Polar Firn Densification and Grain Growth
Polar Firn Densification and Grain Growth
复制标题
极地冷杉致密化和晶粒生长
作者：
R. Alley;J. Bolzan;I. Whillans
在东南极Dome C采集的一个50 m厚的冰芯中，发现了由粗粒冰芯和细粒冰芯组成的冰芯，粗粒冰芯占冰芯的90 ~ 95%。粗雪的特点是大晶体与垂直形状的表面附近的方向，连接到最近的邻居相对较大的颈部在结构上不同于最紧密的包装。细雪密度较高，由更小、更球形的晶体组成，这些晶体由相对较窄的颈部连接在一起，形成更紧密的结构。在细雪中较高的表面自由能导致晶体和颈部比在粗雪中生长得更快。然而，我们发现，粗雪致密化更迅速地随着时间的推移，与无约束烧结模型的预测。负载驱动的致密化由于幂律蠕变机制被发现占较大的粗Firn致密化率。然而，如果幂律中的指数超过1，则预测致密化速率由于增加的载荷而随着深度增加，这与观察到的行为相反。我们推测，不同的机制可能控制的致密化过程中细和粗积雪。
A 50 m firn core from Dome C, East Antarctica, was found to consist of coarse firn, which comprised 90 to 95% of the core, and fine firn. Coarse firn was characterized by large crystals with a vertical shape orientation near the surface, connected to nearest neighbors by relatively large necks in a structure different from closest packing. Fine firn was of higher density and consisted of smaller, more spherical crystals connected by relatively narrow necks in a more nearly closest-packed configuration. Higher surface free energy in fine firn causes crystals and necks to grow more rapidly than in coarse firn. However, we find that coarse firn densifies more rapidly with time, contrary to the predictions of unconfined sintering models. Load-driven densification due to a power-law creep mechanism is found to account for the larger coarse-firn densification rate. However, if the exponent in the power law exceeds one, then densification rates are predicted to increase with depth due to increasing load, contrary to observed behavior. We speculate that different mechanisms may control the densification process in fine and coarse firn.