On the nature of the dirty ice at the bottom of the GISP2 ice core
On the nature of the dirty ice at the bottom of the GISP2 ice core
复制标题
论GISP2冰芯底部脏冰的性质
DOI：
10.1016/j.epsl.2010.09.033
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发表时间：
2010
影响因子：
5.3
通讯作者：
G. Clow
中科院分区：
文献类型：
--
作者：
M. Bender;E. Burgess;R. Alley;Bruce A. Barnett;G. Clow
我们提供了 GISP2 冰芯 2800 至 3040m 深度之间干净的地层扰动冰以及 3040 至 3053m 深度基底脏冰中捕获气体中的三重 Ar 同位素组成数据。我们还提供了基底脏冰中 O2 和 N2 的丰度和同位素组成以及 Ar 丰度的数据。脏基底冰的Ar/N2比、重同位素富集度（反映重力分馏）和总气体含量都表明基底脏冰中的气体来源于上覆冰川的清洁冰的同化，而上覆冰川的干净冰构成了脏底层的大部分冰。基础冰中的氧气部分至完全耗尽，反映出新陈代谢活跃。 40Ar/38Ar 的重力校正比在全球大气中随着年龄的增长而减小，与清洁扰动冰的 100-250ka 年龄相一致。在基底冰中，由于下方大陆地壳中产生的放射性 40 Ar 的注入，40 Ar 过量存在。肮脏的基底冰中 40Ar 的弱深度梯度以及污垢的分布表明基底冰内存在混合，而各种已发表的证据表明上覆的干净、受干扰的冰内存在混合。在 GRIP 的基础脏冰中，过量的 CH4 达到数千 ppm，而在上层干净的扰动冰中几乎不存在，这表明脏基础冰与上层干净冰的混合（如果确实发生）是非常缓慢的。数量级估计表明，干净冰与脏冰的混合速率足以维持脏冰的稳定厚度，防止平均冰流变薄。除了干净的冰川冰之外，脏冰似乎还包含两种或多种基本成分。少量的土壤或永久冻土，加上冰期前的雪、湖泊或地面冰可以解释这些观察结果。
We present data on the triple Ar isotope composition in trapped gas from clean, stratigraphically disturbed ice between 2800 and 3040m depth in the GISP2 ice core, and from basal dirty ice from 3040 to 3053m depth. We also present data for the abundance and isotopic composition of O2and N2, and abundance of Ar, in the basal dirty ice. The Ar/N2ratio of dirty basal ice, the heavy isotope enrichment (reflecting gravitational fractionation), and the total gas content all indicate that the gases in basal dirty ice originate from the assimilation of clean ice of the overlying glacier, which comprises most of the ice in the dirty bottom layer. O2is partly to completely depleted in basal ice, reflecting active metabolism. The gravitationally corrected ratio of40Ar/38Ar, which decreases with age in the global atmosphere, is compatible with an age of 100–250ka for clean disturbed ice. In basal ice,40Ar is present in excess due to injection of radiogenic40Ar produced in the underlying continental crust. The weak depth gradient of40Ar in the dirty basal ice, and the distribution of dirt, indicate mixing within the basal ice, while various published lines of evidence indicate mixing within the overlying clean, disturbed ice. Excess CH4, which reaches thousands of ppm in basal dirty ice at GRIP, is virtually absent in overlying clean disturbed ice, demonstrating that mixing of dirty basal ice into the overlying clean ice, if it occurs at all, is very slow. Order-of-magnitude estimates indicate that the mixing rate of clean ice into dirty ice is sufficient to maintain a steady thickness of dirty ice against thinning from the mean ice flow. The dirty ice appears to consist of two or more basal components in addition to clean glacial ice. A small amount of soil or permafrost, plus preglacial snow, lake or ground ice could explain the observations.