Siberia's 'Carbon Bomb'

Microbial decomposition generates its own heat, a phenomenon Sergei Zimov and colleagues explored in permafrost soils in a 2001 Russian publication. Dmitry Khvorostyanov and Philippe Ciais of the Laboratoire des Sciences du Climat et de l'Environment (LSCE) in Paris recently incorporated this microbial heating effect into a model of the carbon and heat budget of yedoma soils. They found that atmospheric warming can kick-start a microbial engine that thaws the entire frozen soil column tens of meters deep, seen in the left panel as a transition from cool colors to warm colors around model year 30 (the time period represented by the horizontal axis is arbitrary). The heating is fueled by the decomposition of the organic matter in the process, seen in the right panel where soils transition from high soil carbon (black) to low soil carbon (white). Once the organic matter that fuels the microbes is exhausted, the soils freeze again, but with only a fraction of the carbon left. The whole process takes only about 100 years to complete and begins when just 10 percent of the organic matter has decomposed.