It sounds like something out of a science fiction twist: frozen water outperforming its liquid counterpart in breaking down minerals. But that’s exactly what researchers at Sweden’s Umeå University have discovered. In a study published August 26, 2025, in PNAS, scientists found that ice at –10°C releases more iron from goethite—a common iron oxide mineral—than liquid water at 4°C.

A rust-colored river in Alaska’s Brooks Range, where thawing permafrost is releasing iron into the water.  
→ (Image: New Atlas)

This flips a long-held assumption on its head. For decades, scientists believed that cold, frozen environments slowed chemical reactions to a crawl. But as Professor Jean-François Boily explains, “It may sound counterintuitive, but ice is not a passive frozen block.” Instead, freezing creates tiny pockets of liquid water between ice crystals. These micro-reactors become highly acidic, concentrating compounds that aggressively react with iron—even at temperatures as low as –30°C.

Why does this matter? Because it helps explain a troubling trend: Arctic rivers turning rusty orange. As permafrost thaws in a warming climate, iron is being released into waterways at unprecedented rates. These rivers, like those in Alaska’s Brooks Range, are becoming more acidic and oxygen-poor, making it harder for fish and other aquatic life to survive.

The team studied goethite alongside a naturally occurring organic acid, simulating conditions found in Arctic soils. They discovered that repeated freeze-thaw cycles—common in warming climates—supercharge the iron release. Each cycle not only breaks down minerals but also unleashes organic compounds trapped in the ice, fueling further reactions.

Water salinity adds another twist. Fresh and brackish water accelerate iron dissolution, while seawater tends to suppress it. That means coastal regions with mixed water sources could see more dramatic changes than previously expected.

This isn’t just about rivers changing color. It’s about the ripple effects across ecosystems. Iron overload can disrupt aquatic food chains, degrade water quality, and even influence carbon cycling. And with freeze-thaw cycles becoming more frequent due to climate change, these reactions could intensify across polar and mountainous regions.

Doctoral researcher Angelo Pio Sebaaly, lead author of the study, puts it plainly: “Each cycle releases iron from soils and permafrost into the water. This can affect water quality and aquatic ecosystems across vast areas.”

The implications stretch beyond the Arctic. Acidic environments like mine drainage sites, frozen dust in the atmosphere, and acid sulfate soils along the Baltic coast could all be affected. Ice, once thought to be a quiet bystander, is proving to be a chemical instigator.

So what’s next? The Boily lab is now investigating whether this iron-releasing behavior holds true across all types of iron-bearing ice. If it does, environmental scientists may need to rethink how they model pollution, climate feedback loops, and ecosystem resilience.

In a world where climate change is rewriting the rules, this study reminds us that even ice has a story to tell—and it’s more active, acidic, and impactful than we ever imagined.

Source: New Atlas