When wet Arctic tundra soils begin to freeze in the fall, an unfrozen layer remains between the frozen surface and deeper permafrost layers. This period is known as the zero curtain, as liquid water keeps the temperature of this soil layer near 0 Celsius (C) while latent heat is gradually dissipated. This project investigates the methanogenic Archaea that are metabolically active in the unfrozen layer during the fall zero curtain period and compares this community to that which is active in the late summer at the same depth (10-20 centimeters (cm)). This dataset contains the abundance of distinct partial mcrA (Methyl-coenzyme M reductase alpha subunit) gene sequences (operational taxonomic units, OTU's defined at 16% similarity) amplified from messenger ribonucleic acid (mRNA) extracted from soil samples in this study. These data complement the sequences deposited in GenBank (accession numbers OL505703-OL505708).
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Methane production in laboratory incubations of Arctic soil at three temperatures, 2018
When wet Arctic tundra soils begin to freeze in the fall, an unfrozen layer remains between the frozen surface and deeper permafrost layers. This period is known as the zero curtain, as liquid water keeps the temperature of this soil layer near 0 Celsius (C) while latent heat is gradually dissipated. This experiment compares the temperature response of the methanogenic community in the zero curtain period with that of the summer community to test whether the zero curtain methanogenic community is especially cold adapted. This dataset includes methane production rates measured in anaerobic laboratory incubations of soils collected from two dates (July and Nov 2018) at temperatures around 0, 4 and 10C.
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- Award ID(s):
- 1702797
- NSF-PAR ID:
- 10310649
- Publisher / Repository:
- NSF Arctic Data Center
- Date Published:
- Subject(s) / Keyword(s):
- ["Q10","zero curtain","methanogenesis","tundra"]
- Format(s):
- Medium: X Other: text/xml
- Sponsoring Org:
- National Science Foundation
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When wet Arctic tundra soils begin to freeze in the fall, an unfrozen layer remains between the frozen surface and deeper permafrost layers. This period is known as the zero curtain, as liquid water keeps the temperature of this soil layer near 0 Celsius (C) while latent heat is gradually dissipated. This project investigates the microbes that are metabolically active in the unfrozen layer during the fall zero curtain period and compares this community to that which is active in the late summer at the same depth (10-20 centimeters (cm)). This dataset contains the abundance and taxonomic designation of distinct 16S ribosomal ribonucleic acid (16S rRNA) sequences (operational taxonomic units, OTU's) associated with samples in this study. These data complement the sequences and metadata deposited in GenBank Bioproject PRJNA780202.more » « less
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When wet Arctic tundra soils begin to freeze in the fall, an unfrozen layer remains between the frozen surface and deeper permafrost layers. This period is known as the zero curtain, as liquid water keeps the temperature of this soil layer near 0 Celsius (C) while latent heat is gradually dissipated. Significant methane emissions have been observed during this period but the role of concurrent biological production vs escape of stored methane requires more study. This dataset includes dissolved methane concentrations from the active layer (upper 35 centimeters (cm)) of Arctic tundra soils during the fall zero curtain period and in the spring, at the beginning of the thaw period. These data help address the question of biological methane production and storage during the fall.more » « less
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Abstract An estimated 1700 Pg of carbon is frozen in the Arctic permafrost and the fate of this carbon is unclear because of the complex interaction of biophysical, ecological and biogeochemical processes that govern the Arctic carbon budget. Two key processes determining the region’s long-term carbon budget are: (a) carbon uptake through increased plant growth, and (b) carbon release through increased heterotrophic respiration (HR) due to warmer soils. Previous predictions for how these two opposing carbon fluxes may change in the future have varied greatly, indicating that improved understanding of these processes and their feedbacks is critical for advancing our predictive ability for the fate of Arctic peatlands. In this study, we implement and analyze a vertically-resolved model of peatland soil carbon into a cohort-based terrestrial biosphere model to improve our understanding of how on-going changes in climate are altering the Arctic carbon budget. A key feature of the formulation is that accumulation of peat within the soil column modifies its texture, hydraulic conductivity, and thermal conductivity, which, in turn influences resulting rates of HR within the soil column. Analysis of the model at three eddy covariance tower sites in the Alaskan tundra shows that the vertically-resolved soil column formulation accurately captures the zero-curtain phenomenon, in which the temperature of soil layers remain at or near 0 °C during fall freezeback due to the release of latent heat, is critical to capturing observed patterns of wintertime respiration. We find that significant declines in net ecosystem productivity (NEP) occur starting in 2013 and that these declines are driven by increased HR arising from increased precipitation and warming. Sensitivity analyses indicate that the cumulative NEP over the decade responds strongly to the estimated soil carbon stock and more weakly to vegetation abundance at the beginning of the simulation.
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Abstract The atmospheric methane (CH4) concentration, a potent greenhouse gas, is on the rise once again, making it critical to understand the controls on CH4emissions. In Arctic tundra ecosystems, a substantial part of the CH4budget originates from the cold season, particularly during the “zero curtain” (ZC), when soil remains unfrozen around 0 °C. Due to the sparse data available at this time, the controls on cold season CH4emissions are poorly understood. This study investigates the relationship between the fall ZC and CH4emissions using long‐term soil temperature measurements and CH4fluxes from four eddy covariance (EC) towers in northern Alaska. To identify the large‐scale implication of the EC results, we investigated the temporal change of terrestrial CH4enhancements from the National Oceanic and Atmospheric Administration monitoring station in Utqiaġvik, AK, from 2001 to 2017 and their association with the ZC. We found that the ZC is extending later into winter (2.6 ± 0.5 days/year from 2001 to 2017) and that terrestrial fall CH4enhancements are correlated with later soil freezing (0.79 ± 0.18‐ppb CH4day−1unfrozen soil). ZC conditions were associated with consistently higher CH4fluxes than after soil freezing across all EC towers during the measuring period (2013–2017). Unfrozen soil persisted after air temperature was well below 0 °C suggesting that air temperature has poor predictive power on CH4fluxes relative to soil temperature. These results imply that later soil freezing can increase CH4loss and that soil temperature should be used to model CH4emissions during the fall.
