On determining ice accumulation rates in the past 40 000 years using in situ cosmogenic 14C

D. Lal, A. J T Jull

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Radiocarbon is produced in situ in ice by nuclear spallations of oxygen by cosmic ray neutrons. As the firn accumulates, it acquires a predictable concentration of in situ 14C, inversely proportional to the rate of accumulation. Most of this production occurs when the amount of overlying ice is less than (2-3) Λ, where Λ is the absorption mean free path for cosmic radiation in ice, about 150 g.cm-2, i.e. within the top 10 m. In most accumulation areas, this is firn. In situ produced 14C is added to the firn as it accumulates, and is not expected to be lost by diffusion. During the firn-ice transition, atmospheric CO2 is trapped, adding 14CO2 to the ice. The signature of in situ 14C is however not obliterated. We discuss the results available to date and propose that this in situ 14CO can be used to determine ice accumulation rates back to 40 000 yrs in the past. -from Authors

Original languageEnglish (US)
Pages (from-to)1303-1306
Number of pages4
JournalGeophysical Research Letters
Volume17
Issue number9
StatePublished - 1990

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accumulation rate
ice
firn
cosmic rays
spallation
mean free path
cosmic ray
in situ
signatures
neutrons
oxygen

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)

Cite this

On determining ice accumulation rates in the past 40 000 years using in situ cosmogenic 14C. / Lal, D.; Jull, A. J T.

In: Geophysical Research Letters, Vol. 17, No. 9, 1990, p. 1303-1306.

Research output: Contribution to journalArticle

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AB - Radiocarbon is produced in situ in ice by nuclear spallations of oxygen by cosmic ray neutrons. As the firn accumulates, it acquires a predictable concentration of in situ 14C, inversely proportional to the rate of accumulation. Most of this production occurs when the amount of overlying ice is less than (2-3) Λ, where Λ is the absorption mean free path for cosmic radiation in ice, about 150 g.cm-2, i.e. within the top 10 m. In most accumulation areas, this is firn. In situ produced 14C is added to the firn as it accumulates, and is not expected to be lost by diffusion. During the firn-ice transition, atmospheric CO2 is trapped, adding 14CO2 to the ice. The signature of in situ 14C is however not obliterated. We discuss the results available to date and propose that this in situ 14CO can be used to determine ice accumulation rates back to 40 000 yrs in the past. -from Authors

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