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

Michael N. Dyonisius, Vasilii V. Petrenko, Andrew M. Smith, Benjamin Hmiel, Peter D. Neff, Bin Yang, Quan Hua, Jochen Schmitt, Sarah A. Shackleton, Christo Buizert, Philip F. Place, James A. Menking, Ross Beaudette, Christina Harth, Michael Kalk, Heidi A. Roop, Bernhard Bereiter, Casey Armanetti, Isaac Vimont, Sylvia Englund MichelEdward J. Brook, Jeffrey P. Severinghaus, Ray F. Weiss, Joseph R. McConnell

Research output: Contribution to journalArticlepeer-review

Abstract

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 (16O) in minerals such as ice and quartz can produce carbon-14 (14C). 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 >6gm solid ice equivalent) are uncertain. In this study, we use measurements of in situ 14C in ancient ice (>50gka) 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 14C production by muons and the partitioning of in situ 14C between CO2, CO, and CH4. Our measurements show that 33.7g% (±11.4%; 95g% confidence interval) of the produced cosmogenic 14C forms 14CO and 66.1g% (±11.5%; 95g% confidence interval) of the produced cosmogenic 14C forms 14CO2. 14CH4 represents a very small fraction (<0.3%) of the total. Assuming that the majority of in situ muogenic 14C in ice forms 14CO2, 14CO, and 14CH4, we also calculated muogenic 14C production rates that are lower by factors of 5.7 (3.6-13.9; 95g% confidence interval) and 3.7 (2.0-11.9; 95g% 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 14C production rates in ice and quartz currently lacks a good explanation and requires further investigation.

Original languageEnglish (US)
Pages (from-to)843-863
Number of pages21
JournalCryosphere
Volume17
Issue number2
DOIs
StatePublished - Feb 20 2023

Bibliographical note

Funding Information:
This research has been supported by the Office of Polar Programs (grant nos. PLR-1245659, PLR-1245821, and PLR-1246148).

Funding Information:
We thank Mike Jayred of the U.S. Ice Drilling Program (IDP), for ice drilling, camp manager Kathy Schroeder, for assistance in the field, and the United States Antarctic Program (USAP), for logistical support. We thank Emily Mesiti, for her assistance in the Rochester ice core lab during the sublimation extraction campaign. This work has been supported by the U.S. NSF awards (grant nos. PLR-1245659 for VVP, PLR-1245821 for EJB, and PLR-1246148 for JPS) and the Packard Fellowship for Science and Engineering (VVP).

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