Measurements of cosmic-ray-produced 14 C in firn and ice from antarctica

• Main Authors: Timothy Jull, A. J., Lal, Devendra, Donahue, Douglas J., Mayewski, P., Lorius, C., Raynaud, D., Petit, J. R.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier Science 1994
• Subjects: QE Geology; Newall; Newall Glacier; Antarc*; Antarctica
• Online Access: http://repository.ias.ac.in/19249/; http://linkinghub.elsevier.com/retrieve/pii/0168583X94960283

We have studied the levels of 14 C in firn and ice from two regions accumulating ice in Antarctica, Dome C, and Newall Glacier. The observed concentrations indicate variable amounts of in-situ 14 C from cosmic-ray spallation of oxygen. 14 C appears to be produced as both CO and CO 2 in variable amounts, but our results suggest rapid conversion of 14 CO to 14 CO 2 . Much of the in-situ 14 C is retained which results in a significant modification of the 14 C/ 12 C in ice derived from trapping of air at and below the firn-ice transition zone. This means that direct dating of accumulating ice cannot be used without correction for the in-situ 14 C. In Newall ice, we see some evidence for an enhancement in in-situ 14 C at or near the time of the Maunder Minimum. Results for Dome C firn and ice indicate higher levels of in-situ 14 C in older ice. This is due either to a reduced accumulation rate in the past, or possible variations in cosmogenic 14 C production. The levels of in-situ 14 C in firn and ice, and its impact on 14 C dates on trapped CO 2 in ice are discussed.