Accumulation rates of carbon in mires in Finland and implications for climate change

Stratigraphical analyses based on 1028 dated Holocene peat cores were used to estimate the rate of carbon accumulation in Finnish peatlands. Results were compared with data from other Boreal areas. The basal age of peat columns was found to be the best predictor of carbon accumulation and a significant correlation between depth and age of peat was evident. When normalized for the mean depth of peatlands in Finland (c. 1.5 m), the average long-term carbon accumulation was 26.1 g C m(-2) yr(-1). In individual cores the values ranged from 2.8 to 88.6 g (average 22.5 +/- 11.6 g) being much higher in bogs than in fens and almost double in southern mires as compared with those in the northern Boreal zone. The modelled rate of actual carbon accumulation is about 2/3 of that above. Boreal mires are actual sinks of carbon for thousands of years ahead in the present climate. The predicted greenhouse warming may shift the present Sphagnum mires northward and the net effect may be to restrain the radiative forcing. Poorly known 3D mass accumulation in mires and unpredictable functioning of northern mire ecosystems to climatic changes (for example via increased mire fires) complicate this interpretation.