Long-Term Release of Carbon Dioxide from Arctic Tundra Ecosystems in Alaska
Releases of the greenhouse gases carbon dioxide (CO2) and methane (CH4) from thawing permafrost are expected to be among the largest feedbacks to climate from arctic ecosystems. However, the current net carbon (C) balance of terrestrial arctic ecosystems is unknown. Recent studies suggest that these ecosystems are sources, sinks, or approximately in balance at present. This uncertainty arises because there are few long-term continuous measurements of arctic tundra CO2 fluxes over the full annual cycle. Here, we describe a pattern of CO2 loss based on the longest continuous record of direct measurements of CO2 fluxes in the Alaskan Arctic, from two representative tundra ecosystems, wet sedge and heath tundra. We also report on a shorter time series of continuous measurements from a third ecosystem, tussock tundra. The amount of CO2 loss from both heath and wet sedge ecosystems was related to the timing of freeze-up of the soil active layer in the fall. Wet sedge tundra lost the most CO2 during the anomalously warm autumn periods of September–December 2013–2015, with CH4 emissions contributing little to the overall C budget. Losses of C translated to approximately 4.1 and 1.4% of the total soil C stocks in active layer of the wet sedge and heath tundra, respectively, from 2008 to 2015. Increases in air temperature and soil temperatures at all depths may trigger a new trajectory of CO2 release, which will be a significant feedback to further warming if it is representative of larger areas of the Arctic.
Keywordsarctic tundra net ecosystem exchange permafrost soil temperature carbon dioxide methane
- Amiro BD et al. 2010. Ecosystem carbon dioxide fluxes after disturbance in forests of North America. J Geophys Res 115 (G4). doi:10.1029/2010JG001390.
- Björkman MP et al. 2010. Winter carbon dioxide effluxes from Arctic ecosystems: an overview and comparison of methodologies. Global Biogeochem Cycles 24(GB3010):1–10.Google Scholar
- Burba GG, Anderson DA. 2010. Brief Practical Guide to Eddy Covariance Flux Measurements: Principles and Workflow Examples for Scientific and Industrial Applications. Lincoln, NE: LI-COR.Google Scholar
- Chang Y-W et al. 2104. Methane emissions from Alaska in 2012 from CARVE airborne observations. Proc Natl Acad Sci USA 111:16694–9.Google Scholar
- Efron B, Tibshirani R. 1998. An Introduction to the Bootstrap. Boca Raton: Chapman and Hall.Google Scholar
- Jorgenson MT, Heiner M. 2004. Ecosystems of Northern Alaska. ABR, Inc. and The Nature Conservancy, Anchorage, AK.Google Scholar
- Karhu K et al. 2014. Temperature sensitivity of soil respiration rates enhanced by microbial community response. Nature 513:81–4.Google Scholar
- Inc LI-COR. 2004. LI-7500 CO2/H2O Analyzer Instruction Manual. Lincoln, NE: LI-COR.Google Scholar
- Inc LI-COR. 2009. LI-7500A Open-path CO2/H2O Open Path Gas Analyzer Instruction Manual. Lincoln, NE: LI-COR.Google Scholar
- Inc LI-COR. 2010a. LI-7200 CO2/H2O Analyzer Instruction Manual. Lincoln, NE: LI-COR.Google Scholar
- Inc LI-COR. 2010b. LI-7700 Open Path CH4 Analyzer Instruction Manual. Lincoln, NE: LI-COR.Google Scholar
- LI-COR Inc. 2013. EddyPro® 4.2 Help and User’s Guide. (LI-COR, Inc. Lincoln, Nebraska).Google Scholar
- Myhre GD et al. 2013. Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker TF, and others (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York.Google Scholar
- Romanovsky VE, Sergueev DO, Osterkamp TE. 2003. Temporal variations in the active layer and near-surface permafrost temperatures at the long-term observatories in Northern Alaska. In: Phillips M, Springman S, Arenson LU, Eds. Permafrost. Lisse: Swets & Zeitlinger. p 989–94.Google Scholar
- von Fischer JC, Rhew RC, Ames GM, Fosdick BK, von Fischer PE. 2010. Vegetation height and other controls of spatial variability in methane emissions from the Arctic coastal tundra at Barrow. Alaska. J Geophys Res 115. doi:10.1029/2009JG001283.
- Webb EE et al. 2016. Increased wintertime CO2 loss as a result of sustained tundra warming. J Geophys Res 121. doi:10.1002/2014JG002795.