The stable oxygen isotopic composition of ostracoda <i>Limnocythere inopinata</i> Bird and its possible response to water salinity in Lake Qinghai

Abstract

介形类壳体的氧同位素组成已成为恢复湖区古气候/古环境的有效代用指标,而其氧同位素分馏及环境意义目前还缺乏研究.为评价青海湖介形类壳体氧同位素分馏及其环境意义,在青海湖进行系统的表层沉积物和水样的采集,测定表层沉积物中的意外湖花介(Limnocythere inopinata Bird)和相应水样的氧同位素组成.结果表明:意外湖花介壳体的氧同位素组成主要受控于水体的氧同位素组成,除温度的影响外,还可能受到盐度的影响,随着盐度变化,该种壳体与水体之间的同位素分馏呈减小趋势,而两者的氧同位素组成均呈偏正趋势.青海湖意外湖花介壳体的氧同位素组成在一定程度上可能间接反映水体盐度的变化,值得进行更深入的研究.;The oxygen isotopic composition of ostracod shells has been used as a useful indicator in plaeolimnological research. But studies on the oxygen isotopic fractionation of ostracod shells and its environmental significance were still not enough. In this study, surface sediments and co-existing water were systematically collected at different sites in Lake Qinghai. The oxygen isotopic composition of lake water and ostracod shells of Limnocythere inopinata Bird selected from the surface sediments were measured to test the oxygen isotopic fractionation of ostracod shells and evaluate its environmental significance in Lake Qinghai. Our results show that the oxygen isotopic composition of L. inopinata is mainly controlled by the water isotope and the oxygen isotopic fractionation between ostracod shells and water is not only affected by temperature but also maybe by water salinity. The oxygen isotopic fractionation factor of ostracod shells reduces with increasing water salinity, eliminating the effect of temperatures. However, the oxygen isotopic compositions of both ostracod shells and water become enriched with increasing salinity in Lake Qinghai. The oxygen isotopic composition of L. inopinata may be used to indicate the variability of salinity in Lake Qinghai, and further works need to be done in future.