desorbed from tree rings of the Siberian stone pine disc, have been obtained. It is shown ..... istry of Natural Resources and Ecology of the Russian. Federation ...
ISSN 10248560, Atmospheric and Oceanic Optics, 2011, Vol. 24, No. 4, pp. 390–395. © Pleiades Publishing, Ltd., 2011. Original Russian Text © B.G. Ageev, A.P. Zotikova, N.L. Padalko, Yu.N. Ponomarev, D.A. Savchuk, V.A. Sapozhnikova, E.V. Chernikov, 2011, published in Optica Atmosfery i Okeana.
OPTICAL INSTRUMENTATION
Variation of H2O, CO2, and CO2 Isotope Composition in Tree Rings of Siberian Stone Pine B. G. Ageeva, A. P. Zotikovab, N. L. Padalkoc, Yu. N. Ponomareva, D. A. Savchukb, V. A. Sapozhnikovaa, E. V. Chernikovc aZuev
Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, pl. Akademika Zueva 1, Tomsk, 634021 Russia b Institute of Monitoring of Climatic and Ecological Systems, Siberian Branch, Russian Academy of Sciences, pr. Akademicheskii 10/3, Tomsk, 634021 Russia cTomsk Branch of Federal State Unitary Enterprise Siberian Research Institute of Geology, Geophysics, and Mineral Resources, Tomsk, pr. Frunze 232, 624021 Russia Received September 15, 2010
Abstract—The experimental measurements of H2O, CO2, and the carbon isotope content of CO2, vacuum desorbed from tree rings of the Siberian stone pine disc, have been obtained. It is shown that: 1) certain cyclic ity exists in annual trends of H2O and CO2; 2) the amplitude of CO2 cycles has markedly risen after 1960; 3) the annual trend of the CO2 concentration in the rings correlates with an increase in atmospheric CO2 con centration; 4) the carbon isotope content varies with the variation of CO2 concentration in a sample. DOI: 10.1134/S1024856011040026
INTRODUCTION An abundance of works is devoted to reconstruc tion of the environment of the past through investiga tion of the ratio of stable isotopes of wood or cellulose. Long series of annual variations of carbon isotopes in wood discs or cores are commonly used as indirect indicators of environment variations: temperature, humidity, local anthropogenic factors, etc., which influenced the balance of the stomatal conductance and photosynthesis rate in the past [1]. The ratios of stable isotopes of oxygen and hydrogen of the wood or cellulose are characteristics of water sources, include the temperature signal and leaf transpiration, which depends on the atmospheric humidity [2]. However, there are large deviations in isotope ratios not only between different trees, but even at the same tree, the cause of which has not been found [2]. We suppose that investigations of desorbed gaseous components of tree discs with the use of a laser photoacoustic spec trometer can partly explain this effect [3–6]. In these works, measurements of CO2 content and its isotope composition in discs of different conifers have shown that the wood of the discs includes the gas component, in which the CO2 concentration and carbon isotope content of CO2 vary from year to year. To conceive of the actual carbon balance in the wood and its isotope ratios, this gas component of the wood, reflecting the annually varying CO2 concentration, should be taken into account. The investigation of water content in discs of living trees is conducted by different methods, for example,
by computer Xray tomography [7]. However, we failed to find works dealing with determination of the annual water content in dry discs. The goal of this work is to determine the annual content of water, CO2, and carbon isotope content of CO2 desorbed from tree rings of discs of the Siberian stone pine (Pinus sibirica Du Tour), as well as to search for climatic response signs in the results. 1. MATERIALS AND METHODS Earlier, we used wood discs with a number of rings no more than 80 in all measurements of CO2 content in tree rings, and the series under study did not exceed 60 rings. In this work, we used a Siberian stone pine disc with a diameter of 66 cm, sawed at a height of 1.5 m, which consisted of 131 rings; the studied series amounted to 100 years. The tree was grown at a Sibe rian stone pine forest of the Trubachevo settlement of the Tomsk region (56°25′ N, 85°06′ E). The disc was held during 6 months in the laboratory condition. This allowed us to consider the disc’s wood material to be room dried. The width of tree rings was measured with an accu racy of 0.01 mm at the disc’s polished surface along two radii on a LINTAB measuring system. The CO2 concentration in gas samples, vacuum extracted from the tree rings, was measured with a laser photoacoustic (PA) spectrometer and the com puterized model of the tunable waveguide CO2 laser [8]. The ultimate absorption coefficient sensitivity of
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the used spectrometer was 2 × 10–5 cm–1 at a laser power of 70 mW, the measurement error did not exceed ± 5%. An additional increase in the sensitivity can be reached at a total gas pressure in the PA detec tor’s cell of 100 Torr; therefore, all experiments were conducted at approximately that pressure.
