Tree-ring data, isotope

For more than 80 years, tree-ring data have been used to make inferences about past climatic variation. In general, the characteristic most often used has been the variations in widths of the annual growth rings. However, during the past decade other properties, such as cell density (measured by x-ray densiometric techniques), relative widths of early and late wood, and isotopic composition of the cellulose have been used to infer past environmental conditions. It is the isotopic composition that is of interest here. 

Estimate of global temperature based on proxy data such as tree rings and isotope ratios in sediments and ice cores. The 1990s was the warmest decade in 2000 years. [From M. E Mam and P D. Jones,"Global Surface Temperatures Over the Past Two Millennia," Geophys. Res. Lett. 2003,30.1820.]... 

Epstein and Yapp [4] state "it is obviously necessary to calibrate more specifically the relationship between 6(D) records in cellulose nitrate from tree-ring records and known climatic records. This can probably be done best by the analysis of tree rings from widely different, well-documented environments. Such data will allow the comparison of a large variety of trees and determine the versatility of using the isotopic method for climatic temperature determination". We concur with this statement as long as "from the same population" is inserted. 

Radiocarbon years are calibrated from determinations of the 14C activity and stable isotopic carbon ratios of dendrochrono-logically dated tree rings [4]. The stable isotope data are required to normalize the dates to average wood with 613C value of -25 per mil (13C/12C fractionation relative to PDB reference standard). Photosynthetic and other plant physiological processes may produce differential isotopic fractionation between species, within the same species in different localities and even within the same tree under changing environmental conditions. 

Sea cores offer a data base which should in principle allow deduction of the history of the local sea surface temperature immediately above the deposition site of the core, for there is enough organic material in sea cores to provide the necessary samples for isotope measurement at frequent intervals versus depth in the core, but the time resolution is far less accurate than in varves and tree rings because burrowing sea bottom animals smear the record of the layers. 

On Mey 17, 1971, the Defense Advanced Research Projects Agency [15] funded our proposal that "temperature variations may be evaluated by measuring stable isotope ratios in natural data banks such as tree rings and varves". L. M. Libby had previously calculated [16] the theoretical temperature coefficients of the stable isotope fractionations in manufacture of wood from C02 and H20, finding that the coefficients are small compared with those measured in rain and snow [17]. 

The isotopic isolation of in each tree ring had crucial implications for future radiocarbon studies and continues to be very much a part of current research. Specifically, the examination of the radiocarbon contents in tree-ring-dated samples of wood provided the principal data that permits an in-depth examination of the assumption that the production of radiocarbon by cosmic rays had been maintained at a constant level. For archaeologists especially, it is important to know if there have been... 

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