Collaborative Research: Investigating the potential of carbon-14 in polar firn and ice as a tracer of past cosmic ray flux and an absolute dating tool

拟议的工作将调查冰芯中的碳-14作为绝对测年工具、作为过去宇宙射线通量的示踪剂和作为全球甲烷收支中过去化石部分的记录器的潜力。宇宙射线粒子直接在近地表的冰川和积雪中从氧-16产生碳-14。这种原位产生的碳-14迅速反应，在冰基质中形成含14 C的二氧化碳、一氧化碳和甲烷。部分或全部含14 C的气体可能会从雪中流失到大气中。拟议的工作将提供一个彻底的特点，在格陵兰岛的首脑会议地区的冰川积雪和浅冰在原地宇宙成因14 C。它将研究在所有深度水平的冰粒中宇宙成因14 C的保留在雪柱中，二氧化碳，一氧化碳和甲烷之间的14 C的分配，以及宇宙成因14 C在雪关闭以下的浅冰中的生产率和积累。对雪和浅冰中宇宙成因的C-14的透彻理解将可能使冰中的C-14用于以下一种或多种应用：1）如果在气泡被封闭的深度以下的冰中存在相对大量的宇宙成因的14 C，它将用作过去宇宙射线通量的示踪剂。调查人员认为，这可能是14 C-一氧化碳的情况。2)如果与滞留空气中的14 C-二氧化碳相比，原地产生的14 C-二氧化碳的保留量相对较小，则研究将证明使用14 C-二氧化碳对冰芯进行绝对定年的有效性;这长期以来一直是冰芯研究的目标。3）如果原位产生的14 C-甲烷的保留量与来自截留空气的14 C-甲烷相比相对较小，这项研究将证明利用冰川冰中的14 C-甲烷来确定过去甲烷收支中化石部分的有效性，包括甲烷包合物的释放。2这项拟议的工作将在罗切斯特大学（UR）和伯尔尼大学之间建立一个新的国际合作，并产生新的实验室和现场分析系统。研究数据将通过ACADIS数据服务提供给科学界和广大公众。一名研究生将在UR接受培训，一名博士后和一名研究生将在俄勒冈州州立大学获得部分支持。三个UR本科生将参与实地考察和研究。这项工作将支持一个早期的职业科学家。所有调查人员将继续参加公共宣传活动。

The proposed work will investigate the potential of carbon-14 in ice cores as an absolute dating tool, as a tracer of the past cosmic ray flux and as a recorder of the past fossil fraction of the global methane budget. Cosmic ray particles produce carbon-14 from oxygen-16 directly within near-surface glacial ice and firn. This in-situ produced carbon-14 quickly reacts to form 14C-containing carbon dioxide, carbon monoxide, and methane in the ice matrix. Some or all of the resulting 14C-bearing gases may be lost from the firn to the atmosphere. The proposed work will provide a thorough characterization of in-situ cosmogenic 14C in glacial firn and shallow ice in the Summit region of Greenland. It will examine the retention of cosmogenic 14C in ice grains at all depth levels in the firn column, the partitioning of 14C between carbon dioxide, carbon monoxide, and methane, as well as the production rates and accumulation of cosmogenic 14C in shallow ice below firn close-off. A thorough understanding of cosmogenic C-14 in firn and shallow ice will likely enable the use of C-14 in ice for one or more of the following applications:
1) If a relatively large amount of cosmogenic 14C is present in ice below the depth at which air bubbles become sealed off, it will be useful as a tracer for past cosmic ray flux. The investigators believe that this is the likely case for 14C-carbon monoxide. 2) If the amount of retained in-situ-produced 14C-carbon dioxide is relatively small compared to 14C-carbon dioxide from trapped air, the study will demonstrate the validity of using 14C-carbon dioxide for absolute dating of ice cores; this has long been a target of ice core studies.3) If the amount of retained in-situ-produced 14C-methane is relatively small compared to 14C-methane from trapped air, the study will demonstrate the validity of using 14C-methane in glacial ice for determinations of the fossil fraction of the past methane budget, including releases from methane clathrates.The proposed work will establish a new international collaboration between University of Rochester (UR) and University of Bern and result in novel laboratory and field analytical systems. The data from the study will be made available to the scientific community and the broad public through the ACADIS data service. One graduate student will be trained at UR, and one postdoc and one graduate student will be partially supported at Oregon State University. Three UR undergraduates will be involved in fieldwork and research. The work will support an early career scientist. All of the investigators will continue to participate in public outreach.