ABSTRACT
Stable isotopes of the light elements are useful tracers of a variety of processes that occur at the surface of the Earth. If two chemical species containing isotopes of the same element have attained isotopic equilibrium with each other, then the difference in their isotopic ratios is a function of the temperature at which they equilibrated. The first practical application by Epstein et al. made possible the determination of the temperatures of growth of some fossil marine organisms. Isotopic analysis of fossil cellulose in wood and peat can thus be used to reconstruct past variations in temperature and humidity. Continental freshwater carbonates Calcium carbonate is chemically precipitated in various forms: spring-deposited tufa and travertine; lacustrine marls; calcareous zones in soil profiles; and speleothem in caves. Carbon isotopes in terrestrial carbonates largely reflect the influence of organic matter on soil CO2, and are controlled by the relative prevalence of C3 versus C4 plants, and variation in aridity or soil productivity.
