Soil Organic Carbon:
Quantity and Distribution in Arctic Tundra Soils
Associated with the ATLAS Winter C-Flux Study
G.J. Michaelson1, and C.L. Ping1
1
University of Alaska Fairbanks, Agric. and Forestry Exp. Stn.
Palmer Res. Center, Palmer, Alaska, 533 E. Fireweed, Palmer, AK 99645.
Introduction
Research is underway to develop and improve models that describe the exchange of carbon from arctic ecosystems.
Recent measurements of carbon flux have indicated that wintertime flux of CO2 from the arctic tundra region can
be a very significant part of the seasonal fluxes, up to 60% (Oechel et al., 1997). Models often use total OC stocks
of the surface soil layers, mostly surface organic layers, to represent the pool available for biological activity. This
is to represent the system as it functions in the warm season. However during the cold-season, soil OC stocks
down to the permafrost are often at nearly the same temperatures (0 to –10oC) for an extended period of time up to
8 months. This seasonal temperature shift presents a challenge with respect to assessing the quantity and quality of
soil OC that may be important to soil respiration at low temperature. It is likely that there is a very substantial
change in both the quantity and quality of SOC available to microbes during this cold period. Soil OC stocks down
to 50 or even 100 cm depth could play a more significant role in total soil respiration. Due to the subzero
temperatures, soil OC dissolved or with the potential to be dissolved in the soils unfrozen water could become the
most significant substrate for microbes. The result of this could be that the total OC stocks of the surface organic
layer may not be the best indicators of OC available for wintertime respiration or for indicators in predictive
models that assess year round activity.
Objective
Determine the quantity of soil OC and soil water-soluble OC (OCws) and their distribution in soil profiles at the
ATLAS Winter C-Flux Study sites along the western Alaska transect.
Materials and Methods
Sampling
The soils of each study site (Fig. 1) were examined and described in the field according to Soil Survey Manual
(Soil Survey Division Staff, 1993). Soil samples were taken from the major soil genetic horizons that were
exposed in the walls of pits excavated on each ATLAS Study site (approx. 1 m3). Samples were taken to the
Palmer Soils for analysis.
Laboratory
Soil bulk density was determined on dimensional samples taken in the field-weighed in the lab. Total OC was
determined by LECO CHN analyzer, water soluble OC (OCws) by equilibration of soil with water (1.45:10 v/v) for
12 hrs at 25oC and C-stores for site profiles calculated by the method of Michaelson et al., (2001).
Results
Barrow
Atqasuk
Flux Tower
Total
OC
Walker Plot
Oi
Oa
10
Oumalik Sites
Nonacidic Tundra
Oi Oa
Oi
Oe
10
10
Bw
20
Bw/Bg
cm
O/A
30
40
Oajj/2Cg
50
60
80
Cgf1
Oa
30
Bg
70
1
1.5
70
39 kgOC m-3
80
71 kgOC m-3
Bgf
90
100
0.5
Oa/Bgjj
60
80
Cgf2
Oa
90
100
50
Bgf
70
38 kgOC m-3
28 kgOC m-3
90
40
60
80
0
30
50
60
2Cgf
20
40
Bw
50
70
Oa
20
Bg/Oa
Ab
40
Oi/O
e
10
Bg/Oajj
20
30
Acidic Tundra
90
100
0
0.5
1
1.5
100
0
-1-1
0.5
1
1.5
0
0.5
1
1.5
kgOC
kgOCm
m-2-2cm
cm
Water
Soluble
OC
c
10
10
10
10
20
20
20
20
30
30
30
30
40
40
40
40
50
50
50
50
60
60
60
60
70
70
70
21 gOCws m-3
80
40 gOCws m-3
80
90
80
90
100
1
2
3
4
5
90
100
0
1
2
3
4
5
48 gOCws m-3
80
90
100
0
70
33 gOCws m-3
100
0
gOC
gOCws
m-2-2cm
cm-1-1
wsm
1
2
3
4
5
0
