Using ice core measurements from Taylor Glacier, Antarctica, to calibrate in situ cosmogenic 14 C production rates by muons

• Published in: The Cryosphere
• Main Authors: M. N. Dyonisius, V. V. Petrenko, A. M. Smith, B. Hmiel, P. D. Neff, B. Yang, Q. Hua, J. Schmitt, S. A. Shackleton, C. Buizert, P. F. Place, J. A. Menking, R. Beaudette, C. Harth, M. Kalk, H. A. Roop, B. Bereiter, C. Armanetti, I. Vimont, S. Englund Michel, E. J. Brook, J. P. Severinghaus, R. F. Weiss, J. R. McConnell
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: Environmental sciences; GE1-350; Geology; QE1-996.5; Taylor Glacier; Antarc*; Antarctica; ice core; The Cryosphere
• Online Access: https://doi.org/10.5194/tc-17-843-2023; https://doaj.org/article/07c7e30c42454b0aa85d33a5ab319094

Cosmic rays entering the Earth's atmosphere produce showers of secondary particles such as protons, neutrons, and muons. The interaction of these particles with oxygen-16 ( 16 O ) in minerals such as ice and quartz can produce carbon-14 ( 14 C ). In glacial ice, 14 C is also incorporated through trapping of 14 C -containing atmospheric gases ( 14 CO 2 , 14 CO , and 14 CH 4 ). Understanding the production rates of in situ cosmogenic 14 C is important to deconvolve the in situ cosmogenic and atmospheric 14 C signals in ice, both of which contain valuable paleoenvironmental information. Unfortunately, the in situ 14 C production rates by muons (which are the dominant production mechanism at depths of >6 m solid ice equivalent) are uncertain. In this study, we use measurements of in situ 14 C in ancient ice ( >50 ka) from the Taylor Glacier, an ablation site in Antarctica, in combination with a 2D ice flow model to better constrain the compound-specific rates of 14 C production by muons and the partitioning of in situ 14 C between CO 2 , CO, and CH 4 . Our measurements show that 33.7 % ( ±11.4 % 95 % confidence interval) of the produced cosmogenic 14 C forms 14 CO and 66.1 % ( ±11.5 % 95 % confidence interval) of the produced cosmogenic 14 C forms 14 CO 2 . 14 CH 4 represents a very small fraction ( <0.3 % ) of the total. Assuming that the majority of in situ muogenic 14 C in ice forms 14 CO 2 , 14 CO , and 14 CH 4 , we also calculated muogenic 14 C production rates that are lower by factors of 5.7 (3.6–13.9; 95 % confidence interval) and 3.7 (2.0–11.9; 95 % confidence interval) for negative muon capture and fast muon interactions, respectively, when compared to values determined in quartz from laboratory studies (Heisinger et al., 2002a, b) and in a natural setting (Lupker et al., 2015). This apparent discrepancy in muogenic 14 C production rates in ice and quartz currently lacks a good explanation and requires further investigation.