Freeze Thaw Fig 1 ice crystals from permafrost cores in Alaska E Rooney x600.jpg

Ice crystals formed on the outside of a soil sample taken from Alaska’s permafrost. (Photo by Erin Rooney.)

Winter soil freezes, heaves and moves. The Soil Science Society of America Jan. 15 Soils Matter blog looks at the freeze-thaw cycle, how it changes soil on a microscopic level, and the reaction of Alaska’s unique permafrost soils.

“Freezing deforms the soil,” writes blogger Erin Rooney. “Frost heaving allows mineral subsurface layers–or horizons–to be squeezed up through the soil. This moves horizons from lower to higher. This feature is known as a ‘mud boil’ or ‘frost boil.’” Rooney is a graduate fellow at Oregon State University.

But the icy drama doesn’t stop with what human eyes can see. The cracks, freezing, and expansion can occur on a tiny scale as well. This can release minerals and further change the soil’s composition.

In the case of Alaska’s permafrost soils, the changes may keep coming. “These soils have stored an estimated 40 percent of Earth’s terrestrial organic carbon for centuries. The soil’s ability to continue storing carbon belowground will depend on soil resilience to changes in the climate. These changes include increasing variability in winter air temperature and the resulting increase in freeze-thaw cycles.”

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