Journal of Nuclear and Radiochemical Sciences, Vol. 9, No. 2, pp. 41-44, 2008

Relationship between Carbon-14 Concentrations in Tree-ring Cellulose and Atmospheric
CO2
Yoshimune Yamada,*,a Kaeko Yasuike,a and Kazuhisa Komurabab

Faculty of Pharmaceutical Sciences, Hokuriku University, Kanagawa-machi, Kanazawa-City 920-1181, Japan
Low Level Radioactivity Laboratory, Kanazawa University, Tatsunokuchi-machi, Nomi-City 923-1224, Japan

Received: June 19, 2008; In Final Form: Sptember 1, 2008

Concentrations of organically-bound 14C in the tree-ring cellulose of a Japanese Cedar (Cryptomeria japonica) grown in a rural region of Kanazawa, Ishikawa prefecture, Japan (36.5°N, 136.7°E), were measured forthe ring-years from 1989 to 1998 to study relationship between 14C concentrations in tree-ring cellulose andatmospheric CO2 in a narrow region. An interesting result in comparing our data of tree-ring cellulose withthose of atmospheric CO2 is that the 14C concentration in tree-ring cellulose was close to the corresponding
average from mid-June to early September of 14C concentrations in atmospheric CO2. Furthermore, the 14C
concentrations in tree-ring cellulose were found to be merely influenced by the drastic decrease of 14C concentrations in atmospheric CO2 in winter, which might be caused by air pollution from the Asian continent andadditional local fossil fuel contribution. These results suggest that the 14C concentration in tree-ring cellulose
for a given growing year reflects the 14C concentrations of atmospheric CO2 during the warm summer months.

1. Introduction
Most of environmental 14C (half life = 5730 y) originatesfrom continuous production by cosmic rays in the upper atmosphere and from thermonuclear bomb tests carried out during
the 1950s and early 1960s.1-3
It could be estimated that the 14 C records in a series ofannual rings of trees reflect the variations in the levels of 14C
concentration in atmospheric CO 2 at the growth site of thetree.4-16 Carbon necessary for synthesizing a variety of chemical compounds in tree rings is derived essentially from the CO2
in the air by photosynthesis. Measurement of 14C in the cellulose fraction of tree rings is a preferred method for the analysisof annual variations in 14C concentrations, since organicallybound carbon in the cellulose undergoes no changes following
the time of tree-ring formation. However, there has been little
literature referring to the relationship between 14C concentrations in tree-ring cellulose and atmospheric CO2 in a narrow
region up to date.7-9
In our previous paper,17 temporal variation of 14C concentrations in atmospheric CO2 samples collected every 10 days wasmeasured in the Ohkuwa area of Kanazawa, Ishikawa prefecture, Japan (36.5°N, 136.7°E), where local contamination fromfossil-fuel combustion can be disregarded, during the period
from April 1991 to December 2000 to estimate the backgroundlevel of environmental 14 C and to clarify the influence of air
containing a large amount of 14 C-free fossil fuel CO2 transported across the Sea of Japan from the Asian continent on thelevels of environmental 14C. The Ohkuwa area is located in thelowlands about 40 m above sea level in a rural region southeast
out of the center of the city. There are no factories releasing alarge amount of 14 C-free fossil fuel CO2 in the surroundingarea. Thereafter, the same method was applied to the samples
collected in the Takao area of Kanazawa (36.5°N, 136.6°E),
which is located in an urban area near the center of the city,and then, levels of 14C in atmospheric CO2 in urban area werecompared with background levels of 14C in atmospheric CO2 to*Corresponding author. E-mail: yo-yamada@hokuriku-u.ac.jp,
FAX: +81-76-229-2781

estimate the local fossil fuel contribution to 14C concentrationsin atmospheric CO2.18
In the present study, the concentration of organically-bound14
C in the tree-ring cellulose of a Japanese Cedar (Cryptomeria
japonica) grown at a site located about 1.6 km southeast of thesampling site of atmospheric CO2 samples in the Ohkuwa areaof Kanazawa was measured for the ring-years from 1989 to
1998 to study relationship between 14C concentrations in treering cellulose and atmospheric CO2.

