TIME-INTEGRATED COLLECTION OF CO 2 FOR 14 C ANALYSIS FROM SOILS

We developed a passive sampler for time-integrated collection and radiocarbon ( 14 C) analysis of soil respiration, a major flux in the global C cycle. It consists of a permanent access well that controls the CO 2 uptake rate and an exchangeable molecular sieve CO 2 trap. We tested how access well dimensions and environmental conditions affect collected CO 2 , and optimized cleaning procedures to minimize 14 CO 2 memory. We also deployed two generations of the sampler in Arctic tundra for up to two years, collecting CO 2 over periods of 3 days–2 months, while monitoring soil temperature, volumetric water content, and CO 2 concentration. The sampler collects CO 2 at a rate proportional to the length of a silicone tubing inlet (7–26 µg CO 2 -C day -1 ·m Si -1 ). With constant sampler dimensions in the field, CO 2 recovery is best explained by soil temperature. We retrieved 0.1–5.3 mg C from the 1st and 0.6–13 mg C from the 2nd generation samplers, equivalent to uptake rates of 2–215 ( n= 17) and 10–247 µg CO 2 -C day -1 ( n= 20), respectively. The method blank is 8 ± 6 µg C (mean ± sd, n= 8), with a radiocarbon content (fraction modern) ranging from 0.5875–0.6013 ( n= 2). The sampler enables more continuous investigations of soil C emission sources and is suitable for Arctic environments.