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Large CO2 and CH4 Emissions from Polygonal Tundra During Spring Thaw in Northern Alaska Naama Raz-Yaseef Lawrence Berkeley National Laboratory

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Large CO2 and CH4 Emissions from Polygonal Tundra During Spring Thaw in Northern Alaska Naama Raz-Yaseef Lawrence Berkeley National Laboratory University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Biological Systems Engineering: Papers and Biological Systems Engineering Publications 2017 Large CO2 and CH4 emissions from polygonal tundra during spring thaw in northern Alaska Naama Raz-Yaseef Lawrence Berkeley National Laboratory Margaret S. Torn Lawrence Berkeley National Laboratory Yuxin Wu Lawrence Berkeley National Laboratory David P. Billesbach University of Nebraska-Lincoln, [email protected] Anna K. Liljedahl University of Alaska Fairbanks See next page for additional authors Follow this and additional works at: http://digitalcommons.unl.edu/biosysengfacpub Part of the Bioresource and Agricultural Engineering Commons, Environmental Engineering Commons, and the Other Civil and Environmental Engineering Commons Raz-Yaseef, Naama; Torn, Margaret S.; Wu, Yuxin; Billesbach, David P.; Liljedahl, Anna K.; Kneafsey, Timothy J.; Romanovsky, Vladimir E.; Cook, David R.; and Wullschleger, Stan D., "Large CO2 and CH4 emissions from polygonal tundra during spring thaw in northern Alaska" (2017). Biological Systems Engineering: Papers and Publications. 482. http://digitalcommons.unl.edu/biosysengfacpub/482 This Article is brought to you for free and open access by the Biological Systems Engineering at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Biological Systems Engineering: Papers and Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Authors Naama Raz-Yaseef, Margaret S. Torn, Yuxin Wu, David P. Billesbach, Anna K. Liljedahl, Timothy J. Kneafsey, Vladimir E. Romanovsky, David R. Cook, and Stan D. Wullschleger This article is available at DigitalCommons@University of Nebraska - Lincoln: http://digitalcommons.unl.edu/biosysengfacpub/482 PUBLICATIONS Geophysical Research Letters RESEARCH LETTER Large CO2 and CH4 emissions from polygonal 10.1002/2016GL071220 tundra during spring thaw in northern Alaska Key Points: Naama Raz-Yaseef1 , Margaret S. Torn1,2 , Yuxin Wu1 , Dave P. Billesbach3 , • Prethaw carbon flux pulses during Anna K. Liljedahl4 , Timothy J. Kneafsey1 , Vladimir E. Romanovsky5 , David R. Cook6 , and thaw offset 46% of CO2 summer 7 uptake and added 6% to CH4 summer Stan D. Wullschleger fluxes • Laboratory experiment linked pulse 1Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA, 2Energy and emissions to a delayed microbial Resources Group, University of California, Berkeley, California, USA, 3Biological Systems Engineering Department, University production mechanism – 4 • of Nebraska Lincoln, Lincoln, Nebraska, USA, Water and Environmental Research Center, University of Alaska Fairbanks, The spring pulse may be a large 5 6 underrepresented source of carbon in Fairbanks, Alaska, USA, Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA, Environmental 7 Arctic regions Science Division, Argonne National Laboratory, Lemont, Illinois, USA, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Correspondence to: Abstract The few prethaw observations of tundra carbon fluxes suggest that there may be large spring N. Raz-Yaseef, [email protected] releases, but little is known about the scale and underlying mechanisms of this phenomenon. To address these questions, we combined ecosystem eddy flux measurements from two towers near Barrow, Alaska, with mechanistic soil-core thawing experiment. During a 2 week period prior to snowmelt in 2014, large Citation: fluxes were measured, reducing net summer uptake of CO by 46% and adding 6% to cumulative CH Raz-Yaseef, N., M. S. Torn, Y. Wu, 2 4 D. P. Billesbach, A. K. Liljedahl, emissions. Emission pulses were linked to unique rain-on-snow events enhancing soil cracking. Controlled T. J. Kneafsey, V. E. Romanovsky, laboratory experiment revealed that as surface ice thaws, an immediate, large pulse of trapped gases is D. R. Cook, and S. D. Wullschleger (2017), emitted. These results suggest that the Arctic CO2 and CH4 spring pulse is a delayed release of biogenic gas Large CO2 and CH4 emissions from polygonal tundra during spring thaw in production from the previous fall and that the pulse can be large enough to offset a significant fraction of the northern Alaska, Geophys. Res. Lett., 44, moderate Arctic tundra carbon sink. 504–513, doi:10.1002/2016GL071220. Received 16 SEP 2016 1. Introduction Accepted 23 NOV 2016 Accepted article online 5 DEC 2016 Pan-Arctic climate has warmed significantly over the last several decades, and end-of-20th-century Arctic Published online 10 JAN 2017 warming exceeded global rates [Spielhagen et al., 2011]. It is estimated that more than ~1300 Pg (Æ1100 Pg) of organic carbon are stored in the frozen tundra [Hugelius et al., 2014], holding the potential for substantial emissions of CO2 and CH4 upon thawing [Schadel et al., 2016], and thus for large positive feedback with climate change [Schuur et al., 2015]. The Arctic is a