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Improved Constraints on Global Methane Emissions and Sinks Using δ ¹³C-CH₄.

ABSTRACT: We study the drivers behind the global atmospheric methane (CH₄) increase observed after 2006. Candidate emission and sink scenarios are constructed based on proposed hypotheses in the literature. These scenarios are simulated in the TM5 tracer transport model for 1984-2016 to produce three-dimensional fields of CH₄ and δ ¹³C-CH₄, which are compared with observations to test the competing hypotheses in the literature in one common model framework. We find that the fossil fuel (FF) CH₄ emission trend from the Emissions Database for Global Atmospheric Research 4.3.2 inventory does not agree with observed δ ¹³C-CH₄. Increased FF CH₄ emissions are unlikely to be the dominant driver for the post-2006 global CH₄ increase despite the possibility for a small FF emission increase. We also find that a significant decrease in the abundance of hydroxyl radicals (OH) cannot explain the post-2006 global CH₄ increase since it does not track the observed decrease in global mean δ ¹³C-CH₄. Different CH₄ sinks have different fractionation factors for δ ¹³C-CH₄, thus we can investigate the uncertainty introduced by the reaction of CH₄ with tropospheric chlorine (Cl), a CH₄ sink whose abundance, spatial distribution, and temporal changes remain uncertain. Our results show that including or excluding tropospheric Cl as a 13 Tg/year CH₄ sink in our model changes the magnitude of estimated fossil emissions by ∼20%. We also found that by using different wetland emissions based on a static versus a dynamic wetland area map, the partitioning between FF and microbial sources differs by 20 Tg/year, ∼12% of estimated fossil emissions.

SUBMITTER: Lan X

PROVIDER: S-EPMC8244052 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Greenhouse gas (GHG) emissions from Arctic permafrost soils create a positive feedback loop of climate warming and further GHG emissions. Active methane uptake in these soils can reduce the impact of GHG on future Arctic warming potential. Aerobic methane oxidizers are thought to be responsible for this apparent methane sink, though Arctic representatives of these organisms have resisted culturing efforts. Here, we first used in situ gas flux measurements and qPCR to identify relative methane sink hotspots at a high Arctic cytosol site, we then labeled the active microbiome in situ using DNA Stable Isotope Probing (SIP) with heavy 13CH4 (at 100 ppm and 1000 ppm). This was followed by amplicon and metagenome sequencing to identify active organisms involved in CH4 metabolism in these high Arctic cryosols. Sequencing of 13C-labeled pmoA genes demonstrated that type II methanotrophs (Methylocapsa) were overall the dominant active methane oxidizers in these mineral cryosols, while type I methanotrophs (Methylomarinovum) were only detected in the 100 ppm SIP treatment. From the SIP-13C-labeled DNA, we retrieved nine high to intermediate quality metagenome-assembled genomes (MAGs) belonging to the Proteobacteria, Gemmatimonadetes, and Chloroflexi, with three of these MAGs containing genes associated with methanotrophy. A novel Chloroflexi MAG contained a mmoX gene along with other methane oxidation pathway genes, identifying it as a potential uncultured methane oxidizer. This MAG also contained genes for copper import, synthesis of biopolymers, mercury detoxification, and ammonia uptake, indicating that this bacterium is strongly adapted to conditions in active layer permafrost and providing new insights into methane biogeochemical cycling. In addition, Betaproteobacterial MAGs were also identified as potential cross-feeders with methanotrophs in these Arctic cryosols. Overall, in situ SIP labeling combined with metagenomics and genome binning demonstrated to be a useful tool for discovering and characterizing novel organisms related to specific microbial functions or biogeochemical cycles of interest. Our findings reveal a unique and active Arctic cryosol microbial community potentially involved in CH4 cycling.

Dataset Information

Improved Constraints on Global Methane Emissions and Sinks Using δ ¹³C-CH₄.

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OmicsDI is part of the ELIXIR infrastructure

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Dataset Information

Improved Constraints on Global Methane Emissions and Sinks Using δ 13C-CH4.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

Improved Constraints on Global Methane Emissions and Sinks Using δ ¹³C-CH₄.