Dating ice cores from a high Alpine glacier with a flow model for cold firn
Dating ice cores from a high Alpine glacier with a flow model for cold firn
复制标题
用冷杉流动模型测定高山冰川冰芯的年代
DOI：
10.3189/172756400781820381
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发表时间：
2000
影响因子：
2.9
通讯作者：
M. Funk
中科院分区：
文献类型：
--
作者：
M. Lüthi;M. Funk
冷雪流动模型在计算瑞士阿尔卑斯山Monte Rosa的Colle Gnifetti深冰芯的年龄-深度关系方面是非常成功的。首先由Gagliardini和Meyssonnier（1997）在冰川学中采用的适当的本构方程考虑了积雪的可压缩性，并在有限元程序中实现。Colle Gnifetti鞍状冰川的二维和三维流动模型是基于地表σ和基岩的数字高程图，基于冰厚度的无线电回声探测。在耦合模式中，雪密度和冰内温度场可以是规定的，也可以是计算的。测得的表面速度、密度分布、冰芯中化学定年层的年龄以及100米深钻孔的闭合情况为模型提供了基准。模拟和测量的数量的良好协议证实，该模型包括相关的物理过程，特别是雪流法是非常适合这种类型的冰川。这项研究提供了新的约束的年龄附近的基础，以及在核心的冰的来源区域。在钻孔闭合和倾斜的测量中检测到基底冰层的异常流动行为。测得的变形率超过上限来自流动模型，并因此归因于改变流变性能。
Abstract A flow model for cold firn proves to be very successful in calculating the age-depth relation of several deep ice cores drilled on Colle Gnifetti, Monte Rosa, Swiss Alps. The compressibility of firn is taken into account by an appropriate constitutive equation, first employed in glaciology by Gagliardini and Meyssonnier (1997), which is implemented in a finite-element code. Flow models of the Colle Gnifetti saddle glaciation in two and three dimensions are based on digital elevation maps of the surface σnd the bedrock, based on radio-echo soundings of the ice thickness. Firn density and the englacial temperature fields are either prescribed or calculated in coupled models. Measured surface velocities, density profiles, the ages of chemically dated layers in ice cores and the closure of a 100 m deep borehole provide benchmarks for the models. The good agreement of modeled and measured quantities confirms that the model includes the relevant physical processes and particularly that the firn flow law is well suited for this type of glacier. The study provides new constraints on the age of the ice near the base as well as the source regions of the ice in the cores. An exceptional flow behavior of the basal ice layer was detected in measurements of borehole closure and inclination. Measurtxl6ed deformation rates exceed upper bounds derived from the flow models, and are thus attributed to altered rheological properties.