significant methane source due to the abun- dance of saturated and inundated areas [Walter et al., 2007], and a moderate CO2 sink [Ueyama et al., 2013], but current flux rates are uncertain, as are the controls [McGuire et al., 2012]. One of the challenges in deter- mining the carbon balance of Arctic regions is the difficulty in quantifying winter and shoulder season fluxes, from freeze-in to thaw. While plant CO2 uptake occurs only in the summer, microbial activity can continue for weeks or even months after light and temperature limit photosynthesis [Jansson and Taş, 2014]. Indeed, measurements during the nonsummer months have recently shown that emissions are significant both for CO2 [Oechel et al., 2014] and for CH4 [Zona et al., 2015]. Because of the low biomass and short active season of tundra vegetation, efflux during the winter and shoulder seasons may have significant consequences for annual carbon budgets of the Arctic [Belshe et al., 2013]. Most observational studies of shoulder-season emission pulses have focused on the fall freezeup season for CO2 pulses [Fahnestock, 1999; Bubier et al., 2002], CH4 pulses [Hargreaves et al., 2001; Wille et al., 2008], or a combination of both CO2 and CH4 fall pulses [Tagesson et al., 2012; Mastepanov et al., 2013]. Only a few studies have observed spring-thaw pulses to date, most focusing on episodic CH4 pulses, with even less information available on CO2 pulses. Moore and Knowles [1990] and Windsor et al. [1992] have mea- sured CH4 year-round fluxes in Quebec by using soil chambers and found that episodic spring fluxes increased the annual budget by 7–22%. Song et al. [2012] measured a large spring CH4 pulse with soil cham- bers in China: a 2 day thaw event released CH4 fluxes that were equal to 80% of the active season fluxes. Episodic spring CH4 fluxes measured with soil chambers were also reported by Nykänen et al. [2003] in ©2016. American Geophysical Union. Finland and Tokida et al. [2007] in Japan. Friborg et al. [1997] and Hargreaves et al. [2001] measured CO2 All Rights Reserved. and CH4 fluxes with flux towers in Sweden and Finland, respectively, and reported CH4 spring pulses that RAZ-YASEEF ET AL. SPRING PULSE EMISSION 504 Geophysical Research Letters 10.1002/2016GL071220 were up to 25% of midsummer fluxes and up to 11% of the annual budget, respectively. Friborg et al. À2 À1 [1997] reported CO2 spring fluxes of up to 500 mg m h , but the contribution to the annual budget could not be determined. Others reported on carbon spring fluxes that were small and insignificant (Wille et al. [2008]: flux tower in Siberia, CH4 spring pulses accounted for 3% of the active season flux; Tagesson et al. [2012]: flux tower in Greenland, small CH4 and CO2 flux pulses were detected in spring; and Mastepanov et al. [2013]: soil chambers measurements in Greenland, small CH4 and CO2 flux pulses were detected in spring). To provide a more in-depth understanding of greenhouse gas emissions on the North Slope of Alaska, we employed a multiscale approach in the field and the laboratory. We combined ecosystem-scale measure- ments from two eddy flux towers, local measurements of soil temperature and soil gas concentrations, and a controlled soil-core thawing laboratory experiment. The study allowed us to link the source, mechan- ism, and magnitude of spring pulses of CO2 and CH4 from thawing permafrost tundra on the North Slope of Alaska. 2. Methods 2.1. Field Site Our field site is located near the village of Barrow, Alaska, on the shores of the Beaufort and Chukchi Seas, approximately 400 km north of the Brooks Range. The main research site is operated by the U.S. Department of Energy (DOE) Next Generation Ecosystem Experiment (NGEE) and is located on the Barrow Environmental Observatory (BEO, 71.29°N, 156.61°W). Here, an eddy tower was installed, soil temperature was measured, and the soil cores were taken. The secondary research site is located 4 km to the north and is operated by the U.S. DOE Atmospheric Radiation Measurement Program (ARM, 71.32°N, 156.60°W), where an eddy tower was also erected. The Arctic coastal plain is a relatively flat polygonal tundra. Polygons are geometrical ground features sur- rounded by troughs and formed by growing or decaying ice wedges. The elevation differences between edges and troughs of polygons are roughly 1 m [Hubbard et al., 2012]. The region is underlain by thick con- tinuous permafrost, and the summer active layer is limited to a maximum depth of approximately 50 cm [Gangodagamage et al., 2014]. Mean annual air temperature is À12°C, and mean annual precipitation is 114 mm, with the majority falling as rain during the short summer (1901–2007). Soils in the BEO are highly porous and have high organic content and high water holding capacity [Brown et al., 1980]. The soil can be divided into an organic-rich surface layer 5 to 20 cm thick (depending on location [Hubbard et al., 2012]) underlain by a mineral soil horizon of silty clay to silt loam-textured-mineral material, together comprising the “active layer.” The “permafrost,” a perennially frozen layer, extends from an average depth of 50 cm down to ~600 m [Hubbard et al., 2012].
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