The timing of snow melt controls the annual CO2 balance in a subarctic fen

Abstract

The first continuous multi‐year measurements of the CO₂ exchange between a subarctic fen and the atmosphere were conducted at Kaamanen in northern Finland (69°N). According to our six‐year data‐set, the fen is presently a sink of atmospheric CO₂ with a mean rate of −22 g C m⁻² yr⁻¹. The interannual variation of the CO₂ balances originates almost completely from the variations during the snow‐free period, but the efflux in the wintertime constitutes a significant part of the annual balance. The snow melt timing is the most important single determinant of the annual carbon balance. In contrast to a commonly‐held view, the hydrometeorological conditions during the growing season had only a minor effect on the annual balance, emphasizing the importance of year‐round measurements. This study indicates that climate warming may increase the length of the growing season and thus benefit rather than threaten the carbon pool of subarctic peatlands.