Quantifying the effect size of changing environmental controls on carbon release from permafrost-affected soils

Monday, 15 December 2014: 4:30 PM
Christina Schaedel1, Martin K. F. Bader2, Edward A G Schuur3, Rosvel G Bracho1, Petr Capek4, Sarah L De Baets5, Katka Diakova4, Jessica Gilman Ernakovich6, Iain P Hartley5, Colleen M. Iversen7, Evan S Kane8, Christian Knoblauch9, Massimo Lupascu10, Susan Natali11, Richard J Norby12, Jonathan A. O'Donnell13, Taniya Roy Chowdhury12, Hana Santruckova4, Gaius R Shaver14, Victoria L Sloan15, Claire C Treat16 and Mark P Waldrop17, (1)University of Florida, Gainesville, FL, United States, (2)New Zealand Forest Research Institute, Rotorua, New Zealand, (3)Univ Florida, Gainesville, FL, United States, (4)University of South Bohemia, Ceske Budejovice, Czech Republic, (5)University of Exeter, Exeter, United Kingdom, (6)Division of Land and Water, CSIRO, Glen Osmond, Australia, (7)Oak Ridge National Laboratory, Oak Ridge, TN, United States, (8)Michigan Tech Univ--SFRES, Hancock, MI, United States, (9)University of Hamburg, Institute of Soil Science, Hamburg, Germany, (10)Univ of California, Irvine, Irvine, CA, United States, (11)Woods Hole Science Center Falmouth, Falmouth, MA, United States, (12)Oak Ridge National Lab, Oak Ridge, TN, United States, (13)National Park Service Anchorage, Anchorage, AK, United States, (14)Marine Bio Lab, Woods Hole, MA, United States, (15)ORNL, Bristol, United Kingdom, (16)University of Alaska Fairbanks, Fairbanks, AK, United States, (17)US Geological Survey, Menlo Park, CA, United States
High-latitude surface air temperatures are rising twice as fast as the global mean, causing permafrost to thaw and thereby exposing large quantities of previously frozen organic carbon (C) to microbial decomposition. Increasing temperatures in high latitude ecosystems not only increase C emissions from previously frozen C in permafrost but also indirectly affect the C cycle through changes in regional and local hydrology. Warmer temperatures increase thawing of ice-rich permafrost, causing land surface subsidence where soils become waterlogged, anoxic conditions prevail and C is released in form of anaerobic CO2 and CH4. Although substrate quality, physical protection, and nutrient availability affect C decomposition, increasing temperatures and changes in surface and sub-surface hydrology are likely the dominant factors affecting the rate and form of C release from permafrost; however, their effect size on C release is poorly quantified. We have compiled a database of 24 incubation studies with soils from active layer and permafrost from across the entire permafrost zone to quantify a) the effect size of increasing temperatures and b) the changes from aerobic to anaerobic environmental soil conditions on C release. Results from two different meta-analyses show that a 10°C increase in temperature increased C release by a factor of two in boreal forest, peatland and tundra ecosystems. Under aerobic incubation conditions, soils released on average three times more C than under anaerobic conditions with large variation among the different ecosystems. While peatlands showed similar amounts of C release under aerobic and anaerobic soil conditions, tundra and boreal forest ecosystems released up to 8 times more C under anoxic conditions. This pan-arctic synthesis shows that boreal forest and tundra soils will have a larger impact on climate change when newly thawed permafrost C decomposes in an aerobic environment compared to an anaerobic environment even when accounting for the higher heat trapping capacity of CH4 over a 100-year timescale.