope of Alaska.”
To address this gap, Rollins has developed a permafrost water balance model over the past 25 years. The model estimates key processes such as snow accumulation, melting, and active layer changes to better represent real-world conditions. In 2021, it was expanded to simulate dissolved organic carbon, and in 2024 it was applied to the entire 22.45 million square kilometer Arctic region.
The model suggests that over the next 80 years, runoff could increase by up to 25% in the Arctic, groundflow could increase by 30%, and southern regions could become drier.
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 more granular scale.
“We have typically run models in 25-kilometer grid cells,” Rollins says. “This new study is the first to image such a large area of the Wisconsin-sized Arctic, 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 significant computing power. Each simulation took 10 consecutive days on a supercomputer at the Massachusetts Green High Performance Computing Center.
“The input of freshwater and DOC into our coastal estuaries will be useful to a wide range of stakeholders interested in the unique ecosystems of the northern Alaska coast, including the Beaufort Lagoon Ecosystem Project, which will help us quantify exactly what comes in from these coastal estuaries,” Rollins said.
Northwest Alaska has the most carbon gain
The researchers found that while runoff and melting are increasing across the region, the largest increases in carbon export are occurring in northwestern Alaska.
“It’s flatter there,” Rollins said. “That means there’s much more carbon from decaying material in the permafrost that has been accumulating for tens of thousands of years. This is ancient carbon. The further east you go, the more mountains you have. The soils are rockier and sandier, and there’s currently less DOC being mobilized as the permafrost thaws.”
Longer snowmelt season drives change
One of the most notable findings is how much of the change is directly tied to permafrost thaw. Now the thaw season is longer than before, lasting until September and even October.
These changes may affect salinity, nutrient cycling, and food webs in the Beaufort Sea. Researchers are currently studying how the polygonal shape of ice wedges, a common topographical feature in the Arctic, affects the way water and carbon move toward coastal areas.
Critical gaps in understanding the carbon cycle
“How much DOC reaches the ocean via rivers and streams is part of the carbon cycle, but we don’t know much about it,” Rollins says. “We need more research into these land-sea connections if we are to truly address the issue of global warming and its impact on coastal ecosystems.”
This research was supported by the National Science Foundation and NASA.
