Thermokarst – Thawing Permafrost
Join scientists Jason Dobkowski and Collin Ward on the shores of Wolverine Lake, near the remote foothills of the Brooks Range, North Slope Alaska. They’re studying a permafrost thaw slump. Ground that collapsed is now depositing silt and mud into the remote lake.
Permafrost is perennially frozen ground, or ground that has stayed frozen for at least two years. It provides the infrastructure of Arctic ground. Most occurs north of the Arctic Circle. Yet even in Fairbank there is permafrost which has been frozen for the last several thousand years.
The permafrost on the Alaskan Arctic Plain sits in temperatures as cold as 12 to 16°F [-11 to -9°C] and measures up to 2,132 feet [650 meters] thick.
Now Earth’s temperature is warming, and the Arctic is warming faster than anywhere else. In the last 50 years alone, the Arctic has warmed on average 1.8°F [1ºC], from 35.6 – 37.4°F [2 - 3°C]. Pre- Industrial Revolution there were 560 gigatons of carbon in the atmosphere (1 gigaton = 1 billion tons). With additions since then, we’ve reached 760 gigatons. Frozen in permafrost waits an estimated 1,400 – 1,600 gigatons of carbon; twice as much carbon as that currently residing in Earth’s atmosphere.
Permafrost is melting. And as underground ice melts, the ancient organic matter frozen in permafrost thaws. At the site of permafrost failures you’ll find thermokarst.
Thermokarsts mark uneven, shifted ground. On slopes, destabilized permafrost can cause massive land slides that move tons or even hundreds of thousands of tons of soil. On more level land the ground subsides, settling into empty spaces vacated by ice, forming sinkholes and massive depressions surrounded by unpredictable hillocks. Permafrost failure events can result in gullies hundreds of feet across or long, and tens of feet deep.
Water flows through these thermokarst features, encouraging erosion and making the thawed permafrost material move. What happens when ancient carbon and nutrients are reintroduced into the Arctic ecosystem, and the global carbon cycle? Thermokarst scientists are working to find out.
✧The ground changing under our feet – Thermokarsts (Laura Nielsen) Thermokarst, Permafrost, Climate Change
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