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AUXILIARY MATERIAL
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Text S1
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Table S1 summarizes the results of 14C dating, with the properties of samples
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submitted for 14C dating, un-calibrated and calibrated 14C ages and laboratory number.
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Figures S1–S3 summarize the gross stratigraphy (with 14C Cal yrs BP) measured
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values for physical properties of samples and geochemical variables that are
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considered proxies for degradation or humification. The variables δ15N, δ13C, A600/C
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and HA C/N are expected to increase with decomposition or humification while the
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opposite is true for bulk C/N, HA H/C, E4/E6, and ∆log K (see section 4.1 for
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discussion). For easier interpretation, all the x-axes scales in figures S1-S3 are drawn
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so that a shift to the right corresponds to increased degradation or humification. The
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low LOI values at 950° C indicate that soils in the study area contain low amounts of
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carbonates (0.77 ±0.39 %, data not shown). In some sites differentiation between the
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B and C horizon was not possible in the field and the symbol B/C is used.
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1.1. SE1, Shrub Tundra / Folic Stagnic Cambisol (Gelic)
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The soil at SE1 has developed a 15 cm thick folic O-horizon followed by a 7 cm thick
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A-horizon which overlies a silty loam B/C soil horizon (figure S1A). Despite being
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quite thick, 14C-dating shows that the base of the O-horizon consists of young SOM
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(55 or 11 cal yrs BP). The upper O-horizon is rich in Sphagnum litter, has low dry
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bulk density (DBD) and very high C/N ratio. The C/N ratio shows a marked decrease
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with depth. There is enrichment of δ15N with depth in the upper 30 cm and then it
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stabilizes. Notably, here is a very small enrichment of δ13C throughout the profile.
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The degree of humification (E4/E6, A600/C and ∆log K) increases with depth in the O
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and A-horizons, but decreases below ≈45 cm in the B/C- horizon. The C/N ratio in
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HA shows a decrease in the upper 35 cm and then increases. The recovery of FA/HA
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increases from <10% in the upper soil to >40% in the B/C-horizons.
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1.2. SE2, Dwarf Birch Tundra / Gelistagnic Cambisol
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The soil at SE2 has developed a 6 cm thick O-horizon followed by a weakly colored
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A-horizon, which overlies silty loam B/C horizons (figure S1B). The O-horizon in
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SE2 is relatively thin (6 cm) and mainly composed of fluffy moss litter. There is no
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horizons of similar composition have modern basal ages, Table S1). There is a gradual
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decrease of bulk C/N with depth, which is mirrored by enrichment of δ13C and δ15N.
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A600/C is very low throughout the core, whereas ∆log K and E4/E6 are high in upper
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part, but decrease rapidly below 30 cm. The HA C/N ratio is between 8 to 15
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throughout the core, whereas the H/C ratio is very high and increases with depth.
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Recovery of FA/HA increases beneath the O-horizon and remains relatively stable
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between 20-30% in the mineral soil horizons.
C-date from this interval, but it is assumed to be young (upland sites with thicker O-
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1.3. SE3, Spruce Forest / Haplic Podsol
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The soil at SE3 has the most well-developed soil horizons in this study. A 10 cm thick
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O-horizon overlies the well-developed silty sandy loam A and B- horizons (figure
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S1C). The SOM in the upper A-horizon is young SOM (9–12 cm, 55 cal yrs BP).
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There is a slight decrease of bulk C/N with depth up to the C-horizon. δ15N is
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enriched from the O- to A-horizon, then decreases slightly with depth. There is
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gradual enrichment of δ13C down-core to the C-horizon, where there is a marked
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increase (possibly caused by inorganic C not fully removed in the acid cleaning
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process). All three humification analogues indicate a very high degree of humification
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in the transition from A to B-horizon. The HA C/N ratio shows some variability, but
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remains relatively low (<20); the H/C ratio of HAs increases with depth below the A-
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horizon. Recovery of FA and HA is high, 40% to 60%, in the B and B/C-horizons.
