We used two datasets of 14C analyses of
archived soil samples to study carbon turnover in
O horizons from spruce dominated old-growth stands
on well-drained podzols in Scandinavia. The main
data set was obtained from archived samples from
the National Forest Soil Inventory in Sweden and
represents a climatic gradient in temperature. Composite
samples from 1966, 1972, 1983 and 2000 from
four different regions in a latitude gradient ranging
from 57 to 67N were analysed for 14C content.
Along this gradient the C stock in the O horizon
ranges from 2.1 kg m-2 in the north to 3.7 kg m-2
in the southwest. The other data set contains 14C analyses from 1986, 1987, 1991, 1996 and 2004 from
the O horizons in Birkenes, Norway. Mean residence
times (MRT) were calculated using a two compartment
model, with a litter decomposition compartment
using mass loss data from the literature for the threefirst
years of decomposition and a humus decomposition
compartment with a fitted constant turnover
rate. We hypothesized that the climatic gradient
would result in different C turnover in different parts
of the country between northern and southern Sweden.
The use of archived soil samples was very
valuable for constraining the MRT calculations,
which showed that there were differences between
the regions. Longest MRT was found in the northernmost
region (41 years), with decreasing residence
times through the middle (36 years) and central
Sweden (28 years), then again increasing in the
southwestern region (40 years). The size of the soil
organic carbon (SOC) pool in the O horizon was
mainly related to differences in litter input and to a
lesser degree to MRT. Because N deposition leads
both to larger litter input and to longer MRT, we
suggest that N deposition contributes significantly to
the latitudinal SOC gradient in Scandinavia, with
approximately twice as much SOC in the O horizon
in the south compared to the north. The data from
Birkenes was in good agreement with the Swedish
dataset with MRT estimated to 34 years
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