Molecular diffusion of stable water isotopes in polar firn as a proxy for past temperatures
Molecular diffusion of stable water isotopes in polar firn as a proxy for past temperatures
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DOI：
10.1016/j.gca.2018.01.015
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发表时间：
2018-03-15
影响因子：
5
通讯作者：
Vinther, Bo M.
中科院分区：
文献类型：
--
作者：
Holme, Christian;Gkinis, Vasileios;Vinther, Bo M.
存档在冰盖中的极地降水包含了过去温度条件的信息。这些信息可以通过测量冰芯中δ O-18和δ D的水同位素信号来检索。这些信号已在致密化过程中，由于在雪柱中的分子扩散，其中扩散的幅度是同位素特异性和温度依赖性的衰减。通过利用差分扩散信号，Δ O-18和Δ D的双同位素测量使得能够实现多种温度重建技术。这项研究评估了如何以及六种不同的方法可以用来重建过去的表面温度从扩散为基础的温度代理。其中两种方法是基于Δ O-18和Δ D的单扩散长度，三种方法使用差分扩散信号，而最后一种方法使用单扩散长度之间的比率。所有的技术进行测试合成数据，以评估其准确性和精度。我们进行了基准测试，以13个高分辨率全新世数据集从格陵兰岛和南极洲，这代表了广泛的年平均地表温度和积累率。在基准测试的基础上，对方法的准确度和精密度进行了评价。基准测试和合成数据测试都表明，当使用单个同位素扩散长度时，获得最精确的重建，精度约为1.0 ℃。在基准测试中，单个同位素扩散长度也被发现以0.7摄氏度的均方根偏差重建一致的温度。采用差分扩散信号的技术更不确定，其中最精确的方法具有1.9摄氏度的精度。扩散长度比法的精度最低，为13.7 ℃。从这种方法的绝对温度估计也被证明是高度敏感的分馏因子参数化的选择。(C)2018作者（S）爱思唯尔有限公司出版
Polar precipitation archived in ice caps contains information on past temperature conditions. Such information can be retrieved by measuring the water isotopic signals of delta O-18 and delta D in ice cores. These signals have been attenuated during densification due to molecular diffusion in the firn column, where the magnitude of the diffusion is isotopologue specific and temperature dependent. By utilizing the differential diffusion signal, dual isotope measurements of delta O-18 and delta D enable multiple temperature reconstruction techniques. This study assesses how well six different methods can be used to reconstruct past surface temperatures from the diffusion-based temperature proxies. Two of the methods are based on the single diffusion lengths of delta O-18 and delta D, three of the methods employ the differential diffusion signal, while the last uses the ratio between the single diffusion lengths. All techniques are tested on synthetic data in order to evaluate their accuracy and precision. We perform a benchmark test to thirteen high resolution Holocene data sets from Greenland and Antarctica, which represent a broad range of mean annual surface temperatures and accumulation rates. Based on the benchmark test, we comment on the accuracy and precision of the methods. Both the benchmark test and the synthetic data test demonstrate that the most precise reconstructions are obtained when using the single isotope diffusion lengths, with precisions of approximately 1.0 degrees C. In the benchmark test, the single isotope diffusion lengths are also found to reconstruct consistent temperatures with a root-mean-square-deviation of 0.7 degrees C. The techniques employing the differential diffusion signals are more uncertain, where the most precise method has a precision of 1.9 degrees C. The diffusion length ratio method is the least precise with a precision of 13.7 degrees C. The absolute temperature estimates from this method are also shown to be highly sensitive to the choice of fractionation factor parameterization. (C) 2018 The Author(s). Published by Elsevier Ltd.