Gravitational Enrichment of ^(84)Kr/^(36)Ar Ratios in Polar Ice Caps: A Measure of Firn Thickness and Accumulation Temperature
- Creators
- Craig, H.
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Wiens, R. C.
Abstract
Measurements of ^(84)Kr/^(36)Ar ratios in Greenland ice show that gravitational separation in the firn layer is responsible for the enrichments relative to atmospheric ratios. The ^(84)Kr/^(36)Ar ratio is enriched by 12.8 per mil and is 24 times the ^(18)O/^(16)O enrichment in trapped O_2, as predicted for gravitational fractionation. Because gravitational enrichment depends on firn thickness, which in turn depends on annual mean temperature, noble gas ratios provide a method for determining paleotemperatures and ancient firn thicknesses in polar ice caps. The gravitational effects are modulated by about 10 to 15 percent by atmospheric concentration changes caused by temperature effects on oceanic gas solubilities. The availability of five noble gases should make it possible to deconvolute the solubility and gravitational enrichments for calibration of ^(18)O paleotemperatures throughout the polar ice sheets.
Additional Information
© 1996 American Association for the Advancement of Science Received 13 July 1995; accepted 17 January 1996. We thank J. Welhan and the members of the PICO group for drilling the Dye 3 ice core, D. Burtner for laboratory assistance, K. Turekian for discussion, and C. C. Langway Jr. for his interest in and enthusiasm for our ice-core work. R. Keeling pointed out to us that atmospheric concentrations will be affected by global temperature changes. Supported by the Polar Programs Office of NSF.Additional details
- Alternative title
- Gravitational Enrichment of 84Kr/36Ar Ratios in Polar Ice Caps: A Measure of Firn Thickness and Accumulation Temperature
- Eprint ID
- 52842
- DOI
- 10.1126/science.271.5256.1708
- Resolver ID
- CaltechAUTHORS:20141216-082509059
- NSF
- Created
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2014-12-16Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field