H2O 1.0 0.9 (U – Uair)/Umax
Before measurements, the PA detector was cali brated, using the CO2/N2 reference mixture, contain ing a known amount of CO2. The wood of rings was planed off with special chisels, then weighed, and put in four sealed exposition chambers, which were pumped out for a short time in order to stimulate gas diffusion [4], and after 20 minutes the measurements started. In all measurements, the gas samples from each exposition chamber (at a pressure of ∼6 Torr) were put into an evacuated PA cell, to which air was added up to a total pressure of ∼100 Torr. Amplitudes of the signals from the analyzed mixture U (air + gas), air Uair and the difference U = U – Uair were recorded automatically. After that, the CO2 concentration in gas samples was determined with the help of the calibrat ing plot. Signals were recorded at four generation lines of the tunable CO2 laser: 10P(20, 16, 14), coinciding with absorption lines of CO2 and 10R(20), coinciding with the absorption line of the H2O vapor. The absorp tion coefficients of H2O at the 10P(20, 16, 14) lines were much less than those of CO2 at these lines [9]; therefore, we assumed that the H2O contribution in the CO2 absorption at the 10P(20, 16, 14) lines was insignificant under our experimental conditions.
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Fig. 1. Temporal variations of signals from components desorbed from a disc at four CO2 laser lines.
The total water content in the tree rings was found by the classical method of drying tree rings up to the perfectly dry state [10]. The milled wood of rings was placed in weighing bottles, which then were put in a thermostat (T ∼ 105–110°C) for 48 h. The water con tent was found from the difference between masses: Х = 100% (b – b1)/b, where b was the mass of the sam ple before drying, b1, the same after drying.
2. EXPERIMENTAL RESULTS 2.1. Temporal Variation of a Signal The rate of the gas desorption from a sample and its possible reciprocal sorption by the wood in exposition chambers has been analyzed preliminarily. To do that, four exposure chambers filled with wood material, approximately homogeneous and equal in mass, were simultaneously subjected to shortterm pumpingout, and during a certain time were under the formed vac uum. Figure 1 presents normalized results of the signal variation with time at different generation lines of the CO2 laser for these four exposure chambers. It is seen that the H2O signal in the shortterm formed vacuum reached its maximum after approxi mately 25 min, and then the resorption began. At the other three lines, where the CO2 signal was recorded, it reached its maximum only after approximately 2.5 h, and then the resorption started again. Values of the CO2 absorption coefficients at the lines of the laser generation are very close; therefore, the CO2 signal spread evidences certain inhomogeneity of the organic wood material in different exposure chambers.
To investigate isotopes, CO2 and H2O were des orbed from a wood ring in the nitrogen stream at T = 80°C. The evolving components were gathered into two traps: H2O, in a cooling trap (T = 4°C), and CO2, in a trap, filled with Ba(OH)2, in which it was depos ited in the form of BaCO3. The stable carbon isotope ratio (δ13C) of CO2 of the wood, as well as ratios of sta ble isotopes of hydrogen and oxygen of water were measured at the accredited Laboratory of Isotopic Methods of Tomsk Branch of FSUE SRIGGMR (cer tificate no. ROSS RU 001.517930) with the help of a DELTA V Advantage mass spectrometer at an error of no higher than ±0.5 and a confidence probability of 0.95.
