Published online by Cambridge University Press: 08 November 2017
We present a radiocarbon (14C) dataset of tropospheric air CO2, forest soil air CO2, and soil CO2 emissions over the course of one growing season in a Scots pine forest in southern Finland. The CO2 collection for 14C accelerator mass spectrometry (AMS) analysis was done with a portable, suitcase-sized system, using molecular sieve cartridges to selectively trap CO2. The piloting measurements aimed to quantify the spatial, seasonal and diurnal changes in the 14C content of CO2 in a northern forest site. The atmospheric samples collected above the canopy showed a large seasonal variation and an 11‰ difference between day and nighttime profiles in August. The higher Δ14C values during night are partly explained by a higher contribution of 14C-elevated soil CO2, accumulating in the nocturnal boundary layer when vertical mixing is weak. We observed significant seasonal trends in Δ14C-CO2 at different soil depths that reflected changes in the shares of autotrophic and heterotrophic respiration. Also the observed diurnal variation in the Δ14C values in soil CO2 highlighted the changes in the origin of CO2, with root activity decreasing more for the night than decomposition.