A Landscape Shaped by Ice
The Lena River, after a 4,400-kilometer course across Siberia, forms the largest delta in the Arctic. Spanning about 30,000 square kilometers, this vast, flat plain consists of more than 1,500 islands, 30,000 lakes, and thousands of river channels emptying into the Laptev Sea. For most of the year, the delta is frozen solid. The ground here is a special type of permafrost called Yedoma, an ice-rich sediment dating back to the Pleistocene epoch. Some layers have remained frozen for hundreds of thousands of years. Permafrost in the delta can reach depths of 600 meters.
a notable feature of the Yedoma landscape is its patterned ground. From above, the tundra appears to be covered in a network of massive polygons. These are formed by ice wedges, enormous vertical masses of ice that grow within the soil. During the intensely cold winters, the ground contracts and cracks. In the short summer, meltwater fills these cracks and freezes, widening the fissure. This process repeats over millennia, creating ice wedges that can be several meters across and tens of meters deep. The stress created by these immense ice structures forces the ground into the distinctive polygonal shapes seen today.
A Carbon Bomb with a Lit Fuse
The Yedoma permafrost contains ice, sediment,; it contains a vast quantity of organic material. Trapped within the frozen ground are the remains of countless plants and Pleistocene animals that have been locked away for tens of thousands of years. This ancient permafrost holds almost twice as much carbon as is currently in the atmosphere. As Arctic temperatures rise, the permafrost begins to thaw. Microbes that have been dormant for millennia awaken and begin to decompose this ancient organic matter.
This decomposition releases greenhouse gases, primarily carbon dioxide and methane. In the delta's many thermokarst lakes—bodies of water formed by subsiding ground as the ice within it melts—this process is visibly dramatic. Methane gas bubbles up from the lakebeds, trapped under the winter ice. Scientists can set these bubbles on fire, creating flares that burn for several seconds, shows the potent greenhouse gases escaping the thawing ground. The amount of carbon stored here is so significant that its release is considered a significant positive feedback loop that could accelerate global warming. Research at locations like Sobo-Sise Island shows that erosion of these ice-rich cliffs releases millions of kilograms of organic carbon into the Lena River annually.