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

ABSTRACTAlbertOPP-0520445SeveringhausOPP-0520564BattleOPP-0520460Intellectual优点：我们这个时代的一个重要问题涉及人类活动如何受到我们星球的大气组成的影响的问题。作为国际极地年的一部分，一个主要领域涉及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有限，必须建立大气组成的自然档案，如极地降雪。它的透气性，深达数十米，允许气体随时间的间隙扩散，最古老的空气位于降雪柱底部，这使得可以对大量工业化前的空气进行采样，以探索对大气的人为影响。这个项目将调查控制FEN存储过去大气样本能力的潜在物理因素。首席调查员将对顶峰从表面到孔洞闭合的扩散率剖面、渗透率剖面和伴生微结构进行高分辨率测量，并将结果与从降雪空气化学成分测量推断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)量化降雪微观结构对间隙传输过程的依赖，并确定气体扩散率对从表面到孔隙闭合深度的微结构特征的依赖；2)量化积雪和降雪物理性质的沉积后变化，并使用测量的降雪和气象数据来评估和开发驱动温度梯度较大的坚固化的物理传输过程模型。3)在确定降雪特征时进行降雪空气化学测量，并将从降雪空气化学测量中推断的共同记录的扩散系数剖面与在降雪核心本身上进行的高分辨率示踪气体测量进行比较。4)利用降雪空气组成和降雪结构的测量，更好地量化大气组成(现在和过去)与滞留在降雪和冰内气泡中的空气之间的差异。更广泛的影响：这项研究将建立定量关系，使我们能够更好地理解降雪作为过去大气成分的储存库，同时也使我们能够了解可能影响其他地点降雪空气组成的机制。研究结果将发表在期刊论文上，并广泛提供。这个项目将成为达特茅斯大学一名学生博士论文的一部分。将有几名本科生参与其中。他们将与来自瑞士和法国的学生互动，设计和建造一个IPY博物馆展览，在佛蒙特州诺维奇的蒙特希尔科学博物馆。展览将是互动的，并将展示雪和雪作为过去重要事件档案的能力。它将允许观众扮演“侦探”的角色，追踪冰雪空气中不同化学成分轮廓的含义。

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.