This finding might be shocking, but at the same time, quite understandable: Ice, is not just a “sleeping” blok. A team for the Umeå University (in Sweden) showed in a study published in PNAS, that ice can accelerate chemical reactions capable of dissolving iron minerals even at -30°C. Turns out, that when they freeze, water leaves tiny liquid pockets between the crystals. And this micro spaces, are molecules concentrates so much in fact that the chemicals “accelerate.”
The study was centered goethite (a form of iron oxide present in soils and rocks) and mixed with oxalate (common organic acid in plants and soils). The result was that even below zero degrees, the iron passes into the water and then oxidizes, dyeing the currents of an orange-ish tone.
This phenomenon help explain why some Artic rivers are becoming of on oxide color and what’s happening in cold landscapes with permafrost. Guiding the study there are Jean-François Boily and Angelo Pio Sebaaly, and there message to us is that this reactions will he’s understand how to take care of the north ecosystem and better interprete climate change signals involving carbon cycles.
How ice works: Chemistry in tiny spaces
When water defrost, it expels impurities into small liquid pockets. In those corners everything is concentrated: ions, acids and salts. That concentration changes the pH and multiplies the shocks between molecules, which accelerates the chemical reaction.
In the laboratory, researchers observed that at –10 °C, the ice melt more iron since goethite than the liquid water at 4 °C. What does this means? Extreme cold wind’t stop the reaction, it actually pushed it. In some tests there was activity even at –30 °C. The role of oxalate is key, because it helps to release iron from the mineral; after that, once in contact with oxygen, that iron turns into iron oxide, the same that gives that red-orange-coffee color to the water.
This behaviour takes down the idea that ice has just “preserves” something, and shows that is in fact a chemical actor capable of transforming its surroundings.
From the laboratory to the landscape: why some rivers look “rusty”
The study also looked at the freezing and defrosting cycles. Every time the ice melt and transform again, it releases organic compounds that were trapped and feeds new reactions with iron minerals. That way, with every cycle, it adds up more soluble iron to the environment. In nature that iron oxides very fast (and it turns iron oxide) coloring the water.
That’s why some Artic rivers look rusty or oxidazed, it’s not because someone added metals to the water, it’s a natural process that cold favours. Salinity also matters here: the sweet or slightly brackeny water accelerates the dissolution, while the saltier seawater slows it.
Helps understanding the differences between lakes, and coastal zones up the north. And with permafrost, the landscape gets even bigger, because when it defrost, it can release more organic matter and minerals, increasing that same chemical cycle.
It all impacts the ecosystem, changing the chemistry of water, affecting nutrients and oxygen, and altering aquatic life.
A “living” ice in times of change
Climate change is not only about heat. It also intensify the freezing and thaw cycles in cold regions. More cycles mean more opportunities for the ice to work as a natural micro-reactor and release iron and carbon to the environment. This could modify rivers, lakes and soils. But also influence the quality of drinking water in cold areas.
The Umeå University team, continues to test if the same thing happens with other minerals that contain iron. If this is confirmed, ice would have a bigger role than we believed in the planet’s biogeochemical cycles.