Cosmogenic Carbon-14 In Glacial Firn and Ice

Cosmic rays, originating primarily outside of our solar system, are constantly bombarding the Earth. These energetic charged particles induce nuclear reactions in the Earth’s atmosphere and at the surface. One of the products of these reactions is carbon-14 (¹⁴C), the radioactive isotope of carbon commonly used for radiometric dating. Carbon-14 is produced in the atmosphere from nitrogen-14, and is responsible for the ¹⁴C content of atmospheric carbon dioxide (CO₂), carbon monoxide (CO) and methane (CH₄). ¹⁴C is also produced by cosmic rays directly in snow and glacial ice from oxygen-16. This new 14C rapidly reacts with O and H atoms in the ice to form CO, CO₂ as well as smaller amounts of CH4.The amount of ¹⁴CO, ¹⁴CO₂ and ¹⁴CH₄ found in glacial ice cores is therefore determined by a combination of ¹⁴C included with atmospheric gases trapped in the air bubbles in the ice and ¹⁴C produced directly in the ice by cosmic rays. Ice core reconstructions of  ¹⁴C content of past atmospheric CH₄ can tell us about changes in natural methane emissions and their response to climate. ¹⁴C of CO₂ in old air trapped in ice cores could be used for establishing the age of this ancient air. ¹⁴C of CO in glacial ice is a promising tracer of the past cosmic ray flux, as well as of the past atmospheric oxidizing capacity. However, to use any of these tracers in a meaningful way, we need to be able to distinguish between the ¹⁴C that was included in the ice with trapped air and ¹⁴C that was produced directly in the ice by cosmic rays.

Our group’s projects at Summit, Greenland and Taylor Glacier, Antarctica aim to understand the rates at which  ¹⁴C is produced in ice at different depths, as well as how much of this ¹⁴C stays in the ice and how much escapes to the atmosphere from the thick snowpack that forms the upper layer of ice sheets. We are also hoping to initiate a new project at Dome C, Antarctica, which would use ¹⁴CO in ice cores at this very cold, low-snow-accumulation site to examine past variations in the flux of galactic cosmic rays for the last few thousand years.

   This project has been supported by the Packard Foundation and by NSF Polar awards ARC-1203779 and PLR-1245659

Related Publications

Dyonisius, M., Petrenko, V., Smith, A., Hmiel, B., Neff, P., Yang, B., Hua, Q., Schmitt, J., Shackleton, S., Buizert, C., Place, P., Menking, J., Beaudette, R., Harth, C., Kalk, M., Roop, H., Bereiter, B., Armanetti, C., Vimont, I., Michel, S. E., Brook, E., Severinghaus , J., Weiss, R., McConnell, J. 2022. Using ice core measurements from Taylor Glacier, Antarctica to calibrate in situ cosmogenic  14 C production rates by muons. The Cryosphere Discussions, https://doi.org/10.5194/tc-2021-375.

BenZvi, S., V.V. Petrenko, B. Hmiel, M. Dyonisius, A.M. Smith, B. Yang, Q. Hua. Obtaining a History of the Flux of Cosmic Rays using In Situ Cosmogenic 14 C Trapped in Polar Ice. Proceedings of the 36th International Cosmic Ray Conference - ICRC2019. https://arxiv.org/abs/1909.07994.

Buizert, C., V.V. Petrenko, J. L. Kavanaugh, K.M. Cuffey, N.A. Lifton, E.J. Brook, J.P. Severinghaus. 2012. In-situ cosmogenic radiocarbon production and 2-D ice flow line modeling for an Antarctic blue ice area. Journal of Geophysical Research – Earth Surface, 117, F02029, doi:10.1029/2011JF002086. http://onlinelibrary.wiley.com/doi/10.1029/2011JF002086/full 

Petrenko, V.V.. J. Severinghaus, A.M. Smith, K. Riedel, D. Baggenstos, C. Harth, A. Orsi, Q. Hua, P. Franz, Y. Takeshita, G. Brailsford, R.F. Weiss, C. Buizert, A. Dickson, and H. Schaefer. High-precision ¹⁴C measurements demonstrate production of in situ cosmogenic ¹⁴CH₄ and rapid loss of in situ cosmogenic ¹⁴CO in shallow Greenland firn. 2013. Earth and Planetary Science Letters, 365, 190-197. http://www.sciencedirect.com/science/article/pii/S0012821X13000496

Petrenko, V.V., J.P. Severinghaus, H. Schaefer, A.M. Smith, T. Kuhl, D. Baggenstos, Q. Hua, E.J. Brook, P. Rose, R. Kulin, T. Bauska, C. Harth, C. Buizert, A. Orsi, G. Emanuele, J. E. Lee, G. Brailsford, R. Keeling, R.F. Weiss. 2016. Measurements of ¹⁴C in ancient ice from Taylor Glacier, Antarctica constrain in situ cosmogenic ¹⁴CH₄ and ¹⁴CO production rates. Geochimica et Cosmochimica Acta, 177, 62 – 77. http://www.sciencedirect.com/science/article/pii/S0016703716000065