A few minutes of freezing can change the fate of iron in nature
Just a few minutes of freezing and thawing can have a decisive impact on how ferrihydrite, the most reactive iron mineral in cold soils, permafrost and glaciers, transforms, according to researchers at Umeå University. As climate warming intensifies freeze-thaw cycles and extends them into new regions, ice is becoming an increasingly important driver of Earth's ecosystems.
A mere few minutes of freezing and thawing can significantly alter the fate of iron in nature, according to researchers at Umeå University. Just a brief exposure to ice can have a profound impact on the transformation of ferrihydrite, the most reactive iron mineral in cold soils, permafrost, and glaciers. As climate warming intensifies, freeze-thaw cycles extend into new regions, making ice an increasingly important driver of Earth's ecosystems.
Ice is far from a passive freezer; it is an active geochemical reactor that can swiftly change the properties of iron minerals. Professor Jean-François Boily of Umeå University's Department of Chemistry led the study, published in Science, which reveals that ice plays a more dynamic role than previously thought.
Freezing water creates microscopic pockets of liquid between growing ice crystals, concentrating substances that cannot be incorporated into the ice. When ferrihydrite particles are confined in these pockets, the force that draws unfrozen water toward the advancing ice front presses them together, stripping away the surrounding water and hydroxyl groups.
This results in the particles bonding together, becoming much larger aggregates. A single freeze cycle at -20°C increased ferrihydrite particle size by about 30 times, transforming micrometer-sized flakes with flattened shapes inherited from the grain boundaries of the ice.
Further aging in water revealed that ferrihydrite that had never been frozen transformed into goethite, the yellow-brown rust common in cool, moist soils. However, freeze-treated ferrihydrite did not produce goethite and instead transformed into hematite, the red rust associated with warm, dry soils. This shift in mineral formation has far-reaching implications for climate proxies and iron cycling in polar soils.
Understanding the active role of ice as a geochemical reactor is no longer a niche concern but a central challenge in comprehending the geochemical cycling of iron at Earth's surface.
Written by urgent.news from Phys.org's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
