Collaborative Research: Laboratory Studies of Isotopic Exchange in Snow and Firn

该奖项支持一个项目，该项目旨在发展对雪/雪和水蒸气之间活跃的同位素交换过程的定量理解，这对冰芯解释至关重要。将在各种温度下进行严格控制的实验室研究，以经验地测量升华雪的传质系数(水从固体到汽相的速度)，并确定水蒸气和冰之间同位素平衡的时间尺度。此外，还将确定来自升华冰的水蒸气的同位素分馏系数，其结果将用于更新FIRN中现有的质量传递和同位素演化模型。众所周知，水汽通过降雪是由于扩散、自由对流和强迫对流。尽管由于这些过程导致的水蒸气在可变饱和降温中的运动已被模拟，但由于缺乏实验室数据，必须估计传质系数。实地研究记录了沉积后变化的程度，但实地研究不允许对可能作用于自然积雪的许多过程的相对重要性进行严格分析。这些实验室调查的结果将广泛适用于一些研究，并将允许改进现有的基于物理的沉积后同位素变化、FLAN中的同位素扩散和FLAN中的蒸汽运动的模型。该项目的一个主要组成部分将是设计和制造必要的、新颖的实验仪器，这将由CRREL现有的技术专长、冷藏室设施和实验室设备提供便利。这个项目对于定量理解降雪中水蒸气运动的同位素效应是必要的一步。拟议的工作在几个不同领域产生了更广泛的影响。模拟结果将适用于对极地环境中水的广泛研究，包括对风吹或漂雪的研究。拟议的合作研究将部分支持达特茅斯大学的一名研究生三年。该项目还将为佛蒙特州大学的一名年轻的首次从事NSF研究的人员提供支持。达特茅斯大学的本科生也将通过女性参与科学项目。首席调查人员和研究生将继续他们的K-12学校外展传统，每年在当地学校教授科学课程和讲座。研究成果将通过科学会议、期刊出版物和机构研讨会传播。

This award supports a project to develop a quantitative understanding of the processes active in isotopic exchange between snow/firn and water vapor, which is of paramount importance to ice core interpretation. Carefully controlled laboratory studies will be conducted at a variety of temperatures to empirically measure the mass transfer coefficient (the rate at which water moves from the solid to the vapor phase) for sublimating snow and to determine the time scale for isotopic equilibration between water vapor and ice. In addition the isotopic fractionation coefficient for vapor derived from sublimating ice will be determined and the results will be used to update existing models of mass transfer and isotopic evolution in firn. It is well known that water vapor moves through firn due to diffusion, free convection and forced convection. Although vapor movement through variably-saturated firn due to these processes has been modeled, because of a lack of laboratory data the mass transfer coefficient had to be estimated. Field studies have documented the magnitudes of post-depositional changes, but field studies do not permit rigorous analysis of the relative importance of the many processes which are likely to act in natural snow packs. The results of these laboratory investigations will be broadly applicable to a number of studies and will allow for improvement of existing physically-based models of post-depositional isotopic change, isotopic diffusion in firn, and vapor motion in firn. A major component of this project will be the design and fabrication of the necessary, novel experimental apparatus, which will be facilitated by existing technical expertise, cold room facilities, and laboratory equipment at CRREL. This project is a necessary step toward a quantitative understanding of the isotopic effects of water vapor movement in firn. The proposed work has broader impacts in several different areas. The modeling results will be applicable to a wide range of studies of water in the polar environment, including studies of wind-blown or drifting snow. The proposed collaborative study will partially support a Dartmouth graduate student for three years. This project will also provide support for a young first-time NSF investigator at the University of Vermont. Undergraduate students from Dartmouth will also be involved through the Women in Science Project. The principal investigators and graduate student will continue their tradition of k-12 school outreach by giving science lessons and talks in local schools each year. Research results will be disseminated through scientific conferences, journal publications, and institutional seminars.