Researchers have long believed that frozen environments slow chemical reactions, but new research challenges this belief.
In a study published last month in the journal PNAS, researchers have demonstrated that ice can dissolve iron minerals better than liquid water, with implications for the many Arctic rivers mysteriously turning orange as the planet warms.
Specifically, Jean-François Boily, a co-author of the study and a chemist at Umeå University, and his colleagues revealed that ice at 14 degrees Fahrenheit (-10 degrees Celsius) unlocks more iron from common minerals than liquid water at 39 degrees Fahrenheit (4 degrees Celsius).
Iron dissolves more efficiently
“It may sound counterintuitive, but ice is not a passive frozen block,” Boily said in a university statement. “Freezing creates microscopic pockets of liquid water between ice crystals. These act like chemical reactors, where compounds become concentrated and extremely acidic. This means they can react with iron minerals even at temperatures as low as minus 30 degrees Celsius.”
They investigated goethite (a common iron oxide mineral) with a natural organic acid, revealing that repeated cycles of freezing and thawing dissolve the iron more efficiently. That’s because organic compounds formerly trapped in the ice are released during the freezing and thawing, generating additional chemical reactions. The team also noted that while brackish and fresh water furthered the dissolution, salty seawater can subdue it.
These results carry important applications for acidic environments, according to the researchers, including mine drainage sites, frozen dust in the atmosphere, acid sulfate soils on the coast of the Baltic Sea, or any acidic frozen environment where iron minerals and organics interact. Moving forward, Boily and researchers are working to discover whether their results apply to all ice containing iron.
“As the climate warms, freeze-thaw cycles become more frequent,” said Angelo Pio Sebaaly, a graduate student in chemistry at the university and first author of the study. “Each cycle releases iron from soils and permafrost into the water. This can affect water quality and aquatic ecosystems across vast areas.”
Ice is an active player
Notably, it might also have something to do with why rivers in the Arctic are turning an alarming orange. “By resolving the chemical controls on mineral dissolution in ice, this work can help explain how freeze-thaw events are supplying new fluxes of soluble iron to nature,” the researchers wrote in the study.
The paper also highlights ice as an “active player,” according to the statement, as opposed to a “passive storage medium,” confirming yet another element we should keep a close eye on as climate change disrupts environments around the world.