1
2
3
4
5
Ivotuk Sites
Tussock Tundra (1)
Shrub
TussockTundra
Tundra(Tower)
(Tower)
Tussock
Oi
Oi
10
Oi
10
Oe
20
Nonacidic Tundra
10
1010
Oe/Oa
20
20
OiOi
2020
Oe
Oe
Oa
30
30
30
3030
40
40
40
4040
Bw
Bw
Bg
cm 50
50
50
5050
60
60
60
6060
70
Bg/Oaf
80
70
70
51 kgOC m-3
Bg
Bg
38 kgOC m-3
7070
62 kgOC m-3
Cf
BgOaf
BgOaf
80
80
8080
90
90
9090
104kgOC
kgOCm
m-3-3
104
Cgf
Cgf
90
100
100
100
0
0.5
1
1.5
0
0.5
1
100
100
0
1.5
-2
kgOC m cm
cm
0.5
1
1.5
-1
00
10
10
10
1010
20
20
20
2020
30
30
30
3030
40
40
40
40
40
50
50
50
50
50
60
60
60
60
60
70
70
33 gOCws m-3
80
58 gOCws m
80
90
1
2
3
4
5
1
2
3
4
5
100
100
0
-2
1.5
1.5
90
90
100
0
11
109gOC
gOCwsm
m-3-3
109
ws
80
80
90
100
0
35 gOCws m-3
80
90
100
70
70
70
-3
0.5
0.5
gOCws m cm
1
-1
2
3
4
5
0
0
1
1
2
2
3
3
4
4
5
5
Council Sites
Open Shrub (Blueberry Hill)
Tundra
Open Woodland
Woodland
Open
Shrub
Oi
Oi
Oi/Oa
10
10
Oi
10
Oi
20
20
30
30
20
20
20
30
30
30
30
40
40
40
40
50
BC
50 BC
50
50
60
60
60
60
Bw
Bw
40
BC
50
50
60
Bg
60
58 kgOC m-3
BCg
70
70
Oab
80
80
90
100
Oa
Bw
Bg/Cg
cm
Oi
10
Bhs
Bhs
20
A
Oa1/Oa2
Oa
Oa
10
10
A
Oa
40
Forest
70
28 kgOC m-3
2Bwb
Bsh
70
70
15 kgOC m-3
70
19 kgOC
kgOC m
m-3-3
19
BC2
BC2
80
80
80
80
90
90
90
90
90
100
100
100
100
100
38 kgOC m-3
2C
2Cr
0
0.5
1
0
1.5
0.5
1
0
1.5
0.5
1
-1
-2
1.5
00
0.5
0.5
11
0
1.5
1.5
0.5
1
1.5
kgOC m cm
10
10
10
10
10
10
20
20
20
20
20
20
30
30
30
30
30
30
40
40
40
40
40
40
50
50
50
50
50
50
60
60
60
60
60
60
cm
70
70
70
125 gOCws m-3
80
48 gOCws m-3
80
90
90
100
1
2
3
4
5
80
80
80
90
90
90
100
100
0
70
70
58 gOCws m-3
0
1
2
3
4
5
70
51 gOC
gOCws
m-3-3
51
ws m
90
100
100
0
1
2
3
gOCws m-2 cm-1
4
5
83 gOCws m-3
80
100
00
11
22
33
44
55
0
1
2
3
4
5
Quartz Creek Sites
Tussock Tundra
Inter Stripe
Lichen Stripe
Oi
Oe/A1
Oe/Oi
Oi/Oe
A2/Bw1
10
10
10
A/Bw1
Bw2
Bw/A
20
20
20
30
30
30
40
40
40
cm 50
50
50
60
60
60
70
70
70
39 kgOC m
80
100
80
80
90
90
100
0.5
1
12 kgOC m-3
6 kgOC m-3
-3
90
0
A/Bw2
A3/Bw3
Bw/Oaj
j
1.5
100
0
0.5
1
-1
-2
1.5
0
0.5
1
1.5
kgOC m cm
cm
10
10
10
20
20
20
30
30
30
40
40
40
50
50
50
60
60
60
70
70
35 gOCws m-3
80
80
90
90
100
70
80
90
100
0
1
2
3
4
5
66 gOCws m-3
13 gOCws m-3
100
0
1
2
3
gOCws m-2 cm-1
4
5
0
1
2
3
4
5
Quantity and distribution of soil OC
Soil profile distribution of OC for each site is presented in the top row of Figure 2. Carbon stores were generally
within the range of stores found for the Kuparuk River Basin soils (Michaelson et al., 1996). The Ivotuk tussock
tundra tower site had the highest stores at 104 kgOC m-3 followed by the more northern Oumalik acidic tundra site,
the nonacidic tundra site at Ivotuk and the Council tundra site at 71, 62 and 58 kgOC m-3 respectively. Soil profiles
at these sites contained relatively high amounts of OC compared with other study sites, largely due to the effects of
cryoturbation. This was evident from the substantial portions of the OC stores found at depth in the combination
(O/B or B/O) and Cf horizons. Similarly at the Quartz Creek sites the tussock tundra contained large proportions
of its stocks in the Bw/O horizon with total stocks similar to those found at the other tundra sites. Soils under the
lichen stripes at Quartz Creek contain OC stocks similar to the alpine soils of the Kuparuk Basin and only slightly
lower than shrub sites at Council. Study sites at Council contained varying amounts of OC ranging from high to
low in the order of tundra (w/permafrost), forest, open shrub, open woodland, and shrub sites at 58, 38, 28, 19 and
