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

• Published in: The Cryosphere
• Main Authors: Dyonisius, Michael N., Petrenko, Vasilii V., Smith, Andrew M., Hmiel, Benjamin, Neff, Peter D., Yang, Bin, Hua, Quan, Schmitt, Jochen, Shackleton, Sarah A., Buizert, Christo, Place, Philip F., Menking, James A., Beaudette, Ross, Harth, Christina, Kalk, Michael, Roop, Heidi A., Bereiter, Bernhard, Armanetti, Casey, Vimont, Isaac, Englund Michel, Sylvia, Brook, Edward J., Severinghaus, Jeffrey P., Weiss, Ray F., McConnell, Joseph R.
• Format: Text
• Language: English
• Published: 2023
• Subjects: Taylor Glacier; Antarc*; Antarctica; ice core
• Online Access: https://doi.org/10.5194/tc-17-843-2023; https://tc.copernicus.org/articles/17/843/2023/

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.