Increasing Diurnal and Seasonal Amplitude of Atmospheric Methane Mole Fraction in Central Siberia between 2010–2021

Siberia's vast wetlands, permafrost, and boreal forests are significant, but their sources of methane (CH4) are poorly quantified. Using vertical CH4 profiles and meteorological data from the ZOtino Tall Tower Observatory (ZOTTO; 60°48′ N, 89°21′ E) in Central Siberia, we analyse long-term trends in CH4 growth rates, seasonal patterns, and diurnal cycles from 2010 to 2021. Our results show a persistent long-term trend in CH4 mole fractions and an insignificant increasing seasonal cycle amplitude, (2.12 ppb year-1, p = 0.12) along with a pronounced late-summer CH4 peak. Diurnal analysis reveals a growing summer CH4 amplitude over the analysed decade (5.55 ppb year-1, p = 0.002), driven by rising nighttime fluxes strongly correlated with soil temperature (R² = 0.7, p < 0.001) and moisture (R² = 0.60, p = 0.031). Notably high nighttime CH4 fluxes occurred in 2012 and 2019 due to wildfires and in 2016, likely due to wetland activity induced by higher temperature. These findings suggest that increasing late-summer CH4 emissions, primarily from wetlands to the west and southwest of ZOTTO, contribute to the overall CH4 rise. Our study underscores the importance of continuous, high-frequency greenhouse gas observations for accurately quantifying regional CH4 trends.