Time variations of stable isotope contents in an organic matter

The effect of climatic factors on the content of stable isotopes in an organic substance is discussed. It is found out that stable isotopes can be used as a thermometer in paleoclimatology. As a thermometer the method can be used of the quantitative determination of temperature of marine basins in the past on the proportion of 18O and 16O oxygen isotopes in the carbonate of fossil invertebrates. The efficiency of the method is limited due to the absence of knowledge of time dependence of the oxygen isotope composition of ancient waters. Recently an attempt has been made to use the vegetative substance of the organic origin as a paleoclimatic indicator. It is found that in the process of the transformation of a vegetative substance into peat the deuterium concentration is constantly lowering while the carbon content increases. The carbon content of peat may indicate the initial deuterium concentration. However, this procedure is not accurate enough because of inhomogeneity of chemical composition of plants. The analysis is proposed to be based on the use of unexchangeable carbon-bound hydrogen of cellulose because its D/H ratio does not change in the process of biosynthesis. The studies testify that the variation of the content of stable isotopes in an organic substance contains the information on climates in the past