Abstract
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 (δ18Ocarb) and its spatial distribution. Our results show that water oxygen isotopic composition (δ18Owater) rather than lake summer water temperature (Twater), is the main determinant of δ18Ocarb, irrespective of whether oxygen isotope equilibrium is achieved. There are significant linear correlations between δ18Ocarb and elevation, as well as that between δ18Ocarb and latitude for lakes located on the Tibetan Plateau. In Western China, the spatial distribution of δ18Ocarb is consistent with that of δ18Owater, and is ultimately controlled by the isotopic composition of local precipitation (δ18Oprecipitation) that depends on the source of water vapor. Therefore, changes in δ18Ocarb can be predominantly interpreted as variations of δ18Owater, which in turn represent changes in δ18Oprecipitation for paleoclimate reconstructions in this region, and may be relevant to studies of other areas.
Highlights
In the carbonate-water system, at equilibrium, the oxygen isotopic composition of carbonate is dependent on the temperature and on the isotopic composition of host water in which the carbonate is formed
Two critical factors controlling the oxygen isotopic composition of carbonate mineral are the temperature of carbonate formation and the oxygen isotopic composition of the solution from which carbonate minerals precipitate[5]
We discuss the effects of these two factors respectively and spatial distributions of the oxygen isotopic composition of lacustrine carbonates in Western China
Summary
In the carbonate-water system, at equilibrium, the oxygen isotopic composition of carbonate is dependent on the temperature and on the isotopic composition of host water in which the carbonate is formed. 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 (δ18Ocarb) and its spatial distribution. A number of empirical relationships between carbonate oxygen isotopic composition and temperature have been established[5,6,7,8], and are widely applied to lakes in paleoclimate studies to reconstruct water temperature[9,10,11]. Most laboratory experiments and theoretical calculations are based on limiting multiple external conditions with only one variable; natural settings are more complex This may result in inconsistencies of calculated oxygen isotope fractionation factors among different laboratories, as well as that between natural records and laboratory experiments[18,21]. Some field studies show that the oxygen isotopic compositions of lacustrine carbonates are largely influenced by rainfall or local precipitation/ evaporation balance, rather than temperature c hanges[24,25]
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