Fig. 1 - Coring of wetland active layer and permafrost during July 2010
The Impact of Global Warming on the Carbon Cycle of Arctic Permafrost: An Experimental and Field Based Study
T.C. Onstott, S. Myneni, B. Stackhouse, Princeton Univ.
S.M. Pfiffner , T. Vishnivetskaya and A. Layton, Univ. of Tennessee
L.G. Whyte , N. Mykytczuk, J. Allan, R.C. Wilhem, McGill Univ.
R. Hettich , K. Chourey, and T.J. Phelps, ORNL
S. Elliott and M.F. Kidd, LANL
P. Hatcher, Old Dominion Univ.
1. Perform ~2 years long, heating experiments on well-characterized, intact cores of Arctic active-layer and permafrost from a proposed reference ecosystem site where CO2, N2O and CH4 fluxes, temperatures, humidity, soil moisture, nutrients, microbial diversity and activities and isotopic analyses are currently being measured in the field.
2. Perform phylogenetic, metagenomic, transcriptomics and proteomic analyses of the intact cores.
3. Characterize the abundance and composition of the solid and dissolved organic matter and the inorganic geochemistry in the active layer and permafrost.
4. Characterize changes in the organic matter composition, the vertical flux of volatile organic acids, O2, H2, CO2 and CH4 the isotopic systematics of CO2 and CH4 and changes in the transcriptomics, proteomics and C cycle networks in these cores during the long term heating experiments as the permafrost thaws under water saturated and water under saturated conditions.
5. Compare the results from intact cores and the heating experiments with field measurements.
6. Based upon these heating experiments and field measurements construct a 1D biogeochemical reaction/transport model that predicts the CO2 and CH4 release into the atmosphere as permafrost thaws and compare these predictions with observations at the reference ecosystem site.
Permafrost, or perennially frozen ground, underlies ~24% of the Earth’s surface and contains ~1/3 of the global soil organic C. It is, therefore, a possible source of extremely potent greenhouse gases, such as CH4, N2O and CO2. Temperatures in the Arctic may increase 4-8°C over the next 100 years, thereby increasing the depth of the active-layer and thawing the underlying permafrost. Field observations and ice core records suggest that with thawing, the relatively undegraded permafrost organic C will be rapidly metabolized, creating a positive feedback to global warming through increased CH4, N2O and CO2 emissions. Although many researchers have measured CO2 and CH4 fluxes and characterized the microbial diversity of the Siberian and Canadian active-layer and permafrost, the relationship between methanogenic, methanotrophic and heterotrophic in situ activities within the active-layer and CO2 and CH4 fluxes as a function of temperature has not been delineated either in field or lab experiments. Defining these relationships is essential for determining the extent and rate of this positive feedback in order for these processes to be accurately reflected in global climate models.
To address this paucity of data we will collect 30 intact cores for long term heating experiments from the active layer and permafrost (0-1 meters below surface) at the McGill Arctic Research Station (MARS) on Axel Heiberg Island in the Canadian high Arctic. This site has been the location of climate investigations for the past 50 years. The extensive Arctic wetland area adjacent to the lake at this site will be the source of the intact cores (Fig. 1 top). CO2 flux measurements indicate higher emissions during peak summer months compared to spring time when the ground is completely frozen. The microbial community of the active layer and associated permafrost varies as a function of depth with aerobic phyla dominant near the surface and anaerobic phyla dominant at greater depths. Archaeal phyla, including methanogens, comprise 0.1% of the microbial community. A low diversity fungal component is also present in the active layer and permafrost. Pore water geochemical results also indicate decreasing O2 availability as a function of depth and proximity to the lake. The total organic carbon concentration is uniform with depth, but the dissolved organic carbon varies dramatically with depth with values as high as 100 mm. Aerobic viable cell counts from the active layer are also 100 times those of the permafrost. Anaerobic incubation experiments utilizing organic carbon amendments detect enhanced production of CO2 and CH4 with increasing temperature up to 15oC, relative to undetectable CO2 and CH4 production at 0oC.
Based upon last summer’s coring campaign a new coring bit has been manufactured that will enable the collection of 1-meter long intact cores within polycarbonate tubes that can be sealed and frozen on site (Fig. 1 bottom). Heating experiments will be performed on these tubes in the lab where the temperature, precipitation and humidity of the headspace will be controlled and the gaseous, aqueous and solid phase constituents analyzed over time. Experiments will be performed under both water-saturated conditions and partially saturated conditions that reflect the observed variations in the water table depth of the site. The ongoing incubation experiments will be utilized to design the timing of sacrificial core analyses and the type of organic substrates that will be added in a subset of the cores. Organic and inorganic geochemical, metagenomic, metatranscriptomic and proteomic profiles will be performed on the core samples prior to and during prolonged heating to address questions of nutrient fluxes, diversity, abundance, activity and spatial relationships between microorganisms, respectively. A high sensitivity 14C RNA isotope microarray will be developed based upon the observed 16S rRNA community structure that will map the carbon trophic cascade as permafrost with 14C labeled compounds thaws. Cavity ring down spectrometers will be used to monitor C, O and H isotopic analyses of CH4 and CO2 from the heated cores, from cores amended with 13C labeled compounds and from permafrost emissions at the MARS field site.