Increasing Methane Summer Diurnal Amplitude in Siberia: A 2010–2021 Analysis from the ZOtino Tall Tower Observatory (ZOTTO)

Siberia’s extensive wetlands, permafrost, and boreal forests are significant sources of methane, positioning this region as crucial for global methane (CH₄) monitoring. However, Siberia remains sparsely monitored by atmospheric and ecosystem observatories, highlighting the need to leverage existing datasets to refine CH₄ budgets with better spatial and temporal precision. Utilising the ZOtino Tall Tower Observatory (ZOTTO; 60°48' N, 89°21' E) dataset, which provides continuous, high-resolution CH₄ mole fraction and meteorological measurements from six heights up to 301 meters, combined with ERA5 meteorological data at 60°75' N, 89°25' E, we conducted a comprehensive analysis of long-term trends and variations in atmospheric CH₄ at ZOTTO, examining its diurnal and seasonal patterns from 2010 to 2021. Our analysis reveals a significant increase in the summer diurnal amplitude of CH₄, which could be driven by both forest and meteorological dynamics, through the effects of daytime mixing and nighttime stability on the CH₄ mole fraction, and ecosystem CH₄ flux. We found that while atmospheric dynamics showed no significant trends contributing to this diurnal amplitude increase, there was an increasing trend in nighttime CH₄ ecosystem flux in summer (predominantly August) over the 11-year period, with high emissions predominantly originating from the west and southwest of the station. Additionally, episodic high methane CH₄ was observed in 2012 and 2019, linked to wildfires, and in 2016, attributed to enhanced wetland activity. Lastly, there were significant positive correlations between the calculated CH₄ surface flux and soil temperature and moisture at ZOTTO.