Wisconsin-sized chunk of Alaskan permafrost is thawing: Geoscientists say climate may never be the same

Wisconsin-sized chunk of Alaskan permafrost is thawing: Geoscientists say climate may never be the same

In an innovative study, a research team led by geoscientist Michael Rawlins at the University of Massachusetts Amherst has provided unprecedented insights into the consequences of Arctic permafrost thawing. Concentrating on a region of Alaska's North Slope equivalent to the size of Wisconsin—characterized by hundreds of rivers and streams flowing into the Beaufort Sea—the researchers meticulously examined 44 years of climate model data at a one-kilometer grid resolution. Their findings highlight a substantial increase in runoff, enhanced flows of previously frozen carbon through the northern Alaska rivers, and an expansion of the thawing season into late summer and autumn.

The study, recently published in Global Biogeochemical Cycles, significantly enhances our comprehension of the rapid transformations occurring in one of the globe's fastest-warming regions.

Why Arctic rivers matter globally

The role of Arctic rivers in the global ecosystem cannot be overstated. These rivers contribute 11% of the world's river water to an ocean that accounts for a mere 1% of the total ocean volume, underscoring the extreme sensitivity of the Arctic to changes in these watercourses. While the majority of this river water—and the materials it transports—stems from melting snow, the thawing permafrost also substantially influences these dynamics.

The term "permafrost" is somewhat misleading, as it encompasses an "active layer" that undergoes seasonal freeze and thaw cycles each year. In recent decades, the deepening of this active layer, driven by climate warming, has resulted in an increased transfer of groundwater into Arctic rivers.

Moreover, the active layer harbors significant reserves of frozen organic carbon. As this layer deepens, a greater quantity of this carbon, particularly in the form of dissolved organic carbon (DOC), is released into rivers and eventually reaches the ocean.

Notably, the Arctic Ocean disproportionately receives DOC from rivers across the globe, with over 275 million tons of this carbon being converted to carbon dioxide annually. This process contributes to a feedback loop that exacerbates global warming.

From sparse data to supercomputer models

This scenario describes the Arctic as a whole; however, what is occurring with individual rivers or even smaller streams under our changing climate?

"The difficulty in answering this question stems from the limited observational data available in northern Alaska," explains Rawlins, an extension associate professor of Earth, Geographic, and Climate Sciences at UMass Amherst. "There are insufficient river sample measurements to effectively quantify inputs to estuaries along the entire Alaskan North Slope."

To address this challenge, researchers have relied on modeling—leveraging precise simulations to enhance understanding. For the past 25 years, Rawlins has developed the Permafrost Water Balance Model, which estimates a range of data such as snow accumulation, melt patterns, and variations in the active layer to provide the most accurate depiction of field conditions.

In 2021, Rawlins upgraded the model to incorporate simulations of DOC. In 2024, he and his colleagues expanded their modeling to encompass 22.45 million square kilometers of Arctic terrain, anticipating that the region would witness up to a 25% increase in runoff, a 30% rise in subsurface runoff, and a continuously drier southern Arctic over the next 80 years.

"We had previously operated the model on extensive 25-kilometer grid cells," remarks Rawlins. "This study represents the first instance of capturing such a vast area of the Arctic—comparable to Wisconsin—at a kilometer scale, while examining data over an extended timeframe: our model simulates daily river flows and coastal exports over 44 years, from 1980 to 2023."

The supercomputer at the Massachusetts Green High Performance Computing Center requires 10 consecutive days to process the complete data set for each model run, a commitment deemed worthwhile.

"The data on our freshwater and DOC inputs to coastal estuaries will be invaluable to a diverse range of stakeholders invested in these unique ecosystems in coastal northern Alaska," Rawlins asserts, referencing the Beaufort Lagoon Ecosystems project, which is working to quantify the contributions flowing through these coastal estuaries.

Uneven impacts across Arctic landscapes

The research team identified that while thawing and runoff is escalating across the board, the most significant increases in DOC export are observed in northwest Alaska. "The flatter terrain in that area allows for greater accumulation of carbon from decaying organic matter in the permafrost, built up over tens of thousands of years," explains Rawlins.

This carbon is ancient.