Abstract
Unprecedented warming of Arctic–boreal regions (ABR) has poorly
understood consequences on carbon cycle processes. Uncertainties in
annual methane (CH4) budgets partly arise because of limited data
availability during winter. In this study, winter CH4 flux measurements
were conducted using the snowpack diffusion gradient method over five
ABR ecosystem types in Canada and Finland: closed–crown and open–crown
coniferous boreal forest, boreal wetland and erect–shrub and
prostrate–shrub tundra. Boreal forest uplands acted as net CH4 sinks,
while the boreal wetland acted as net CH4 source during winter. We
identified several wetland tundra CH4 emission hotspots and large
spatial variability in boreal wetland CH4 emissions. In the boreal
forest uplands, soil liquid water content was identified as an important
environmental control of winter CH4 fluxes. Our results indicate
non–negligible winter CH4 flux, which must be accounted for in annual
carbon balance and terrestrial biosphere models over ABR.