Oxygen isotope analysis of multiple, single ostracod valves as a proxy for combined variability in seasonal temperature and lake water oxygen isotopes
Oxygen isotope analysis of multiple, single ostracod valves as a proxy for combined variability in seasonal temperature and lake water oxygen isotopes
复制标题
DOI：
10.1007/s10933-014-9805-3
复制
发表时间：
2015-01-01
影响因子：
2.1
通讯作者：
Petrie, Cameron A.
中科院分区：
文献类型：
--
作者：
Dixit, Yama;Hodell, David A.;Petrie, Cameron A.
湖泊的古气候研究通常使用由多个介形虫标本组成的样品中的氧同位素比率，以获得平均δ O-18值，该值反映了测量的组合个体的寿命期间湖水的平均温度和δ O-18。这种方法忽略了记录在短寿命介形类的单瓣中的季节性气候变化的潜在信息。在这里，我们估计介形虫三角洲O-18的季节性变化，通过测量10-30个单独的甲壳Cyprideis torosa在选定的地层水平的古湖里瓦萨在哈里亚纳邦，印度的沉积物芯。介形虫种群的平均三角洲O-18值显示出从9.6到8.3 kyr BP的普遍下降，这是以前解释为加强印度夏季风在全新世早期。三角洲O-18测量样品内的单一介形类显示了很大的范围（高达15 aEuro度）和标准差（高达+/- 3.3），这表明高季节性变化的水文干盐湖。大的变化归因于两个季节的温度（16摄氏度）和三角洲O-18的湖水在干燥的水体中的变化。后者是由于瑞利蒸馏过程，描述使用克雷格-戈登模型同位素分馏过程中蒸发从开放的水体。我们的研究结果表明，三角洲O-18值的范围内测量的介形虫甲壳是有用的，以评估湖泊温度和水文的季节变化。然而，即使样本内δ O-18变化很大，多个（超过10个）介形类的平均δ O-18也可以用来推断长期气候趋势。
Paleoclimate studies in lakes typically use oxygen isotopic ratios in samples that consist of multiple ostracod specimens, to obtain an average delta O-18 value that reflects the mean temperature and delta O-18 of lake water over the life spans of the combined individuals measured. This approach overlooks potential information on seasonal climate variability that is recorded in the single valves of short-lived ostracods. Here we estimate seasonal variability in ostracod delta O-18 by measuring 10-30 individual carapaces of Cyprideis torosa in selected stratigraphic levels of a sediment core from paleolake Riwasa in Haryana, India. The mean delta O-18 values of ostracod populations show a general decrease from 9.6 to 8.3 kyr BP, which was interpreted previously as resulting from strengthening of the Indian summer monsoon during the early Holocene. The delta O-18 measurements of single ostracods within samples show a large range (up to 15 aEuro degrees) and standard deviation (up to +/- 3.3), suggesting high seasonal variability in the hydrology of this playa lake. The great variability is ascribed to changes in both seasonal temperature (16 A degrees C) and delta O-18 of lake water in a drying water body. The latter is attributable to the Rayleigh distillation process, described using a Craig-Gordon model for isotopic fractionation during evaporation from an open water body. Our results suggest that the range of delta O-18 values measured in single ostracod carapaces is useful to evaluate seasonal changes in lake temperature and hydrology. Even with great intra-sample delta O-18 variability, however, the mean delta O-18 of multiple (more than 10) ostracods can be used to infer long-term climate trends.