On the impact of impurities on the densification of polar firn
On the impact of impurities on the densification of polar firn
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DOI：
10.1016/j.epsl.2011.12.022
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发表时间：
2012-04
影响因子：
5.3
通讯作者：
M. Hörhold;T. Laepple;J. Freitag;M. Bigler;H. Fischer;S. Kipfstuhl
中科院分区：
文献类型：
--
作者：
M. Hörhold;T. Laepple;J. Freitag;M. Bigler;H. Fischer;S. Kipfstuhl
了解极地积雪致密化对于重建从冰芯中提取的温室气体浓度的年龄，以及将冰中的空气解释为测年工具或气候代用指标至关重要。积雪致密化通常被模拟为一个稳定的埋藏和烧结过程的定义层，其中的分层结构保持沿着整个积雪和冰柱。然而，现有的高分辨率密度数据，以及积雪的空气样本，质疑这一情况，并指出缺乏理解的积雪致密化。基于对南极和格陵兰冰芯高分辨率密度和钙浓度记录的分析，我们首次表明杂质也可能对致密化产生重大影响。对雪芯的分析表明，密度和钙离子（Ca++）浓度之间存在相关性，这种相关性随着深度的增加而增加。这种关系的存在是独立的当地气候条件的核心网站分析。密度和Ca++浓度的对数之间的强正相关性表明，杂质诱导软化，并导致更快的致密化在很宽的浓度范围内。在一个地核中，杂质效应表现得如此强烈，以至于密度的季节性循环紧密地跟随着Ca++的季节性循环。我们的研究结果清楚地表明，积雪分层的结构随深度的变化，并表明，在深积雪，最近被描述为极地积雪的一个普遍特征，密度的变化增加，可能会产生Ca++和/或其他杂质的影响。杂质效应可能对我们理解冰川积雪致密化和冰川气体年龄估计有直接影响。
Understanding polar firn densification is crucial for reconstructing the age of greenhouse gas concentrations extracted from ice cores, and for the interpretation of air in ice as a dating tool or as a climate proxy. Firn densification is generally modeled as a steady burial and sintering process of defined layers, where the structure of the layering is maintained along the whole firn and ice column. However, available high-resolution density data, as well as firn air samples, question this picture and point to a lack of understanding of firn densification. Based on analysis of high-resolution density and calcium concentration records from Antarctic and Greenland ice cores, we show for the first time that also impurities may have a significant impact on the densification. Analysis of firn cores shows a correlation between density and the calcium ion (Ca++) concentration, and this correlation increases with depth. The existence of this relationship is independent of the local climatic conditions at the core sites analyzed. The strong positive correlation between the density and the logarithm of Ca++ concentration indicates that impurities induce softening and lead to faster densification over a wide range of concentrations. In one core, the impurity effect manifests itself so strongly that the density develops a seasonal cycle closely following the seasonal cycle of Ca++. Our results clearly show that the structure of the firn layering changes with depth and suggest that the increased variability in density observed in deep firn, recently described as a universal feature of polar firn, may arise from the influence of Ca++ and/or other impurities. The impurity effect is likely to have direct implications on our understanding of glacial firn densification and on glacial gas age estimates.