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

该奖项支持一个项目，以发展对雪/积雪和水蒸气之间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仔细控制的实验室研究，以经验性地测量升华雪的传质系数（水从固体移动到蒸气相的速率），并确定水蒸气和冰之间同位素平衡的时间尺度。 此外，来自升华冰的蒸汽的同位素分馏系数将被确定，其结果将被用来更新现有的模型的质量转移和同位素演变的积雪。 众所周知，水蒸气在积雪中的运动是由于扩散、自由对流和强迫对流。虽然由于这些过程，通过可变饱和积雪的蒸汽运动已经建模，由于缺乏实验室数据的传质系数进行了估计。实地研究已经记录了沉积后变化的幅度，但实地研究不允许严格分析的相对重要性的许多过程可能会在自然积雪。 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物理为基础的模型沉积后的同位素变化，同位素在积雪中的扩散，并在积雪中的蒸汽运动。该项目的一个主要组成部分将是设计和制造必要的新型实验装置，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。 这个项目是一个必要的步骤，对定量了解的同位素效应的水蒸气运动在积雪。拟议的工作在几个不同领域具有更广泛的影响。 模拟结果将适用于极地环境中的水的广泛研究，包括风吹或飘雪的研究。拟议的合作研究将部分支持达特茅斯研究生三年。该项目还将为佛蒙特大学的一名年轻的首次NSF调查员提供支持。来自达特茅斯的本科生也将通过妇女参与科学项目参与进来。主要研究人员和研究生将继续他们的k-12学校推广的传统，每年在当地学校提供科学课程和讲座。 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.