Josh Koch, U.S. Geological Survey
A new study challenges the long-standing assumption that frozen conditions slow chemical activity, offering fresh insight into the mysterious orange tint of Arctic rivers. The research reveals that ice can actually outperform liquid water in extracting iron from common minerals.
Arctic Rivers Turning Orange
Over recent years, rivers across the Arctic have taken on an orange hue as thawing permafrost, driven by rising temperatures, has released iron from local mineral deposits. This excess iron not only colors the rivers but also reduces dissolved oxygen levels and raises acidity, creating hostile conditions for aquatic life.
Previously, scientists thought iron trapped in icy deposits remained stable. However, researchers at Umeå University in Sweden found that ice is surprisingly more effective than melting permafrost in releasing iron. Their experiments showed that ice at –10 °C (14 °F) liberated more iron from mineral samples than liquid water at 4 °C (39.2 °F).
Ice as a Chemical Reactor
“Ice isn’t just an inert frozen block,” explains co-author Jean-François Boily. “As it freezes, microscopic pockets of liquid water form between ice crystals. These tiny chambers act like chemical reactors where compounds concentrate and become highly acidic, allowing them to interact with iron minerals even at temperatures as low as –30 °C.”
The team tested goethite—a mineral combining iron oxide with soils and sediments—exposed to an organic acid. They found that not only did frozen water release more iron than liquid water, but repeated cycles of freezing and thawing proved to be the most effective at extracting it. Freshwater and brackish water promoted this release, while seawater inhibited it.
Climate Change and Freeze-Thaw Cycles
“With a warming climate, freeze-thaw events are happening more often,” notes lead author Angelo Pio Sebaaly. “Each cycle adds more iron from soils and permafrost to surrounding waters, potentially altering water chemistry and ecosystems on a large scale.”
So far, the research has focused on acidic conditions similar to those near mining sites. The next step is to examine how ice-driven processes influence iron release in other environments. These findings could reshape how environmental scientists view the orange river phenomenon and its consequences for wildlife.
Read the original article on: New Atlas
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