2. Experimental
2.1. Cellulose samples of tree rings. The trunk of a 54year-old Japanese Cedar (Cryptomeria japonica), 0.48 m indiameter, and 0.7 m in length, was cut at the position of 0.5–1.2
m above the ground surface on October 18, 1998, and was analyzed in the present study. The tree was grown at a site on the
top of a small hill in the Tachi area of Kanazawa, Ishikawa
prefecture, Japan (36.5°N, 136.7°E), as shown in Figure 1. The
growing site of the tree in the Tachi area was located about 1.6
km southeast of the sampling site of atmospheric CO2 in theprevious study, which was in a rice field of 1 km 2 in the
Ohkuwa area.17 There are no factories releasing large amountsof 14C-free fossil fuel CO2 in the surrounding area.
Each cellulose fraction corresponding to the 1989–1998
ring-years was isolated from wood chips according to the same
method that was applied to a 67-year-old pine tree (JapaneseBlack Pine; Pinus thunbergii) grown in Shika-machi, Ishikawa
prefecture, Japan (37.0°N, 136.8°E) in our previous study.15
2.2. Combustion of cellulose samples. The cellulose fraction of 100 g corresponding to a single year was gently burned
to obtain the combustion water for tritium measurement andCO2 for 14C measurement.15,19 The carbon dioxide gas was collected as a dry-ice form, and the resulting dry-ice was immediately converted to calcium carbonate. Approximately 280 g ofdried CaCO3 obtained from 100 g of cellulose was stored in an
airtight vessel.
2.3. Benzene synthesis for the preparation of 14C counting sources. The original CO2 was regenerated by adding asolution of perchloric acid dropwise to 40 g of the stored© 2008 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 12/05/2008

42

YamadaJ. Nucl. Radiochem. Sci., Vol. 9, No. 2, 2008

TABLE 1: Carbon-14 concentration in tree-ring celluloseof a Japanese Cedar (Cryptomeria japonica) in Kanazawa,
Ishikwa prefecture, Japan (36.5 °N,136.7 °E)
∆14C*
(‰)

Year
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989

101.0
107.5
113.3
123.6
138.7
138.4
154.1
140.5
159.4
171.1

±
±
±
±
±
±
±
±
±
±

δ13C
(‰)
4.6
4.8
4.6
4.8
4.4
6.0
4.5
4.3
4.8
5.2

-24.36-24.07-23.68-23.65-23.46-23.39-22.96-23.13-23.93-23.77*The error denotes a counting error of 1σ.
All samples were measured using a low background liquid
scintillation counter, Aloka LB-1.

Figure 1. Sampling sites of the tree and the atmospheric CO2 samples for 14 C measurement, Kanazawa, Ishikawa prefecture, Japan(36.5°N, 136.7°E).
Fine lines in the figure represent rivers in Ishikawa prefecture, Japan.

CaCO3. It was then converted to benzene in a vacuum by themethod described previously.15
The counting source for a liquid scintillation spectrometer
was prepared by adding a toluene based butyl-PBD scintillation
solution to 3.5–4.0 g of synthesized benzene to a total volumeof 20 mL. The synthesized benzene prepared from NIST
oxalic acid (SRM 4990C) was used as a standard reference of
14C.
2.4. Measurement of 14C. The 14C activity was measured
by a low background liquid scintillation counter, Aloka LB-1,
under temperature-stabilized conditions at 12 °C at least for
100 min x 40 times. The counting background of the 20 mL
low potassium glass vial was 2.64 cpm at a rate of 58% efficiency. The results are presented as ∆14 C, as defined in ourprevious paper.10 Isotopic fluctuation of a sample was correctedusing the δ13C value determined by a Finnigan-MAT DeltaPLUS
Stable Isotope Ratio Mass Spectrometer.
3. Results and Discussion
The concentration of organically-bound 14C in the tree-ringcellulose of a Japanese Cedar grown in a rural region of
Kanazawa, Ishikawa prefecture, Japan (36.5°N, 136.7°E), wasmeasured for the ring-years from 1989 to 1998 to study relationship between 14C concentrations in tree-ring cellulose andatmospheric CO2 . The growing site of the tree was locatedabout 1.6 km southeast of the sampling site of atmospheric CO2
samples in the Ohkuwa area, in which temporal variation of
14
C concentrations in the atmospheric CO2 samples collected
every 10 days was measured during the period from April 1991
to December 2000.17

