Integrating methane isotopic source signatures with high-resolution wetland fluxes to interpret atmospheric δ13C–CH4 measurements in the central Amazon

The decreasing global trend in δ¹³C–CH₄ suggests that rising biogenic sources are a plausible explanation for the accelerated atmospheric mole fraction observed over the last decade. Tropical wetlands play a critical role in this context and represent one of the largest sources of uncertainty in the global methane budget. The Amazon lowland region, where up to 20–30% of the area can be seasonally flooded, is among the largest natural methane sources in the tropics. However, limitations in both isotopic observations and the representation of wetland diversity and sparse ground base flux measurements continue to limit our ability to attribute emissions to specific ecosystem types and to understand their temporal variability.

In this study, we combine new methane isotopic source signature information from different wetland and aquatic environments in central Amazonia with a refined wetland flux map for the lowland Amazon basin. The combined isotopic and bottom-up flux information is used in atmospheric transport simulations to interpret methane mole fractions and δ¹³C–CH₄ time series at the Amazon Tall Tower Observatory (ATTO). Using a tagged-tracer approach we explore the ability of habitat-specific methane source signatures to distinguish wetland contributions to atmospheric δ¹³C–CH₄ measurements compared to anthropogenic and fire sources. Our results contribute to improving measurement-based source attribution and to reducing uncertainties in regional methane budgets for tropical wetlands.