TY - JOUR A1 - Galera, Leonardo de A. A1 - Eckhardt, Tim A1 - Beer, Christian A1 - Pfeiffer, Eva‐Maria A1 - Knoblauch, Christian T1 - Ratio of In Situ CO2 to CH4 Production and Its Environmental Controls in Polygonal Tundra Soils of Samoylov Island, Northeastern Siberia Y1 - 2023-04-04 VL - 128 IS - 4 JF - Journal of Geophysical Research: Biogeosciences DO - 10.1029/2022JG006956 PB - N2 - Arctic warming causes permafrost thaw and accelerates microbial decomposition of soil organic matter (SOM) to carbon dioxide (CO₂) and methane (CH₄). The determining factors for the ratio between CO₂ and CH₄ formation are still not well understood due to scarce in situ measurements, particularly in remote Arctic regions. We quantified the CO₂:CH₄ ratios of SOM decomposition in wet and dry tundra soils by using CO₂ fluxes from clipped plots and in situ CH₄ fluxes from vegetated plots. At the water‐saturated site, CO₂:CH₄ ratios decreased sharply from 95 at beginning of July to about 10 in August and September with a median of 12.2 (7.70–17.1; 25%–75% quartiles) over the whole vegetation period. When considering CH₄ oxidation, estimated to reduce in situ CH₄ fluxes by 10%–31%, even lower CO₂:CH₄ ratios were calculated (median 10.9–8.41). Active layer depth and soil temperature were the main factors controlling these ratios. Methane production was associated with subsoil (40 cm) temperature, while heterotrophic respiration was related to topsoil (5 cm) temperatures. As expected, CO₂:CH₄ ratios were substantially higher at the dry site (median 373, 292–500, 25%–75% quartiles). Both tundra types lost carbon preferentially in form of CO₂, and CH₄‐C represented only 0.27% of the dry tundra total carbon loss and 6.91% of the wet tundra total carbon loss. The current study demonstrates the dynamic of in situ CO₂:CH₄ ratios from SOM decomposition and will help improve simulations of future CO₂ and CH₄ fluxes from thawing tundra soils. N2 - Plain Language Summary: Global warming causes the thaw of the permanently frozen soil in Arctic regions, exposing soil organic matter (SOM) previously frozen to decomposition, increasing the emission of carbon dioxide (CO₂) and methane (CH₄), which are greenhouse gases. It is crucial to quantify the ratio of CO₂ and CH₄ produced because CH₄ has a stronger global warming potential than CO₂. We partitioned SOM decomposition into CO₂ and CH₄ formation (CO₂:CH₄ ratios) in wet and dry tundra soils on Samoylov Island, Northeastern Siberia, and we related these ratios to environmental variables. Deeper active layer, which is the topsoil layer that freezes and thaws annually, and higher subsoil (40 cm) temperature at the interface between the active layer and the permafrost, foster CH4 production and decrease CO₂:CH₄ ratios. Carbon was preferentially lost in form of CO₂ by the soils, but CH₄ had a larger contribution to the carbon loss in the wet tundra. Our study indicates that warming and deepening of the active layer can result in rising CH₄ production. Further understanding of in situ CO₂:CH₄ ratios from SOM decomposition will help improve simulations on future CO₂ and CH₄ fluxes from thawing tundra soils. N2 - Key Points: Topsoil (5 cm) warming increases the CO₂:CH₄ production ratio, while warming of subsoil (40 cm) leads to lower CO₂:CH₄ production ratios. The CO₂:CH₄ production ratio is associated with active‐layer depth (ALD) due to a direct effect of ALD on CH₄ production. Carbon was preferentially lost in form of CO₂ at wet and dry sites, but CH₄ had a higher contribution at the wet tundra site. UR - http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/11515 ER -