The results of measurement for the tree expressed as the∆14C value are given in Table 1. The ∆14C values in the table,
after corrections for isotopic fluctuation using δ13C and radioactive decay of 14 C, were reproducible at ±10‰ or less, as
described previously.10
The relationship between the ∆14C and the ring year of theJapanese Cedar for the ring-years from 1991 to 1995 is illustrated by bar graphs in Figure 2. The temporal variation of∆14C values in atmospheric CO2 every 10 days is also illustrated
in the figure. In addition, annual averages and averages from
mid-June to early September of the ∆14C values in atmospheric
CO2 are plotted in the figure, respectively.
The most important result in this study is that the ∆14C value
in tree-ring cellulose of the Japanese Cedar demonstrated elevated levels higher than the corresponding annual average of∆14C values in atmospheric CO2. Furthermore, the ∆14C value
in tree-ring cellulose was close to the corresponding average
between mid-June and early September of the ∆14 C values inatmospheric CO2, although a significant difference appeared in
1994.
In the previous paper,17 it was revealed that the ∆14C values
in atmospheric CO2 in the Ohkuwa area, where local contamination from fossil-fuel combustion can be disregarded,decreased gradually by about 5‰ each year from 1991 to 2000,
with a pronounced seasonal cycle which began to increase fromspring and reached the maximum in late July or early August,followed by a decrease to the minimum from December to
February. The appearance of the extreme decrease of the ∆14C
value in winter seemed to be caused by the influence of air
containing a large amount of 14 C-free fossil fuel CO2 transported across the Sea of Japan from the Asian continent.
Furthermore, it was also revealed that the monthly mean levelsof 14C concentration in the Takao area demonstrated 10–50‰
lower concentrations than the background levels only in thewinter season.18 This additional decrease seemed to be causedby the local fossil fuel contribution by heating in the winterseason in the Takao area, which is located in an urban region
near the center of Kanazawa.
However, the present data for the tree demonstrated that the
air pollution from the Asian continent and additional local fossil fuel contribution in winter merely affected the ∆14C values
in tree-ring cellulose. The unexpected result mentioned above
suggests that the tree-ring cellulose was scarcely synthesized
in winter, since the carbon necessary for synthesizing cellulose
seems to be supplied essentially by photosynthesis from theRelationship between Carbon-14 Concentrations in Tree-ring Cellulose

J. Nucl. Radiochem. Sci., Vol. 9, No. 2, 2008

43

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Figure 2. Relationship between ∆14C values in tree-ring cellulose and atmospheric CO2 in Kanazawa, Ishikawa prefecture, Japan.
The bar graph (dark gray): Japanese Cedar (Cryptomeria japonica) in the Tachi area (36.5°N, 136.7°E) in this study.
Gray line: The atmospheric CO2 in the Ohkuwa area (36.5°N, 136.7°E).17
Black line: The atmospheric CO2 in the Takao area (36.5°N, 136.6°E).18
Annual average of the atmospheric CO2:
The Ohkuwa area,
The Takao area.
The average from mid-June to early September for atmospheric CO2:
The Ohkuwa area, The Takao area.

CO2 in the air.
In comparing 14C concentrations in tree rings with those of
atmospheric CO2 , it is of importance that a subject when thecellulose in a certain part of tree ring was synthesized from theCO2 in the air. There have been several literatures concerning
this subject.5,7-9
Levin and Kromer 9 reported that the tree-ring data closely
match the summer values of the air samples averaged over themonths May to August by the analysis of individual tree rings(Picea abies) collected in the vicinity of Schauinsland station(48°N, 8°E) located close to the top of Schauinsland Mountainin the Black Forest, southern Germany, at an elevation of 1205
m asl.
Nakamura et al.5 reported that early wood of each annual
ring for a Kiso hinoki tree (Chamaecyparis obtusa, Japanesecypress) grown in a rural forest, Gifu prefecture, Japan, wasformed from the beginning of May to the end of July by assuming an equal growth rate. They also reported that the variations in the ∆14C values of the early wood of individual annual
rings for the Kiso hinoki from 1958 to 1966 showed good
agreement with those of atmospheric CO2 in Spain from 1962
to 1963 and in Norway from 1963 to 1966. On the basis ofthese observations, they explained that the time-lag between
the fixation of CO2 by the tree through photosynthesis and thecellulose formation of the tree using the photosynthetic products seems to be negligible during the growing season of thetree. Similar results were reported by Olsson and Possnert8that the total growing time was normally from June to the endof August for an oak tree grown in a suburb of Uppsala in
Sweden, and there was no clear evidence for any delay in 14C
activity between the atmospheric CO2 in Abisko in northern
Sweden and the cellulose fraction in the tree on a time scale ofweeks. However, it should be noted that there have been conflicting reports concerning this subject. Grootes et al.7 reported
that ∆14C values of tree ring cellulose seem to follow those of
atmospheric CO2 with a delay of 5 to 6 weeks.

