Exploring the potential of 17O-excess in ice to constrain post-depositional alteration and loss by sublimation.

利用低、中纬度冰雪沉积物中水的常见稳定同位素比值（D/H，18 O/16 O）来估算山地冰川水资源和冰芯古气候重建，目前受到沉积后同位素分馏反应复杂性的限制。沉积后的升华损失可能是最广泛认可的改变冰雪同位素组成的过程。由于同位素分馏对温度的依赖性，这种通过升华和通过其他过程（例如熔融-再冷冻循环）的沉积后改性难以使用常规的H和O同位素系统来校正。17 O过量参数-类似于从δ D和δ 18 O导出的d过量-从三重O同位素系统（16 O-17 O-18 O）计算，对地球表面上发现的典型范围内的温度变化几乎不敏感。这允许识别动力学控制的同位素交换，例如在蒸发期间，而不必考虑温度依赖的平衡分馏。我们建议，以确定三重O-同位素分馏因子和17 O-过剩的升华和熔融冻结过程中的一系列精心设计的实验室实验的演变。然后，我们试图测试的一般适用性的17 O-过量约束二次同位素蚀变的雪和冰在自然的高海拔环境中-在Schneefernerhaus研究站，德国阿尔卑斯山-由高分辨率的监测研究在几个两个星期长的时间间隔，辅以定期低分辨率的雪采样在一年的过程中。最后，我们试图调查最近的冰，以及日期的全新世洞穴冰存款在斯卡里索拉冰洞，罗马尼亚，目的是限制17 O-过剩的沉积后的同位素变化的冰在每年发生的融化-再冻结周期，目前阻碍了使用稳定的H和O同位素比值作为古气候代理在这个位置。

The use of common stable isotope ratios of water (D/H, 18O/16O) in low and mid-latitude snow and ice deposits for budgeting water resources from mountain glaciers and for paleoclimate reconstruction from ice cores is currently limited by the complexity of isotope fractionation reactions occurring after deposition. Post-depositional loss due to sublimation is perhaps the most widely recognized process that modifies the isotopic composition of snow and ice. Such post-depositional modification by sublimation - and by other processes, such as melting-refreezing cycles - are difficult to correct for using the conventional H and O isotope systems because of a dependency of isotope fractionation on temperature. The 17O-excess parameter - similar to d-excess derived from deltaD and delta18O - calculated from the triple O-isotope system (16O-17O-18O), is nearly insensitive to temperature changes in the typical range found on the earth's surface. This allows to identify kinetically controlled isotope exchange, for example during evaporation, without having to consider temperature dependent equilibrium fractionation. We propose to determine triple O-isotope fractionation factors and the evolution of 17O-excess during sublimation and melting-freezing in a series of carefully designed laboratory experiments. We then seek to test the general applicability of 17O-excess to constrain secondary isotopic alteration of snow and ice in the natural high-altitude environment - at Schneefernerhaus research station, German Alps - by a high-resolution monitoring study over a few two-week-long intervals, complemented by regular low resolution snow sampling over the course of a year. Finally, we seek to investigate the most recent ice from the well dated holocene cave ice deposit at Scarisoara ice cave, Romania, with the objective to constrain by 17O-excess the post-depositional isotopic alteration of ice during the annually occurring melting-refreezing cycles that currently hampers the use of stable H and O isotope ratios as paleoclimatic proxies at this location.