2.2. Annual Variation of Water Content in a Disc The problem of the annual measurement of water in Siberian stone pine tree rings arose from the fact, noted by us earlier, that there was a correlation between the water and CO2 content variations in discs. The first pilot experiment on the determination of the water content was conducted by the method of total drying of the spruce disc [6]. Results on the annual water content in Siberian stone pine rings, obtained by the classic method of sample drying up to the perfectly dry state, are presented in Fig. 2. Data for 1954 are excluded because of a high content of water, caused by increased resin concentration. The tree rings related to recent years also contain a lot of resin.
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signal amplitudes at the 10R (20) generation line are in most cases higher than at other frequencies, due to a high rate of water diffusion into the exposure chamber. The signal spread at the three generation lines fixing CO2 was caused by the fact that the exposure chambers were connected with the measurement system one after another, which gave time to evolve the additional amount of gas (see Fig. 1). As opposite to the experiment, in which the water amount in tree rings was determined through the total drying during 48 hours up to the perfectly dry state, in the given case we fixed water, evolved during 20 min, i.e., water that easily diffused into the exposure cham ber due to decreasing the pressure (free water). Figure 4 shows that signals from H2O and CO2 have a distinctly noticeable cyclicity (the Fourier analysis has shown the presence of harmonic oscillations with periods of 2, 4, 16.5, 23.5, and 29 years). The annual dynamics of H2O content, found by means of the total drying, and the behavior of H2O signal at the R(20) laser generation line turned out to be different (see Figs. 2 and 4). Evidently, we find the total amount of water (free and bound) at longterm drying. Only free water seemingly was in the PA cell in the experiment with the use of shortterm vacuum. The comparison of data for the Siberian stone pine ring width and annual concentration of CO2, evolved from the tree rings (for the P(20) line), has shown that the increasing content of CO2 falls in the range of the minimal tree ring widths (Fig. 5). In this range (after 1960), a weak correlation between the ring width and CO2 content in it is observed (R = 0.39, P = 0.02009, N = 35); before 1960, a somewhat significant correlation is not observed. Particular time periods are also seen (Fig. 5), where the tree ring width decreased with the CO2 growth (1895– 1905) or increased with its decrease (1940–1950). As it is known, the atmospheric characteristics have changed lately. The CO2 concentration in the atmo sphere has risen and its isotope composition has
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Fig. 2. Variation of water content in Siberian stone pine tree rings.
Trends of fouryearaveraged temperatures for Tomsk during the growing season and of water content in Siberian stone pine since 1890 had the same direc tion (Fig. 3a). It was shown that there existed a weak correlation between water content in the Siberian stone pine disc and summer precipitations during 1896–1960 (R = 0.20; P = 0.10926). One can note a high correlation (R = –0.88, P = 8.69396 × 10–4) between the water content in disc rings and the ring width in the beginning of the tree growth (1883–1896) (Fig. 3b), and a weak one for other years (R = –0.41, P < 0.0001, N = 103). 2.3. Measurement of CO2 and H2O Content in a Disc, Using a Laser Photoacoustic Spectrometer Variations of signals characterizing the CO2 laser radi ation absorption by CO2 and H2O, desorbed from Sibe rian stone pine disc tree rings are presented in Fig. 4. The (a)
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Fig. 5. Annual variation of the tree ring width (1) and CO2 content (2). Measurements are conducted at the P(20) laser line.
