Arctic is turning orange

 Toxic shift in Arctic wilderness with orange rivers and could trigger a devastating chain effect

In Alaska’s Brooks Range, rivers once clear enough to drink from now run orange and hazy with toxic metals. As warming thaws formerly frozen ground, it sets off a chemical chain reaction that is poisoning fish and wreaking havoc on ecosystems. Warming soil unleashes metals deadly to fish and food chains. At first glance, the rusty rivers that cut through the Arctic may seem like just a visual curiosity, a curious effect of ice melting under a warming planet. But behind this reddish hue, there is a silent warning. Scientists say what’s happening in Alaska and other polar regions could soon trigger a chain reaction capable of transforming entire ecosystems, from microscopic life in rivers to the global carbon balance. And the most surprising thing is that the culprit isn’t pollution or a mining accident: it’s the ice itself.

As the planet warms, a layer of permafrost, permanently frozen Arctic soil which locked away minerals for millennia, is beginning to thaw. Water and oxygen creep into the newly exposed soil, triggering the breakdown of sulphide-rich rocks, and creating sulphuric acid which leaches naturally occurring metals like iron, cadmium and aluminium from rocks into the river. When researchers first flew over Alaska’s Kutuk River, they were struck by its colour. The once-crystalline waters had turned a deep orange, stretching for miles across the permafrost plains. The same hue now stains at least 75 other streams in the Brooks Range. For years, climate change was suspected. But the question lingered: how could melting ice cause rivers to rust? Often times, geochemical reactions like these are triggered by mining operations. But that is not the case this time. “This is what acid mine drainage looks like,” said Tim Lyons, a biogeochemist at the University of California, Riverside. “But here, there’s no mine. The permafrost is thawing and changing the chemistry of the landscape.” The answer began to emerge when a team from Umeå University, in Sweden, done a study, revealing that frozen water can trigger stronger chemical reactions than liquid water. As ice forms, it creates microscopic pockets of liquid water between the crystals, which function as highly acidic mini-chemical reactors, capable of dissolving iron minerals even at -30°C. What scientists discovered next was alarming. Each freeze-thaw cycle, now more frequent due to global warming, releases iron, copper and zinc from the soil into rivers. When these metals come into contact with the air, they oxidize and stain the water rusty.

The Salmon River, described as “the purest, most crystal-clear water, is now a chemical cocktail. Since 2019, its waters have taken on shades of orange and yellow, reminiscent of acidic mining waste, except there are no mines nearby. Researchers have identified the real culprit: melting permafrost. Ecologist Paddy Sullivan of the University of Alaska Anchorage has identified more than 500 sites where acidic water escapes from the frozen ground, destroying vegetation before reaching waterways. Though the study focuses on the Salmon River, researchers warn that similar transformations are already underway across dozens of other Arctic watersheds. “I have worked and travelled in the Brooks Range since 1976, and the recent changes in landforms and water chemistry are truly astounding,” said David Cooper, Colorado State University research scientist and study co-author. Remember that between 2022 and 2023, measurements showed concentrations of iron, copper and nickel up to 37 times higher than ten years ago, levels capable of eliminating aquatic insects, such as mayflies and plecoptera, the base of the fish food chain. Without them, salmon populations began to plummet. Even though the local limestone helps neutralize some of the acidity, the metals remain, permeating the sediments and slowly poisoning ecosystems. This discovery even reminds us of those radioactive lakes in the US where strange life thrives. Ecologist Paddy Sullivan of the University of Alaska first noticed the dramatic changes in 2019 while conducting fieldwork on Arctic forests shifting northward, another consequence of climate change. A pilot flying Sullivan into the field warned him the Salmon River hadn’t cleared up after the snowmelt and looked “like sewage.” Alarmed by what he saw, Sullivan joined forces with Lyons, Roman Dial from Alaska Pacific University, and others to investigate the causes and ecological consequences. 

The analysis confirmed that thawing permafrost was unleashing geochemical reactions that oxidize sulphide-rich rocks like pyrite, generating acidity and mobilizing a wide suite of metals, including cadmium, which accumulates in fish organs and could affect animals like bears and birds which eat fish. The Arctic’s orange rivers are just the beginning of the change. At first glance, rusty rivers may seem like a local curiosity, but their impact extends to:-

Permafrost harbours 1.5 trillion tons of carbon. As these layers thaw and oxidize, they can release enormous volumes of CO₂ and methane, further intensifying global warming, the very process that started the problem.

For scientist Rose Cory of the University of Michigan, this phenomenon is “a visible symptom of an invisible chemistry.” In her words: “What we are seeing is the chemical awakening of frozen landscapes that have remained stable for thousands of years.”

In small amounts, metals aren’t necessarily toxic. However, the study shows that levels of metals in the river’s waters exceed US Environmental Protection Agency toxicity thresholds for aquatic life. In addition, the iron-clouded waters reduce the amount of light reaching the bottom of the river and smother insect larvae eaten by the salmon and other fish.

If orange rivers are the first sign, what comes next could redefine the planet’s climate system, and faster than anyone imagined. What began as an aesthetic anomaly has become a planetary alarm, showing how fragile frozen ecosystems are in the face of human heat. It’s no wonder that a strange pink snow spotted in America now turns orange. While current metal concentrations in edible fish tissue are not considered hazardous to humans, the changes to the rivers pose indirect but serious threats. Chum salmon, a key subsistence species for many Indigenous communities, might struggle to spawn in gravel beds choked with fine sediment. Other species, such as grayling and Dolly Varden, may also be affected. “It’s not just a Salmon River story,” Lyons said. “This is happening across the Arctic. Wherever you have the right kind of rock and thawing permafrost, this process can start.” Unlike mine sites, where acid drainage can be mitigated with buffers or containment systems, these remote watersheds might have hundreds of contamination sources and no such infrastructure. Once the chemical process begins, the only thing that can stop it is recovery of the permafrost. “There’s no fixing this once it starts,” Lyons said. “It’s another irreversible shift driven by a warming planet.” The study, funded by the National Science Foundation’s Rapid Response program, highlights the potential danger for other Arctic regions. The researchers would like to help communities and land managers anticipate future impacts and, when possible, prepare for them. “There are few places left on Earth as untouched as these rivers,” Lyons said. “But even here, far from cities and highways, the fingerprint of global warming is unmistakable. No place is spared.”