Scientists have long been concerned about the potential for climate warming to unlock vast reservoirs of carbon dioxide (CO2) from frozen Arctic soils – aka permafrost. Just how quickly all that CO2 might be released into the atmosphere, and precisely by what mechanism or mechanisms, have been questions of growing interest among researchers and potentially crucial importance for governments, policymakers and societies the world over.
A study believed to be the first of its kind has established a direct link between the action of microbes and the rapid release of CO2 from ¨Yedoma¨ permafrost soils in northern Alaska deposited 35,800 years ago during the Pleistocene Epoch. Researchers from the U.S. Geological Survey (USGS), the University of Colorado, Boulder and Florida State University found that upon thawing decomposition of organic compounds in them by microbes resulted in a rapid, 53-percent decrease in the average concentration of dissolved organic carbon (DOC) and a seven-fold increase in the average concentration of dissolved inorganic compounds.
Microbes munch on thawing on Arctic permafrost
Arctic permafrost soils store the equivalent of more than twice the amount of CO2 than is present in the atmosphere, according to scientists' best estimates. If global mean temperatures continue to rise at the current rate, these soils will thaw out, leaving the dissolved organic carbon in them accessible to microbes. Feasting on this DOC, the microbes would add huge quantities of CO2 to the atmosphere, thereby exacerbating climate warming.
By 2100, the research team projects that at current rates of warming microbial decomposition of DOC in Yedoma permafrost soils would result in the release of 5-10 teragrams (Tg, 109 kilograms) of DOC per year. That represents 19-26 percent of all the DOC transported by Arctic rivers. Scientists have yet to detect a surge in DOCs transported in these rivers, however, which suggests the CO2 is being decomposed by microbes and released into the atmosphere before ever reaching them.
To determine the amount of and rate at which microbes ¨mineralized¨ DOC to CO2 in ¨Yedoma¨ permafrost, the scientists placed samples in a ¨high-temporal-resolution bioreactor¨ for 200 hours. Publishing the results in an October 26 online early edition of the Proceedings of the National Academy of Sciences (PNAS), the experiments are said to be the first to put hard numbers on the high CO2 production rates of low-molecular-weight (LMW) DOC resulting from microbial action.
Furthermore, the research team found that 87 percent of the DOC metabolized and released by microbes as CO2 came from LMW organic acids. The observed rates of loss of DOC, moreover, are among the highest reported for permafrost carbon. Additionally, they ¨demonstrate the potential importance of LMW DOC in driving the rapid metabolism of Pleistocene-age permafrost carbon upon thaw and the outgassing of CO2 to the atmosphere by soils and nearly inland waters,¨ the report authors highlighted.