Collaborative Research: Firn structure, interstitial processes and the composition of firn air at Summit, Greenland

知识价值：我们这个时代的一个重要问题涉及到人类活动如何受到地球大气成分影响的问题。 国际极地年的一个主要领域是更好地了解过去的气候和人类活动对地球大气层的影响。由于大气化学的仪器记录是有限的，必须建立大气成分的自然档案，如极地积雪。它的多孔性，几十米深，允许气体随着时间的推移与最古老的空气在雪柱底部的间隙扩散，这使得大量的工业化前的空气采样，以探索人类对大气的影响。该项目将调查控制积雪储存过去大气样本能力的基本物理学。主要研究人员将在峰会上对从表面到孔隙封闭的扩散率剖面、渗透率剖面和伴随的微观结构进行高分辨率测量，并将结果与从积雪空气化学成分测量中推断出的扩散率剖面进行比较。他们将与瑞士联邦研究所的Atsumu Ohmura博士和法国LGGE的Christophe Ferrari博士合作。 该项目有四个目标：1）定量地确定间隙输运过程对雪微观结构的依赖性，并确定从表面向下到孔隙封闭深度的气体扩散率对微观结构特征的依赖性; 2）量化后雪和积雪的物理性质的沉积变化，并使用测量的积雪性质和气象数据来评估和开发驱动积雪化的物理传输过程的模型，温度梯度很大。3)在确定积雪特征时进行积雪空气化学测量，并将从积雪空气化学测量推断的共记录扩散率剖面与对积雪芯本身进行的高分辨率示踪气体测量进行比较。4)利用对积雪空气成分和积雪结构的测量，更好地量化大气成分（现在和过去）之间的差异，以及积雪和冰内气泡中捕获的空气。更广泛的影响：这项研究将建立定量关系，使我们能够更好地了解积雪作为过去的大气成分的储存库，但也将使我们能够了解可能影响其他地点的积雪空气成分的机制。研究结果将发表在期刊文章中，并广泛提供。这个项目将成为达特茅斯一名学生博士论文的一部分。几个本科生将参与其中。 他们将与来自瑞士和法国的学生互动，在佛蒙特州诺里奇的蒙特希尔科学博物馆设计和建造一个IPY博物馆展览。该展览将是互动的，并将展示雪和积雪作为过去重要事件档案的能力。它将允许观众充当“侦探”，以追踪积雪空气中不同化学成分剖面的含义。

ABSTRACTAlbertOPP-0520445SeveringhausOPP-0520564BattleOPP-0520460Intellectual merit: An important issue of our time involves questions of how human activity has been impacted by the atmospheric composition of our planet. A major area as part of the International Polar Year (IPY) involves developing a better understanding of past climates and the impact of anthropogenic activity on the Earth's atmosphere. Because instrumental records of atmospheric chemistry are limited, natural archives of atmospheric composition must be made, such as polar firn. Its porous nature, tens of meters in depth, permits interstitial diffusion of gases over time with the oldest air at the bottom of the firn column which allows the sampling of large quantities of pre-industrial air to explore anthropogenic effects on the atmosphere. This project will investigate the underlying physics controlling firn's ability to store atmospheric samples from the past. The Principal Investigators will make high-resolution measurements of the diffusivity profile, permeability profile, and accompanying microstructure at Summit from the surface to pore close-off, and compare the results to the diffusivity profile inferred from measurements of firn air chemical composition. They will partner with Dr. Atsumu Ohmura, Swiss Federal Institute, and Dr. Christophe Ferrari of LGGE, France. This project has four goals: 1) Quantify the dependence of interstitial transport processes on firn microstructure, and determine the dependence of gas diffusivity on microstructure characteristics from the surface down to the pore close-off depth; 2) Quantify post-depositional changes in the physical properties of snow and firn and use measured properties of firn and meteorological data to evaluate and develop models of the physical transport processes which drive firnification where temperature gradients are large. 3) Conduct firn air chemical measurements as the firn characteristics are determined, and compare the co-registered diffusivity profile inferred from the firn air chemistry measurements to the high-resolution tracer gas measurements made on the firn core itself. 4) Use the measurements of firn air composition and firn structure to better quantify the differences between atmospheric composition (present and past), and the air trapped in both the firn, and in air bubbles within ice. Broader Impacts: This study will establish quantitative relationships that will enable a better understanding of the firn as a repository of past atmospheric composition, but will also enable us to understand mechanisms that may impact firn air composition at other sites. Results of the research will be published in journal articles and made widely available. This project will form one part of the PhD dissertation of a student from Dartmouth. Several undergraduates will be involved. They will interact with students from Switzerland and France to design and construct an IPY museum exhibit, at the Montshire Museum of Science in Norwich, Vermont. The exhibit will be interactive and will illustrate the ability of snow and firn to serve as an archive of important events of the past. It will allow the viewer to act as the "detective" to track down the meaning of different chemical composition profiles in the firn air.