changed. Using the table from [2], reflecting the change of atmospheric components (CO2 and ratios of carbon isotopes δ13C), we compared our data with these values (Fig. 6b) through the linear approxima tion of the found data on CO2 content in a Siberian stone pine disc (Fig. 6). A sharp augmentation of the CO2 content in the disc tree rings and a change of the δ13C annual trend concur, while a significant negative correlation is observed between CO2 data and the variation of isoto pic ratio in the atmosphere (R = –0.62, P < 0.0001, ATMOSPHERIC AND OCEANIC OPTICS
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N = 117). The pattern of the annual increase of the CO2 content after 1960 with a maximum in the 1990s has been noted by us earlier for three discs of the same Sibe rian stone pine from the Altai Mountains [4]. Possibly, the augmentation of the CO2 content in disc tree rings is a sign of tree aging, accelerated due to the increased CO2 concentration in the atmosphere and δ13C variations. In our earlier work [6], we have found a correlation between the growth of the atmospheric CO2 and the annual accumulation of CO2 in tree rings of spruce discs. The comparison of data on the annual CO2 vari
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Fig. 6. Annual variation of the CO2 content in the Siberian stone pine disc (a) and atmospheric characteristics (b).
ation in tree rings of the Siberian stone pine disc with data of the Mauna Loa laboratory (2008, http://cdiac. ornl.gov/ftp/trends/co2/maunaloa.co2) also gives a
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–22
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–40 –35 –30 –25 –20 1880 1900 1920 1940 1960 1980 2000 2020 Years Fig. 7. Variation of the carbon isotope composition of CO2 and CO2 content (ppm) in tree rings of the Siberian stone pine disc (a); variation of the isotope composition of the carbon of CO2 in gas samples of the 1920s and 1990s in tree rings of the Siberian stone pine disc (b).
significant value of the correlation coefficient R = +0.63 (P < 0.0001, N = 51) (at the P(20) line). Thus, a con clusion can be drawn that a change of atmospheric properties is reflected in characteristics of gas content in the Siberian stone pine disc. Earlier, we supposed that the studied CO2 is sorbed not only by the wood, but by water as well [6]. The found correlation between growth of CO2 content in Siberian stone pine tree rings and H2O content, deter mined by the total drying method, support this suppo sition (R = 0.55, P = 0.0693, N = 23). 2.4. Variations of the Carbon Isotope Composition of СО2 (δ 13С) Measurements of carbon isotope composition of vacuumdesorbed CO2 have shown that an increase in the CO2 concentration in a sample practically imme diately changes its isotope content (Fig. 7a): the higher the CO2 concentration in a sample, the lighter its iso tope content, and vice versa. The carbon isotope content of CO2 desorbed from the Siberian stone pine tree rings of the 1990s turned out to be much lighter than that of the 1920s (Fig. 7b). This can be partly explained by the fact that the atmo spheric carbon isotope content also became lighter by now as compared to that of the preindustrial atmosphere due to anthropogenic impact: δ13C (1850) = –6.41‰, δ13C (2003) = –8.07‰ [2]. However, basic causes, seemingly, are the age changes of biochemical reac tions and related processes of fractioning of the carbon isotopes [11–15]. We have measured the isotope content of hydrogen and oxygen of water, desorbed from 18 Siberian stone pine tree rings. The isotope content of the hydrogen
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δD varies from –27.3 to –105.2‰; for the oxygen 18O (δ18O), from +1.2 to –22‰, which corresponds to the atmospheric (meteor) nature of water [16].
4. B. G. Ageev, Yu. N. Ponomarev, and V. A. Sapozhnik ova, “Trends of CO2 in Atmosphere and Disc Tree Rings of Conifers,” Izv. Vyssh. Uchebn. Zaved., Fiz. (Tomsk, 2009), p. 16, Dep. v VINITI 30.10.2009, No. 668V2009.
CONCLUSIONS
5. B. G. Ageev, Yu. N. Ponomarev, and V. A. Sapozhnik ova, “Photoacoustic Analysis of CO2 Content in Annual Tree Rings,” J. Appl. Spectrosc. 76, 452–455 (2009).
