The world’s permafrost holds vast stores of carbon. What happens when it thaws?

Like a giant dragonfly, the chopper skims over undulating swaths of tussocky tundra, then touches down at Wolverine Lake, one of a swarm of kettle lakes near the Toolik Field Station on Alaska’s North Slope. Even before the blades stop spinning, Rose Cory, an aquatic geochemist from the University of Michigan in Ann Arbor, gracefully swings to the ground and beelines to the spot where, four years ago, a subterranean block of ice began to melt, causing the steep, sloping bank to slump into the water. The lake throws back a somber reflection of the clouds swirling above, its surface riffled by the wind.

Cory is here because the slump provides a vivid example of the ordinarily inaccessible stuff she studies. Slick with meltwater, the chocolaty goop brims with microscopic bits of once-living things that have not touched sunlight or air or flowing water for centuries, perhaps millennia. Deeper still lie plant and animal remains that could be tens of thousands of years old, dating back to the Pleistocene, when steppe bison and woolly mammoths wandered a treeless region that extended from here across the Bering Land Bridge, all the way to Siberia.

To those like Cory who know how to parse it, this slump is a source of wonder. It offers a tantalizing portal into the hidden world of permafrost, the broad band of perpetually frozen soils that undergirds a circumpolar region more than twice the size of the continental U.S. This region is now warming at twice the rate of the global average, with grave implications for the stability of permafrost and all it holds. Both small and large things are poised to emerge from this gelid domain, from common soil-dwelling bacteria, to the nearly intact carcasses of Ice Age megafauna. The most important, however, is the carbon stored in the frozen layers of leaves, stems and roots that lie beneath our feet.

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