Stable carbon isotope emission patterns from high latitude landcover types: a synthesis of in-situ δ13C-CH4 and δ13C-CO2 from northern wetlands, lakes, and seasonally-inundated ecosystems

Wetlands, lakes, and seasonally-inundated ecosystems in northern latitudes have high carbon (C) densities and are globally important sources of methane (CH₄ ) and carbon dioxide (CO₂ ) to the atmosphere. Our estimation of these greenhouse gas (GHG) fluxes and their sources, however, remain uncertain and a major challenge for understanding the permafrost C feedback to climate change. Stable carbon isotope signatures (δ¹³ C) inform GHG inventories and potentially reconcile large disagreements that exist between bottom-up and top-down models of the global C budget. They can also be used to establish dominant methanogenic pathways and identify shifts in pathway due to climate forcing.

In an effort to identify isotopic signatures of major GHG emitting landscapes at high latitudes, we compiled numerous in-situ studies measuring δ¹³ C-CH₄ and δ¹³ C-CO₂ from Arctic (>60°N) and boreal ecosystems (>50°N) using the International Soil Radiocarbon Database. Our preliminary results from 20 studies, indicate that mean δ¹³ C-CH₄ (n= 220) and δ¹³ C-CO₂ (n= 1214) from flux and interstitial measurements vary significantly between wetland, lake, and tundra landcover classes (p < 0.0001). We will present an expanded analysis with over 100 studies using land cover classifications from the Boreal-Arctic Wetlands and Lakes Database.

Constraining the ranges of δ¹³ C-CH₄ and δ¹³ C-CO₂ from northern landscapes will improve our understanding of their contribution to the global C cycle and inform modeling of future global climate scenarios. In the future, this synthesis work can be integrated into warming scenarios that predict how hydrologic and land cover changes—driven by rising temperatures, permafrost thaw, and sea level—will impact the global CH₄ and CO₂ budgets. These ranges can also be used to identify landscapes in transition and predict shifts in dominant microbial processes as permafrost thaws. Additionally, this synthesis can be used to compare Arctic and tropical C sources to determine latitudinal trends in isotopic emissions.