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1.4. SE4, Tundra Fen / Cryic Fibric Histosol
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In SE4, there is a 41 cm thick peat deposit overlying a buried permafrost A-horizon
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overlying B/C-horizons (figure S2A). Vascular plant (rootlet) peat started to
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accumulate at this site around 3800 cal yrs BP. Around 1300 cal yrs BP there was a
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shift to a Sphagnum dominated plant community, which is still present today. The
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bulk C/N ratio is very high (>60) in the upper Sphagnum peat, below which the ratio
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remains stable around ≈25 in the rootlet peat and in the mineral permafrost subsoil.
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There is a slight enrichment of δ15N with depth, whereas δ13C remains stable
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throughout the profile. The A600/C is low and stable throughout the core. Both Δlog K
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and E4/E6 decreases in the buried permafrost layers (which suggest a higher degree of
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humification in this older strata, indicating a possible pre-existing mineral soil that was
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buried due to paludification). The C/N and H/C ratios of HAs are low and consistent.
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There is an increase of FA/HA recovery in the mineral sub-soil.
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1.5. SE5, Fen, Plateau Margin / Fibric Histosol
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The peat deposit at this site along the plateau margin is ≈120 cm thick (figure S2B).
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Between 60 and 120 cm depth, the deposit consists of graminoid dominated fen peat
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(SOM age 2450 cal yrs BP at 80-85 cm depth). Above 60 cm depth and up to the
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surface, there is Sphagnum dominated peat, which began accumulating around 1300
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cal yrs BP. No samples are available from the mineral sub-soil for this site. The C/N
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ratio is very high (50 to 100) in the upper Sphagnum dominated peat. In the graminoid
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dominated fen peat below this horizon the C/N ratio is constant around 15. There is
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some variability, but no clear trend in 15N values; 13C shows a slight decrease with
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depth. A600/C decreases with depth, whereas ∆log K and E4/E6 increases with depth.
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Data for elemental composition of HAs is lacking in the upper part of the core, but the
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deeper samples show very low and consistent C/N and H/C ratios. The recovery of
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FA/HA is up to 20 % in the top 10 cm, but is ≤ 10 % throughout the peat deposit.
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1.6. SE6, Fen in Plateau / Fibric Histosol (Gelic)
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In SE6, a 108 cm deep peat deposit overlies a thin A-horizon followed by silty loam
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B/C-horizons (figure S2C); the permafrost table is at 121 cm depth. From 63 to 108
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cm depth there is a deposit of fen peat rich in wood remains, which started to
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accumulate around 3300 cal yrs BP; at 63 cm depth (dated to 1050 cal yrs BP) there is
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a shift to Sphagnum dominated peat formation. Above this thin (10 cm) Sphagnum
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layer there is a layer of fen peat, which is again followed by a thin layer of Sphagnum
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peat near the surface. The upper Sphagnum layer has a high bulk C/N ratio below
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which the ratio remains stable (≈ 20), down to the peat/mineral contact. δ 15N is
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enriched in the upper 40 cm then decreases and remains stable (≈ 0‰), in the deeper
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peat to decrease sharply just above the permafrost surface. δ13C is relatively stable
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around -25‰ to -28‰. A600/C is low in all samples, but increases at the interface
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between peat and mineral sub-soil. Both ∆log K and E4/E6 are highly variable in the
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upper 40 cm, but remain low and stable into the mineral sub-soil. The C/N ratio in HA
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increases with depth, whereas H/C shows a decrease. The recovery of FA/HA is 15-20
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% in the surface peat and ≈40 % in the mineral subsoil, but very low (< 5%) in the
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peat samples between 40 and 110 cm.
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1.7. SE7, Peaty Tundra in Plateau / Folic Fibric Cryosol
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SE7 is located in the uplifted permafrost plateau. There is 29 cm rootlet peat overlying
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a thin A-horizon and a silty loam B/C-horizons (figure S3A). The permafrost table is
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at 55 cm depth in the C-horizon. The SOM at the base of the rootlet peat is 5100 cal
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yrs BP old. There is some variability of bulk density in the permafrost probably
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caused by a variability of ground-ice content. There is little variability in the bulk C/N
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ratio which gradually decreases from ≈20 to ≈10 with depth. The bulk H/C ratio is
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stable in the peat but increases substantially in the mineral sub-soil and in the
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permafrost. There is a slight enrichment of δ 15N from 1 ‰ to 7 ‰ in the mineral sub-
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soil and δ 13C is stable at -26 ‰ in the peat, but is slightly enriched with depth to -24
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‰ in the mineral soil. A600/C is low and decreases further in the upper permafrost
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where ∆log K decreases in a similar pattern while FA recovery increases and HA
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recovery decreases. C/N ratio for HAs is lacking for the permafrost samples (N % was
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below detection). There is little variability in the H/C ratio of HAs with depth.
