Glacial/interglacial temperature variations in Soreq cave speleothems as recorded by ‘clumped isotope’ thermometry
Glacial/interglacial temperature variations in Soreq cave speleothems as recorded by ‘clumped isotope’ thermometry
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DOI：
10.1016/j.gca.2008.06.031
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发表时间：
2007-12
影响因子：
5
通讯作者：
H. Affek;M. Bar-Matthews;A. Ayalon;A. Matthews;J. Eiler
中科院分区：
文献类型：
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作者：
H. Affek;M. Bar-Matthews;A. Ayalon;A. Matthews;J. Eiler
“团块同位素”测温是基于分析从碳酸盐中提取的二氧化碳中的质量47，并使用示踪剂质量47异常（Δ47）。Δ47is定义为r47与随机同位素分布预期值的偏差，反映了13c和18o在co2或碳酸盐晶格中相互形成键的温度依赖偏好。作为碳酸盐矿物的内部特征，它与碳酸盐平衡沉淀发生的水的同位素组成无关，因此可以用来独立确定碳酸盐生长温度。这项工作通过研究以色列Soreq洞穴中化石碳酸盐Δ47values的冰期/间冰期变化，首次检验了“团块同位素”测温法在重建洞穴化石生长温度方面的适用性。结果表明，末次冰期最高温度比现代温度低6 ~ 7℃，56Ky BP样品比现代温度低3℃。全新世早期的温度略高于现代，而全新世晚期的温度略低于现代。这些温度变化与先前对东地中海表层水的估计相似。与现代相比，全新世的洞穴水减少了18o（0.6-1‰），末次盛冰期的洞穴水增加了1.1‰。洞穴水δ18O值与流体包裹体δD值的比较表明，在现代降雨范围内存在晚全新世的d过剩值，意味着相对湿度约为45%。末次冰期最大值和全新世早期d-excess值显著降低，表明相对湿度分别为~ 60%和~ 70%。本研究中报告的温度根据在现代洞穴中观察到的非平衡人工制品进行了经验校正。这里获得的温度变化与该地区其他独立记录的相似性表明，在无机合成方解石和海洋生物中观测到的Δ47-temperature校准斜率也可以应用于洞穴中。但是在现代温度中观察到的偏移表明，截距是不同的，因此需要一个单独的校准来使用洞穴的“团块同位素”进行精确的绝对温度重建。有必要对其他洞穴进行类似的检查，以确定这种经验修正是否可以普遍适用，还是Soreq洞穴的独特特征。
‘Clumped isotope’ thermometry is based on analyzing mass 47 in CO2extracted from carbonates and uses the tracer mass 47 anomaly (Δ47). Δ47is defined as the deviation of R47from that expected for a random distribution of isotopologues and reflects a temperature dependent preference of13C and18O to create a bond with each other in CO2or in the carbonate lattice. Being an internal characteristic of the carbonate mineral, it is independent of the isotopic composition of the water in which equilibrium precipitation of the carbonate occurs and can therefore be used to independently determine carbonate growth temperatures. This work provides a first examination of the applicability of ‘clumped isotopes’ thermometry to reconstructing the growth temperatures of speleothems, by examining the glacial/interglacial variations of the Δ47values of speleothem carbonates from Soreq cave, Israel. The results indicate that the last glacial maximum temperatures were 6–7°C colder than modern day temperature and a sample at 56Ky BP was 3°C colder than the modern. Early Holocene temperatures were slightly above modern day, and late Holocene temperatures were slightly below modern day. These temperature variations are similar to those previously estimated for Eastern Mediterranean sea surface water. Cave water was18O depleted in the Holocene compared to modern day (by 0.6–1‰) and 1.1‰ more enriched in the last glacial maximum. Comparison of these cave water δ18O values with fluid inclusion δD values indicated a late Holocene d-excess value within the range of modern rainfall, implying ∼45% relative humidity. Last glacial maximum and early Holocene d-excess values were significantly lower, suggesting relative humidity of ∼60% and ∼70%, respectively. The temperatures reported in this study were empirically corrected for a non-equilibrium artifact observed in a modern speleothem. The similarity of the temperature variations obtained here to other, independent, records in the region suggests that the Δ47–temperature calibration slope observed in inorganic synthetic calcite and marine organisms may also be applied in speleothems. But the offset observed in modern temperature suggests that the intercept is different so that a separate calibration is needed for accurate absolute temperature reconstruction using speleothem ‘clumped isotopes’. Similar examination of additional caves would be necessary to determine whether such empirical correction can be generally applied or is it a unique characteristic of Soreq cave.