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

该奖项支持了一个项目，该项目旨在定量了解雪/雪和水蒸气之间同位素交换的活跃过程，这对冰芯解释至关重要。精心控制的实验室研究将在各种温度下进行，以经验测量升华雪的传质系数（水从固体向气相移动的速率），并确定水蒸汽和冰之间同位素平衡的时间尺度。此外，还将测定升华冰产生的蒸汽的同位素分馏系数，其结果将用于更新现有的铁中传质和同位素演化模型。众所周知，水蒸气在大气中的运动主要有扩散、自由对流和强制对流三种方式。虽然由于这些过程引起的蒸汽在变饱和地层中的运动已经建模，但由于缺乏实验室数据，必须估计传质系数。实地研究已经记录了沉积后变化的幅度，但是实地研究不允许对可能在天然积雪中起作用的许多过程的相对重要性进行严格的分析。这些实验室研究的结果将广泛适用于许多研究，并将允许改进现有的沉积后同位素变化、同位素在岩石中的扩散和岩石中的蒸汽运动的物理模型。该项目的一个主要组成部分将是设计和制造必要的、新颖的实验设备，这将由CRREL现有的技术专长、冷室设施和实验室设备来促进。该项目是定量了解大气中水蒸气运动的同位素效应的必要步骤。拟议的工作在几个不同的领域有更广泛的影响。建模结果将适用于极地环境中水的广泛研究，包括风吹雪或飘雪的研究。这项拟议中的合作研究将为达特茅斯学院的一名研究生提供三年的部分资助。该项目还将为佛蒙特大学的一名年轻的首次参与NSF研究的研究员提供支持。达特茅斯大学的本科生也将通过“女性参与科学项目”参与其中。主要研究人员和研究生将继续他们在k-12学校的传统，每年在当地学校进行科学课程和讲座。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.