Trees rings

Though measurements of solar output have been taken only for the past eighteen years, longer trend patterns can be derived from indirect data sources, such as ice cores and tree rings. Cosmic rays, which fluctuate with the sun s activity, also strike constituents of the atmosphere, creating radioactive versions of certain elements. Beiyllium, in particular, is ionized to "Be by cosmic rays. The "Be then gets incorporated into trees as they grow, and is trapped in bubbles in ice masses, as is carbon dioxide. 

Fig. 11-26 Decade-averaged data of Northern hemisphere tree ring records from 1750-1979 and 7th-degree polynomial fit of the data. The vertical extension of blocks represents 95% confidence limits of the mean. The open circles give the change of —0.65% in atmospheric CO2 observed from 1956 to 1978 by Keeling et al. (1979). (Adapted from Peng et al, 1983.)...

Records of past environmental change are preserved in a broad range of Earth materials. Past environments are inferred from "proxy" records, meaning measurements of physical and chemical parameters of marine and terrestrial sediment, polar ice, and other materials that were in some way influenced by their environment during accumulation. Examples of proxy records are the distribution of glacial deposits, the isotopic composition of terrestrial and marine sediments and ice, the abundance and species composition of plant and animal fossils, and the width of tree rings. 

Becker, B., Kromer, B. and Trimbom, P. 1991 A stable-isotope tree-ring timescale of the Late Glacial/Holocene boundary. Nature 353 647-649. 

Leavitt, S.W. and Long, A. 1991 Seasonal stable-carbon isotope variability in tree rings possible palaeoenvironmental signals. Chemical Geology (Isotope Geoscience Section) 87 59-70. 

Loader, N.J., Switsur, V.R. and Field, E.M. 1995 High-resolution stable isotope analysis of tree rings implications of microdendroclimatology for palaeoenvironmental research. The Holocene 5 457-460. 

Saurer, M., Siegenthaler, U. and Schweingruber, F. 1995 The climate-carbon isotope relationship in tree rings and the significance of site conditions. Tellus 47B 320-330. 

Baillie, M. G. L. (1995), Tree rings in archaeology, Univ. Chicago Press, Chicago. 

Fritts, H. C. (1976), Tree Rings and Climate, Academic Press, New York. 

Schweingruber, F. H. (1988), Tree Rings, Basics and Applications of Dendrochronology, Reidel, Dordrecht. 

From observed variations of 14C/C in tree-ring samples we have indications of a 200 y cycle in the radioisotope production and P /P0 is suggested to be of the order of 25 percent [13]. 

During the last 15 years intensive studies on the history of the atmospheric 14C/C ratio have been performed on tree-rings [20]. The results can be summarized as follows from 7000 BP (before present) to 2000 BP the average atmospheric 14C/C ratio had decreased by about 10 percent. Superimposed on this general trend are secular variations (Suess-Wiggles) of the order of 1 to 2 percent. In some time intervals a basic period of about 200 years is visible. 

Figure 10. Carbon-14 production as calculated from tree-ring 14C concentrations by means of the...

There would be, however, a considerable discrepancy between the model-calculated dilution factor and the dilution factor required if the biospheric C02 input were of comparable size as the fossil C02 input as stated by biologists [43]. For a discussion of this question see also Oeschger et al., [39]. Thirdly, we calculate the 14C dilution corresponding to the CO increase. In 1950, before the nuclear weapon tests, the integrated C02 production amounted to about 10 percent of the preindustrial atmospheric C02 content. If there had been no exchange with other reservoirs, a decrease of the 14C/C ratio by 10 percent would have resulted. Tree-ring 14C measurements indicated, however, a decrease by only about 2 percent. Again we calculate the system dilution. In a first approximation 4 and s are set equal to one and we obtain... 

---