Equations based on empirical relationships of peat physical properties were used to estimate the average long-term apparent rate of carbon accumulation (LORCA) in Finnish mire vegetation regions. The results were generalized to the boreal and subarctic regions. Analyses of 1302 dated peat cores were used to infer carbon accumulation for each mire vegetation region of Finland. The area-weighted LORCA for Finnish undrained mire areas was 18.5 g m 2 yr 1 and the total carbon sink 0.79 Tg yr 1 (1 Tg = 1012g). The total carbon pool of Finnish undrained mires was estimated as 2257 Tg. The aapa-mire region included 80% of the total net accumulation rate of carbon and 85% of the total carbon reservoirs of Finnish undrained mires. LORCA was signi” cantly higher in the raised-bog region, 26.1 g m 2 yr 1, compared with the aapa-mire region, 17.3 g m 2 yr 1, and bogs generally had a higher LORCA 20.8 g m 2 yr 1, than fens 16.9 g m 2 yr 1. The total C sink for boreal and subarctic mires was estimated at 66 Tg yr 1 which is about 31% lower than the previous estimates. The total C pool of all boreal and subarctic mires was estimated at 270–370 Pg (1 Pg = 1015g).

(1) Models of peat accumulation are developed that include constant, linear and quadratic decay of dry mass remaining. Profiles of dry bulk density of 795 peatlands distributed over Finland are used to infer cumulative carbon for each site. These values and basal ages are themselves used to infer rates of growth and decay of the peat. (2) A method, 'function parameter fitting' (FPF), is devised to estimate parameter values in non-linear functions when there are uncertainties in both variables, as there are in cumulative carbon and age. Where the data are highly variable then results with FPF are substantially different from those used hitherto that assume uncertainty in only the dependent variable. (3) For five regions in Finland and in Boreal Canada the inferred rate of addition, p* [M L-2 T-'I, is related to degree-days above zero, and decay, a* [T-'1 is related logarithmically to mean annual temperature. The present day rate of accumulation of carbon in northern peatlands is about 5.6 Tmol yr-' or, as dry mass, 0.07 Gt yr-I. (4) There are difficulties in the interpretation of LARCA (=LORCA = long term average rate of carbon accumulation). Understanding of peatland dynamics may result from the use of intrinsic models allowing decay: it is unlikely to emerge from the exotic models in common use.

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.

[1] Recent and long-term accumulation rates of carbon (C), using 210 Pb-and 14 C-dating, were examined in 23 ombrotrophic peatlands in eastern Canada, where average 1990-1996 atmospheric wet nitrogen (N) deposition ranged from 0.3 to 0.8 g N m À2 yr À1 . The average recent rate of C accumulation (RERCA) over the past 150 years was 73 ± 17 (SD) g C m À2 yr À1 , ranging from 40 to 117 g C m À2 yr À1. The difference in RERCA between hummocks (78 g C m À2 yr À1 ) and hollows (65 g C m À2 yr À1 ) was significant. Increased RERCA over the past 50 years was found in hummocks and hollows in regions of higher N deposition and related to both elevated N deposition and growing degree-days above +5°C. There was a statistically significant positive relationship between N deposition alone and present-day C accumulation in both hummocks and hollows (R 2 = 0.28 and 0.38, respectively). Recent N accumulation was significantly larger in high N deposition regions. The total average aboveground vegetation biomass of hollows and hummocks did not differ significantly with N deposition. However, a significantly larger vascular plant leaf biomass was found in both hollows and hummocks of the high N deposition class than in the low N deposition class (>0.6 and <0.4 g m À2 yr À1, respectively). The average long-term apparent rate of C accumulation (LORCA) at 15 sites was 19 ± 8 (SD) g C m À2 yr À1, with no significant difference due to age of peat inception, latitude, or continentality.