Longterm series of CO2 and H2O content in discs of Siberian stone pine were obtained experimentally. It has been found that: 1) the annual distributions of CO2 and H2O con centrations are present in Siberian stone pine discs, the cyclicity is observed in these distributions; 2) the accumulation of CO2 in tree rings after 1960 is accompanied by an increase in the cycle amplitude; 3) the observed increase in the CO2 content in tree rings correlates with the growth of atmospheric CO2;
6. B. Ageev, Y. Ponomarev, and V. Sapozhnikova, “Laser Photoacoustic Detection of CO2 in Old Disc Tree Rings,” Sensors 10, 3305–3313 (2010). 7. J. H. Fromm, I. Sautter, D. Matthies, J. Kremer, P. Schumacher, and C. Ganter, “Xylem Water Content and Wood Density in Spruce and Oak Trees Detected by HighResolution Computed Tomography,” Plant Physiol. 127, 416–425 (2001). 8. I. V. Sherstov, K. V. Bychkov, V. A. Vasil’ev, A. I. Kara puzikov, V. V. Spitsyn, and S. B. Chernikov, “Two Channel CO2 Laser System for Heterodyne Lidar,” Atm. Oceanic Opt. 18, 248–253 (2005).
4) the carbon isotope composition of CO2 desorbed from tree rings of the 1990s is much lighter than that of the 1920s; 5) the isotope composition of hydrogen and oxygen of H2O desorbed from the Siberian stone pine tree rings corresponds to the atmospheric nature. Thus, the investigation of a series of gas compo nents of discs provides for valuable information con nected with both environment variations (climate, atmosphere) and physiological processes.
9. L. S. Rothman, I. E. Gordon, A. Barbe, D. C. Benner, P. F. Bernath, M. Birk, V. Boudon, L. R. Brown, A. Compargue, J.P. Champion, K. Chance, L. N. Cou dert, V. Dana, V. M. Devi, S. Fally, J.M. Flaud, R. R. Gamache, A. Goldman, D. Jacquemart, I. Kleiner, N. Lacome, W. J. Lafferty, J.Y. Mandin, S. T. Massie, S. N. Mikhailenko, C. E. Miller, N. MoazzenAhmadi, O. V. Naumenko, A. V. Nikitin, J. Orphal, V. I. Pere valov, A. Perrin, A. PredoiCross, C. P. Rinsland, M. Rotger, M. Simeckova, M. A. H. Smith, K. Sung, S. A. Tashkun, J. Tennyson, R. A. Toth, A. C. Vandaele, and J. Vander Auwera, “The HITRAN 2008 Molecular Spectroscopic Database,” J. Quant. Spectrosc. Rad. Transfer. 110, 533–572 (2009).
ACKNOWLEDGMENTS This work was performed with the support of the Sibe rian Branch of Russian Academy of Sciences (project nos. VII.63.1.4, VI.44.2.6, and VII.66.1.3) and the Min istry of Natural Resources and Ecology of the Russian Federation (state contract no. 117 160 608). The authors are very thankful to senior researcher S.L. Bondarenko (Institute of Monitoring of Climatic and Ecological Systems, Siberian Branch, Russian Academy of Sciences) for her help in the work. REFERENCES 1. T. Bettger, “Tree Rings as Climate and Environmental Archives—Stable Isotope Dendrological Studies in Germany (Central Europe), New Methods in Dendro ecology,” in Proceedings of the AllRussia Conference with International Participation, Irkutsk, 10–13 Sept. 2007 (Inst. Geografii SO RAN, Irkutsk, 2007), pp. 20–21. 2. D. McCarroll and N. J. Loader, “Stable Isotopes in Tree Rings,” Quater. Sci. Rev. 23, 771–801 (2004). 3. V. V. Zuev, D. A. Savchuk, B. G. Ageev, S. L. Bond arenko, and V. A. Sapozhnikova, “New Dendrochro nological Parameter—the Result of Optoacoustic Measurements of CO2 Concentration in the Annual Rings of Trees,” Atm. Oceanic Opt. 19, 417–420 (2006). ATMOSPHERIC AND OCEANIC OPTICS
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