Limits of oxygen isotope palaeoaltimetry in Tibet
Limits of oxygen isotope palaeoaltimetry in Tibet
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DOI：
10.1016/j.epsl.2023.118040
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发表时间：
2023-03
影响因子：
5.3
通讯作者：
A. Farnsworth;P. Valdes;L. Ding;R. Spicer;Shi-Hu Li;Tao Su;Shufeng Li;C. Witkowski;Zhongyu Xio
中科院分区：
文献类型：
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作者：
A. Farnsworth;P. Valdes;L. Ding;R. Spicer;Shi-Hu Li;Tao Su;Shufeng Li;C. Witkowski;Zhongyu Xio
水的稳定同位素（氧和氢）的测量通常用于估计古海拔和量化西藏地表高度的过去变化。同位素古高度测量通常是基于简单的瑞利分馏的“包裹的空气”，但必须作出相当数量的近似和假设。本文阐述了氧水同位素在古测高中的实用性，并评价了古测高界最近面临的挑战。首先，我们研究了氧的同位素组成（δ 18 O）与海拔高度的关系，在一组五个地形实现西藏使用同位素启用古气候模型始新世中期，一个时期，各种地形的“隆起”模型已被提出，并将其与现代的关系。其次，我们调查同位素组成是否是一个很好的预测更温和的地形变化，如引入一个山谷系统或隆起的西藏地区的一部分。本文的目的不是对数据进行直接比较，而是使用该模型进一步完善在古高度测量中使用氧同位素的优势和局限性的知识。我们发现，氧同位素古高度测量的工作令人惊讶的好，除了它不能识别低海拔山谷系统的高海拔地区，因为在空气中的水的同位素组成变得耗尽在第一个高海拔的空气包裹通过，并没有恢复时，它下降到山谷。因此，基于同位素的海拔高度偏向山脉高峰。总的来说，氧同位素古高度测量的应用确实有价值，但如果与同位素启用模型一起使用，将进一步加强。结合其他技术，如地面热直减率和能量守恒的方法，在一个广泛的空间区域，一个更准确的和完整的三维视图的复杂的古地形是越来越可能的，这反过来又会提高这些古高度计的精度。
Measurements of stable water isotopes (oxygen and hydrogen) are commonly used to estimate palaeoelevation and quantify past changes in surface height across Tibet. Isotope palaeoaltimetry is often based on simple Rayleigh fractionation of a “parcel of air”, but must make a considerable number of approximations and assumptions. In this paper, we elaborate on the practicability of oxygen water isotopes in palaeoaltimetry, and evaluate a recent challenge to the palaeoaltimetry community. First, we examine the isotopic composition of oxygen (δ 18 O) versus altitude relationship in a set of five topographic realisations of Tibet using an isotope-enabled palaeoclimate model for the mid-Eocene, a period where a variety of topographic ‘uplift’models have been proposed, and compare it to modern relationships. Second, we investigate whether isotopic composition is a good predictor of more modest changes in topography, such as the introduction of a valley system or uplift of only part of the Tibetan region. The aim of the paper is not to perform a direct comparison to data, but to use the model to further refine knowledge of the strengths and limitations of using oxygen isotopes in palaeoaltimetry. We find that oxygen isotope palaeoaltimetry works surprisingly well, with the exception that it could not identify low elevation valley systems bounded by high elevations because the isotopic composition of the water in the air becomes depleted at the first high elevation that an air parcel passes over and does not recover when it descends into the valley. Hence, isotope-based elevations are biased towards mountain range peaks. Overall, the application of oxygen isotope palaeoaltimetry does have value, but would be further strengthened when employed together with isotope-enabled models. In conjunction with other techniques such as terrestrial thermal lapse rates and energy conservation approaches, over a wide spatial region, a more accurate and fully three-dimension view of complex palaeo-topography is increasingly possible, which will in turn improve the precision of these palaeoaltimeters.