Factors controlling the oxygen isotopic composition of lacustrine authigenic carbonates in Western China: implications for paleoclimate reconstructions

In the carbonate-water system, at equilibrium, the oxygen isotopic composition of carbonate is dependent not only on the temperature but also on the isotopic composition of host water in which the carbonate is formed. In this study, lake surface sediment and water samples were collected from 33 terminal lakes in Western China to evaluate controls on the oxygen isotopic composition of lacustrine authigenic carbonates (δ(18)O(carb)) and its spatial distribution. Our results show that water oxygen isotopic composition (δ(18)O(water)) rather than lake summer water temperature (T(water)), is the main determinant of δ(18)O(carb), irrespective of whether oxygen isotope equilibrium is achieved. There are significant linear correlations between δ(18)O(carb) and elevation, as well as that between δ(18)O(carb) and latitude for lakes located on the Tibetan Plateau. In Western China, the spatial distribution of δ(18)O(carb) is consistent with that of δ(18)O(water), and is ultimately controlled by the isotopic composition of local precipitation (δ(18)O(precipitation)) that depends on the source of water vapor. Therefore, changes in δ(18)O(carb) can be predominantly interpreted as variations of δ(18)O(water), which in turn represent changes in δ(18)O(precipitation) for paleoclimate reconstructions in this region, and may be relevant to studies of other areas.