| Abstract: |
The isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments. This article reviews the controls on the isotope composition of lacustrine skeletal and non-skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature, precipitation patterns, evaporation and the carbon cycle. It highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins. A large number of the case histories, but not all, are drawn from studies of temperate lakes from Europe. Large closed lake systems, in the tropics andelsewhere, lose water predominantly through evaporation, and contain sediments with variable and generally high d18O values. Fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long-term changes in the precipitation/evaporation ratio. In contrast small open lakes which have a degree of through-flow typically contain sediments with d18O values that vary by no more than a few %. These variations are generally ascribed to variations in temperature or the isotope composition of precipitation (dp), from which either an annual or seasonally specific signal can be gained. These types of lakes are common in Northern Europe and at high altitudes. The interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal. Their effects need to be quantified, and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal, the isotopic composition of the host waters, and climate.
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