Insights on muonic production of radiocarbon (14C) from ablating and accumulating ice sheets: revised production rates and improved estimates of 14C retention in firn
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Date
2021-12-16
Journal Title
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Publisher
American Geophysical Union (AGU)
Abstract
In situ cosmogenic Radiocarbon (14C) production from 16O occurs at Earth’s surface via three mechanisms: neutron-induced spallation, negative muon capture and fast muon interactions. The majority of in situ cosmogenic 14C investigations utilize the near-surface production in quartz for the determination of exposure ages where cosmogenic 14C production is dominated by spallation while near-surface muonic production represents a small correction factor in most analyses. In contrast, in situ cosmogenic 14C produced in the polar ice sheet lattice is dominated by the muonic mechanisms as a result of rapid burial from the surface in accumulation regions and extended exposure for centuries to millennia at depth before the samples are drilled and extracted from the ice sheet for analysis. Here we present two significant updates regarding the understanding of in situ cosmogenic 14C production in ice. First, measurements of ice >50ka ice 14C from Taylor Glacier are combined with an ice-flow model to find that the commonly used muogenic 14C production rates (Heisinger et al., 2002) are overestimated by factors of 5.7 (3.6-13.9, 95% CI) and 3.7 (2.0-11.9 95%CI) for negative muon capture and fast muon interactions respectively. Utilizing these revised production rates, 14C measurements of snow and ice are quantified in an ice accumulation region, finding only ~0.5% of in situ 14C is retained above the depth at which bubble closure occurs in the porous firn. Parameters are developed in a forward model to quantify the in situ cosmogenic component of accumulation zone ice core measurements and segregate them from the atmospheric component, thus expanding the utility of ice core 14C measurements for paleoclimatic reconstructions.
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Keywords
Carbon 14, Ice, Drill cores, Muon detection, Glaciers, Antarctic regions, Quartz
Citation
Hmiel, B., Dyonisius, M., Petrenko, V. V., Smith, A. M., Buizert, C., Schmitt. J., & Severinghaus, J. P. (2021). Insights on muonic production of radiocarbon (14C) from ablating and accumulating ice sheets: revised production rates and improved estimates of 14C retention in firn. Paper presented to the AGU Fall Meeting 2021, New Orleans, Louisiana and Online, 13-17 December 2021. In AGU Fall Meeting Abstracts (Vol. 2021, EP35F-1372). Retrieved from: https://agu.confex.com/agu/fm21/meetingapp.cgi/Paper/852072