15 kgOC m-3 respectively. High tundra stocks were as mentioned above due to cryoturbation. Forest stocks were
largely in the Oa (well decomposed organic) and Bsh (containing illuvial organic matter). Stocks of the open shrub
site were a large part due to the mixing/burying effects of slope movement processes as evidenced by the
substantial stocks found at depth in the profile. The open woodland profile mirrors that of the forest but with
smaller amounts of OC. The shrub site also had a distribution pattern similar to the open shrub and forest but with
shallower depth and lower stock levels.
Quantity and distribution of water soluble OC
It can be presumed that at low temperatures, biological activity and therefore respiration should be highly
dependent on liquid water and the organic substrates that may be available in it. Therefore soil profile stocks of
water-soluble organic carbon (OCws) were determined for each site and the data are presented in the lower part of
Figure 2. Two points are most apparent in these data: (1) there is a quantity variation among profiles, and a range
in distribution of OCws relative to the amount of total OC in the profiles, and (2) the ratio for stocks of OCws:OC is
not the same between study areas.
(1) In general, the largest soil profile OCws stocks were found in the Council tundra and the Ivotuk tussock (tower)
sites. However these sites were highest due to the large amounts of OCws stocks in the upper permafrost horizons.
Vegetation types such as mature forest, lichens and shrubs apparently serve to elevate the OCws stocks found in a
profile when compared to tussock tundra sites. The quantity of OCws was not necessarily related to the amount of
total OC in a profile.
(2) There is quite a wide range of ratios for profile OCws: OC (gOCws m-3: kgOC m-3) stocks among soils at
different locations. Sites with a significant presence of shrubs had the highest proportions of OC ws . The highest
ratios or proportions of OCws were in the Quartz Creek inter stripe (high in shrubs at 5.5), Council shrub (3.9) and
open woodland (2.7), Council forest and tundra (2.2), Quartz Creek lichen (2.2), Council open shrub (1.7), and
Ivotuk shrub (1.5). Tussock tundra sites all had ratios between 0.6 and 1.0.
Conclusions
1. Organic C stocks of ATLAS study sites were similar in quantity and distribution to comparable sites in the
Kuparuk River Basin of the central Alaska Arctic. The presence of mixed mineral/organic horizons at depth due to
cryoturbation, significantly elevate OC stocks.
2. Water-soluble OC stocks are elevated in soils under forest, lichen and shrub vegetation relative to tussock
tundra. The quantity of OCws was not necessarily related to the amount of total OC in a soil profile.
References
Michaelson, G.J., C.L. Ping, and J.M. Kimble, Carbon storage and distribution in tundra soils of Arctic Alaska,
U.S.A., Arctic and Alpine Res. 28(4), 414-424, 1996.
Michaelson, G.J., C.L. Ping, and J.M. Kimble, Effects of soil morphological and physical properties on estimation
of carbon storage in arctic soils, in Lal et al., (eds) Assessment Methods For Soil Carbon, Ch. 23, p339-348, CRC
Press, 2001.
Oechel, W.C., G. Vourlitis , and S.J. Hastings, Cold-season CO2 emissions from arctic soils. Global Biogeoch.
Cycles 11:163-172, 1997.
Soil Survey Division Staff, Soil Survey Manual, USDA Handbook No. 18. U.S. Government Printing Office,
Washington, D.C., 1993.