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1.8. SE8, Peat Plateau / Folic Cryic Histosol
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The peat deposit in SE8 is 410 cm thick (figure S3B). It started to accumulate as early
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as ≈7700 cal yrs BP. The gross stratigraphy indicates little variability in the botanical
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composition of the first 350 cm of peat which appear to consist of graminoid
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dominated fen peat. There is a Sphagnum dominated peat layer between 46 and 55 cm
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followed by a layer of rootlet peat at the surface. The bulk elemental ratios are
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invariant throughout the core with a clear divergence in C/N to ≈50 in the Sphagnum
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peat. δ 15N is enriched in the upper meter of peat (5 to 8‰), but is consistently around
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0‰ to -1‰ in the deeper peat into the mineral sub-soil where it increases to 3‰. δ
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C is slightly enriched in the upper 100 cm but remains constant around -27‰. The
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C/N and H/C ratios of HAs are relatively low and remain mostly unchanged with
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depth. The recovery of FA/HA is between 5% to 13% in the peat and increases to
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17% in the mineral soil.
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1.9. SE9, Peat Plateau / Folic Cryic Histosol
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The second peat plateau deposit at site SE9 is somewhat thinner and younger than
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SE8; it is 325 cm deep with a basal age ≈7200 cal yrs BP (figure S3C). The peat
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stratigraphy is similar to SE9, the main exception is the presence of woody layers
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between 100-150 cm. Except for a slight increase to 30 in the Sphagnum dominated
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layer, the bulk C/N ratio is around 20 or lower throughout the peat deposit. The bulk
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H/C ratio in the peat does not change in the upper 300 cm depth, but increases in the
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mineral sub-soil. δ 15N is 2 to 3‰ in the upper rootlet peat and then varies between -
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0.55‰ to 1.7‰ in the peat down to the peat/mineral interface where there is further
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enrichment to 5 ‰. δ 13C varies between 24‰ and 30‰ throughout the peat including
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the mineral soil. The peat deposit shows very little variability with low humification
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and low C/N and H/C ratios in HAs. There is however a marked increase in
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humification at the peat/mineral contact. The recovery of FA/HA is < 5% in most of
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the core, but is >10 % in the near surface Sphagnum dominated peat and in the
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mineral sub-soil.
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Table S1. Results of radiocarbon dating, with site name, depth intervals, soil/land cover and sample
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descriptions, 14C and cal BP ages, as well as sample laboratory numbers.
Site
Depth
Soil / Vegetation. Sample description
Age 14C BP/ PMC
Age cal BPa
Lab. no.b
Upland tundra sites
N.Ac
14-16 cm
Folic Cambisol / Shrub tundra. Base of O-hor.
112.37 ±0.36 PMC
14
Poz-35117
N.Ac
28-30 cm
Folic Gleyic Cambisol / Shrub tundra. Base of O-hor.
103.12 ±0.33 PMC
53
Poz-35119
N.Ac
22-30 cm
Folic Cambisol / Spruce forest. A/B-horiz.
109.42 ±0.35 PMC
10
Poz-28229
SE1
13-14 cm
Folic Stagnic Cambisol / Shrub tundra. Base of O-hor.
108.40 ±0.36 PMC
52 (9)
Poz-35120
SE3
9-12 cm
Haplic Podsol / Spruce forest. Upper A-hor.
