Climatic implications of the D/H ratio of hydrogen in C-H groups in tree cellulose

Abstract

Isotopic climate records in tree rings were obtained by the δD analyses of the hydrogen in cellulose nitrate extracted from tree rings in a Scots pine from Loch Affric, Scotland, and from a bristlecone pine from the White Mountains, California. This method of analysis measures δD values of only the isotopically non-exchangeable hydrogen of the cellulose in wood and thus eliminates serious complications in the δD record caused by the chemical heterogeneity of wood and by the isotopic exchangeability of some of its hydrogen. The average δD values of the two pines are markedly different, reflecting the contrasting climates of the two areas. The bristlecone δD record contains a 22-year periodicity perhaps recording a possible 20- to 22-year periodicity of drought conditions in the Great Plains of North America. There is no such significant periodicity in the δD record of the Scots pine. The long-term δD trends in the two pines, as represented by 40-year running averages of the δD data, correlate linearly over the time period 1841–1970 A.D., which is the total growth period of the Scots pine. The long-term δD trend of the Scots pine correlates well with the 1841–1970 winter temperatures of Edinburgh, Scotland. The long-term δD trend of the bristlecone pine, which extends over the time period 970–1970 A.D., correlates qualitatively with long-term climatic trends estimated by LaMarche from tree ring width data and by Lamb from many sources of climatic data. δD analyses were also made on early and late woods from the same annual ring. The δD values of these woods differ to various degrees and the sign of the difference can also vary.