It is apparent from these considerations that the 14C concentration in tree-ring cellulose for a given growing year indicatesthe 14C concentration of atmospheric CO2 during the growing
season of the tree. The difference of the indicated intervals of
growth of tree rings within one month among several trees
grown in distinct areas in the northern hemisphere seemed tobe mainly caused by the climatic conditions, since the formation of boundaries of tree rings can be influenced easily byexternal factors, such as the climate of the place where thesample tree grew.20
The relationship between the ∆14C and the ring year of theJapanese Cedar for the ring-years from 1991 to 1999 is illustrated by bar graphs in Figure 3 together with those of the pinetree (Japanese Black Pine; Pinus thunbergii) from Shika-machi(37.0°N, 136.8°E), Ishikawa prefecture, Japan, revealed in theprevious paper.15
The comparison of ∆14C values in tree-ring cellulose for thetwo sets of trees collected at different regions of Ishikawa prefecture indicated that annual variation of ∆14C values in treering cellulose of the Kanazawa-sample in this study had
essentially similar variations to that of the Shika-sample andsignificant difference was not observed in the ∆14 C values
between the two sets of samples.
From these results, it was found that there was no local variation of the 14C concentration in atmospheric CO2 between two
different regions of Ishikawa prefecture, and that the ∆14C values in tree-ring cellulose of the Shika-sample for a given growing yea r might ref lect averages of the ∆ 14 C values ofatmospheric CO2 from mid-June to early September. It is noteworthy that significant difference of the ∆14 C value derived
from the difference of species of tree was not observed between
the Japanese Cedar and the Japanese Black Pine.
4. Conclusion
The concentration of organically-bound 14C in the tree-ring44

YamadaJ. Nucl. Radiochem. Sci., Vol. 9, No. 2, 2008

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Figure 3. The relationship between the ∆14C and the ring year of the Japanese Cedar (Cryptomeria japonica) for the ring-years from 1991 to1999 together with those of the Japanese Black Pine (Pinus thunbergii) from Shika-machi (37.0°N, 136.8°E), Ishikawa prefecture, Japan.
The bar graph (dark gray): Japanese Cedar (Cryptomeria japonica) in the Tachi area of Kanazawa (36.5°N, 136.7°E) in this study.
The bar graph (light gray): Japanese Black Pine (Pinus thunbergii) in Shika-machi (37.0°N, 136.8°E).15
Gray line: The atmospheric CO2 in the Ohkuwa area of Kanazawa (36.5°N, 136.7°E).17
Black line: The atmospheric CO2 in the Takao area of Kanazawa (36.5°N, 136.6°E).18
Annual average of the atmospheric CO2:
The Ohkuwa area,
The Takao area.
The average from mid-June to early September for atmospheric CO2:
The Ohkuwa area, The Takao area.

cellulose of a Japanese Cedar grown in a rural region of
Kanazawa, Ishikawa prefecture, Japan (36.5°N, 136.7°E), wasmeasured for the ring-years from 1989 to 1998 to study relationship between 14C concentrations in tree-ring cellulose andatmospheric CO2.
The ∆14C values in tree-ring cellulose demonstrated elevatedlevels higher than the corresponding annul average of ∆14C values in atmospheric CO2 , and was close to the corresponding
average of the ∆14C values in atmospheric CO2 from mid-Juneto early September. Furthermore, the ∆14C values in tree-ringcellulose was found to be merely influenced by the drastic
decrease in ∆14 C values in atmospheric CO2 in winter, whichmight be caused by the air pollution from the Asian continent.
These observations suggest that a large part of the carbon necessary for synthesizing tree-ring cellulose seems to be derived
from the atmospheric CO2 during the growing season of thetree.
On the basis of these results, it is concluded that the ∆14 C
values in tree-ring cellulose for a given growing year mightreflect the average of ∆14 C values in atmospheric CO2 from
mid-June to early September.
Acknowledgments. The authors wish to express their thanks
to Dr. Hikaru Amano, Japan Atomic Energy Agency, and Ms.
Miwako Yamamichi, Japan Marine Science Foundation, fortheir helpful advice in our mass spectrometry analyses.
This study was supported in part by a Grant from the
Ish i kawa P refe ct u ra l I nst it ute of P ubl ic Hea lt h a nd
Environmental Science.
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