Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 105, Issue 24, Pages 8232-8237Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0711679105
Keywords
geochronology; ice cores; geodynamics; noble gases
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Knowledge of the outgassing history of radiogenic Ar-40, derived over geologic time from the radioactive decay of K-40, contributes to our understanding of the geodynamic history of the planet and the origin of volatiles on Earth's surface. The Ar-40 inventory of the atmosphere equals total Ar-40 outgassing during Earth history. Here, we report the current rate of Ar-40 outgassing, accessed by measuring the Ar isotope composition of trapped gases in samples of the Vostok and Dome C deep ice cores dating back to almost 800 ka. The modern outgassing rate (1.1 +/- 0.1 x 10(8) mol/yr) is in the range of values expected by summing outgassing from the continental crust and the upper mantle, as estimated from simple calculations and models. The measured outgassing rate is also of interest because it allows dating of air trapped in ancient ice core samples of unknown age, although uncertainties are large (+/- 180 kyr for a single sample or +/- 11% of the calculated age, whichever is greater).
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