104.31 ±0.34 PMC
53
Poz-35116
Fen peat deposits
SE4
24-25 cm
Cryic Fibric Histosol / Tundra fen. Base of Sph. peat
1280 ±35
1300
Poz-28280
SE4
38-39 cm
Cryic Fibric Histosol / Tundra fen. Basal peat
3520 ±35
3830
Poz-28251
SE5
55-60 cm
Fibric Histosol / Fen, plateau margin. Base of Sph. .peat
1290 ±30
1305
Poz-28250
SE5
80-85 cm
Fibric Histosol / Fen, plateau margin. Fen peat
2380 ±35
2465
Poz-28316
SE6
63-67 cm
Fibric Histosol / Fen in plateau. Base of Sph. peat
1120 ±30
1075
Poz-28238
SE6
106-108
Fibric Histosol / Fen in plateau. Basal peat
3025 ±35
3295
Poz-28239
104.60 ±0.36 PMC
55
Poz-28277
Plateau bog peat deposits
SE7/8/9d
5-10 cm
Folic Cryic Histosol / Bog peat plateau. Rootlet peat
SE7
29-30 cm
Folic Fibric Cryosol / Peaty tundra in plateau. Basal peat
4435 ±35
5070
Poz-35121
SE8
185-190 cm
Folic Cryic Histosol / Bog peat plateau. Fen peat
5290 ±40
6115
Poz-28241
SE8
405-408 cm
Folic Cryic Histosol / Bog peat plateau. Basal peat
6790 ±40
7700
Poz-28242
SE9
27-35 cm
Folic Cryic Histosol / Bog peat plateau. Sphagnum peat
935 ±30
890
Poz-28244
SE9
40-50 cm
Folic Cryic Histosol / Bog peat plateau. Fen peat
2225 ±35
2400
Poz-36630
SE9
154-164 cm
Folic Cryic Histosol / Bog peat plateau. Woody fen peat
4835 ±35
5655
Poz-28245
SE9
331-336 cm
Folic Cryic Histosol / Bog peat plateau. Basal peat
6200 ±50
7170
Poz-28246
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a.
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2008, calibrated using OxCal 3 and OxCal 4 (PMC dates only). For SE1, the older of the two possible
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dates was used for the regression analyses b. Laboratory number at Poznan Radiocarbon Laboratory. c.
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Samples from soil horizons in upland tundra sites not analyzed further in this study. d. Dated sample is
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from a peat plateau site 100 m SE of SE7.
Indicated age is the highest probability interval median expressed as calendar years before
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ONLINE SUPPL: FIGURES CAPTIONS
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Figure S1. SOM characteristics in tundra and forest soils. X-axes show: 1- bulk organic C content
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(TOC ), 2 - dry bulk density (DBD), 3-4 - stable isotope composition of organic N and C (δ15N and
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δ13C), 5- C/N ratio of bulk soil, 6-8 - humification of HAs (E4/E6, A600/C and ∆ log K), 9-10 - C/N and
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H/C ratios of HAs, 11 – bulk soil TOC storage, 12 - recovery of FA/HA in the extraction process. Y-
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axes shows depth and diagram to the right shows the general stratigraphy with soil horizons,
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dominating grain size fractions and permafrost.
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Figure S2. SOM characteristics in fens. X-axes show: 1- total organic C content (TOC), 2 - dry bulk
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density (DBD), 3-4 - stable isotope composition of organic N and C (δ15N and δ13C), 5- C/N ratio of
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bulk soil, 6-8 - humification of HAs (E4/E6, A600/C and ∆ log K), 9-10 - C/N and H/C ratios of HAs, 11
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– bulk soil TOC storage, 12 – recovery of FA/HA in the extraction process. Y-axes shows depth and
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diagram to the right shows the gross stratigraphy with botanical composition of peat (Root peat =
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rootlet peat dominated by black roots, Sph. peat= Sphagnum dominated peat, Fen peat =graminoid
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dominated fen peat, woody= >10 % wood), soil horizons, dominating grain size fractions and
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permafrost.
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Figure S3. SOM characteristics in permafrost peat plateaus. X-axes show: 1- total organic C content
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(TOC), 2 - dry bulk density (DBD), 3-4 - stable isotope composition of organic N and C (δ15N and
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δ13C), 5-6 - C/N and H/C ratio of bulk soil, 7-8 - degree of humification in humic acids (A600/C and ∆
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log K), 9-10 - C/N and H/C ratios of HAs, 11- bulk soil TOC storage, 12 - recovery of FA/HA in the
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extraction process. Y-axes shows depth and diagram to the right shows the gross stratigraphy with
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botanical composition of peat (Root peat = rootlet peat dominated by black roots, Sph. peat= Sphagnum
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dominated peat, Fen peat =graminoid dominated fen peat, woody= >10 % wood) and soil horizons,
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dominating grain size fractions and permafrost.
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