Sensitivity of boreal forest carbon balance to soil thaw

The climate of the boreal zone has warmed significantly in this century and is predicted to warm further in the next century[1]. The seasonally and perennially frozen soils of boreal [...]
We used eddy covariance; gas-exchange chambers; radiocarbon analysis; wood, moss, and soil inventories; and laboratory incubations to measure the carbon balance of a 120-year-old black spruce forest in Manitoba, Canada. The site lost 0.3 ± 0.5 metric ton of carbon per hectare per year (ton C [ha.sup.-1] [year.sup.-1]) from 1994 to 1997, with a gain of 0.6 ± 0.2 ton C [ha.sup.-1] [year.sup.-1] in moss and wood offset by a loss of 0.8 ± 0.5 ton C [ha.sup.-1] [year.sup.-1] from the soil. The soil remained frozen most of the year, and the decomposition of organic matter in the soil increased 10-fold upon thawing. The stability of the soil carbon pool (~150 tons C [ha.sup.-1]) appears sensitive to the depth and duration of thaw, and climatic changes that promote thaw are likely to cause a net efflux of carbon dioxide from the site.