Melting Arctic rivers could unleash carbon equal to millions of cars

Recent research sheds unprecedented light on the Arctic’s delicate balance, revealing the pivotal role of permafrost in sculpting the region’s river systems and its potential impact on global carbon emissions under the threat of climate change.

This study, spearheaded by Dartmouth College, marks a significant advancement in our understanding of Arctic landscapes, with profound implications for our approach to environmental stewardship and climate policy.

Frozen menace: Permafrost and Arctic rivers

Permafrost, a dense layer of soil that remains frozen for at least two consecutive years, dictates why Arctic rivers are confined to narrower and shallower valleys compared to their southern counterparts.

This discovery is pivotal, shedding light on the nuanced interactions between the Earth’s surface and its climatic forces.

However, the study also raises concerns about the vulnerability of permafrost in the face of global warming.

The researchers estimate that for every 1.8 degrees Fahrenheit (1 degree Celsius) increase in global temperature, the carbon released from thawing Arctic soil could equate to the annual emissions of 35 million cars.

Delicate balance of Arctic landscapes

This potential release of carbon, as permafrost weakens and polar waterways expand, may trigger a feedback loop of warming, exacerbating the release of greenhouse gases.

Joanmarie Del Vecchio, the study’s lead author, explains, “The whole surface of the Earth is in a tug of a war between processes such as hillslopes that smooth the landscape and forces like rivers that carve them up.”

Del Vecchio, who spearheaded this research during her tenure as a Neukom Postdoctoral Fellow at Dartmouth, alongside advisors Marisa Palucis and Colin Meyer, highlights the complexity of predicting outcomes when freeze-thaw cycles are involved.

The balance between these forces could either sequester carbon within the soil or release it into the atmosphere, significantly impacting climate change dynamics.

“We understand the physics on a fundamental level, but when things start freezing and thawing, it’s hard to predict which side is going to win,” Del Vecchio said.

Explaining further, “If hillslopes win, they’re going to bury all that carbon trapped in the soil. But if things get warm and suddenly river channels start to win, we’re going to see a large amount of carbon get released into the atmosphere. That will likely create this warming feedback loop that leads to the release of more greenhouse gases.”

Unifying factor in Arctic watersheds

This research was inspired by Del Vecchio’s observations during a 2019 fieldwork expedition in Alaska. Ascending from a riverside worksite, she was struck by the dominance of hillslopes over river channels, a landscape seemingly shaped by temperature variations.

“It seemed like the hillslopes were winning and the channels were losing,” Del Vecchio said. “We wanted to test whether it was temperature shaping this landscape. We’re very lucky to have had the amount of surface and digital elevation data that’s been produced in the past few years. We couldn’t have done this study a few years ago.”

With the advent of sophisticated surface and digital elevation data in recent years, the team embarked on a comprehensive analysis, examining over 69,000 watersheds across the Northern Hemisphere, from the Tropic of Cancer to the North Pole.

Utilizing satellite and climate data, they assessed the rivers’ channel networks within their watersheds, alongside the steepness of river valleys.

Their findings were revealing: 47% of the watersheds studied are influenced by permafrost. These areas exhibit deeper and steeper river valleys, with 20% less of their landscape occupied by river channels compared to temperate watersheds.

This uniformity exists despite varying factors like glacial history, topography, precipitation, and others that typically influence the interplay of water and land. It underscores a crucial point: Arctic watersheds are primarily shaped by permafrost.

“Any way we sliced it, regions with larger, more plentiful river channels are warmer with a higher average temperature and less permafrost,” Del Vecchio elaborated. “You need a lot more water to carve valleys in areas with permafrost.”

Releasing permafrost carbon into Arctic rivers

The Arctic has experienced a warming of over 3.6 degrees Fahrenheit (2 degrees Celsius) above pre-industrial levels, significantly impacting the permafrost and, consequently, the carbon stored within.

The research team estimates that the gradual thawing of Arctic permafrost could release between 22 billion and 432 billion tons of carbon dioxide by 2100 if greenhouse gas emissions are curbed.

Without emission reductions, the release could soar to as much as 550 billion tons, juxtaposed against the 36 billion tons of carbon dioxide from energy consumption recorded in 2022, a historical peak.

Marisa Palucis, reflecting on her Arctic research trips, shared insights into the delicate balance of the Arctic landscape.

She recounted witnessing the dramatic break-off of a chunk of bedrock, an event triggered by the seemingly minor act of water flow, emphasizing the profound impact even small changes can have on this cold-adapted environment.

“This is a landscape that is adapted to colder conditions, so when you change it, even a small amount of water flowing through rock is sufficient to cause substantial change,” Palucis remarked, illustrating the vulnerability of the Arctic to climatic shifts.

Understanding Arctic climate dynamics

Palucis also noted the broader implications for our understanding of Arctic landscapes, comparing current knowledge to that of temperate landscapes a century ago.

“Our understanding of Arctic landscapes is more or less where we were with temperate landscapes 100 years ago,” she stated, stressing that existing models for temperate watersheds cannot be directly applied to polar regions. This realization opens new avenues for research and understanding of these unique environments.

Adding historical context, Del Vecchio mentioned sediment cores from the Arctic that indicate extensive soil runoff and carbon deposits from around 10,000 years ago, suggesting that the region was much warmer in the past.

The unknown future of a warming Arctic

This historical evidence, combined with current observations, suggests an increasing trend of water channels in a warming Arctic, yet the full impact of rapid temperature increases on these landscapes remains uncertain.

“We have some evidence from the past that a lot of sediment was released into the ocean when there was warming,” Del Vecchio said, encapsulating this uncertainty.

“And now we have a snapshot from our paper showing the Arctic will get more water channels as it gets warmer. But none of that is the same as saying, ‘This is what happens when you take a cold landscape and turn up the temperature real fast.’ I don’t think we know how it will change.”

In summary, this research underscores the intricate relationship between permafrost, river systems, and climate change in the Arctic.

As permafrost thaws, releasing previously trapped carbon into the atmosphere, the consequences extend beyond the Arctic, contributing to global climate change.

The observations and insights from Dartmouth’s study serve as a crucial step towards understanding and potentially mitigating these far-reaching impacts.

The full study was published in the journal Proceedings of the National Academy of Sciences.

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