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

点击翻译按钮获取中文摘要

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.