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

Abstract

Abstract. Cosmic rays entering the Earth’s atmosphere produce showers of secondary particles such as neutrons and muons. The interaction of these neutrons and muons with oxygen-16 (16O) in minerals such as ice and quartz can produce carbon-14 (14C). Analyses of in situ produced cosmogenic 14C in quartz are commonly used to investigate the Earth’s landscape evolution. In glacial ice, 14C is also incorporated through trapping of 14C-containing atmospheric gases (14CO2, 14CO, and 14CH4). Understanding the production rates of in situ cosmogenic 14C is important to deconvolve the in situ cosmogenic and atmospheric 14C signals in ice, both of which contain valuable paleoenvironmental information. Unfortunately, the in situ 14C 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 14C in ancient ice (> 50 kilo-annum before present, ka BP) from the Taylor Glacier ablation site, Antarctica in combination with a 2D ice flow model to better constrain the rates of 14C production by muons. We find that the commonly used values for muogenic 14C production rates (Heisinger et al., 2002a, 2002b) in ice are too high 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. Our constraints on muogenic 14C production rates in ice allow for future measurements of 14C in ice cores to be used for other applications and imply that muogenic 14C production rates in quartz are overestimated as well.