Journal
CLIMATE OF THE PAST
Volume 7, Issue 4, Pages 1327-1335Publisher
COPERNICUS GESELLSCHAFT MBH
DOI: 10.5194/cp-7-1327-2011
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Funding
- FNU in Denmark
- FNRS-CFB in Belgium
- IPEV in France
- INSU/CNRS in France
- AWI in Germany
- RannIs in Iceland
- MEXT in Japan
- SPRS in Sweden
- SNF in Switzerland
- NSF, Office of Polar Programs in USA
- National Science Foundation
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A new ice core paleothermometer is introduced based on the temperature dependent diffusion of the stable water isotopes in the firn. A new parameter called differential diffusion length is defined as the difference between the diffusion length of the two stable water isotopologues (HHO)-H-2-H-1-O-16 and (H2O)-H-1-O-18. A model treatment of the diffusion process of the firn and the ice is presented along with a method of retrieving the diffusion signal from the ice core record of water isotopes using spectral methods. The model shows how the diffusion process is highly dependent on the inter-annual variations in the surface temperatures. It results in a diffusion length longer than if the firn was isothermal. The longer diffusion length can be explained by the strong nonlinearly behaviour of the saturation pressure over ice in the range of the surface temperature fluctuations. The method has been tested on delta O-18 and delta D measurements, spanning the transition from the last glacial to the holocene, from the NorthGRIP ice core. The surface temperature reconstruction based on the differential diffusion resembles other temperature reconstructions for the NorthGRIP ice core. However, the Allerod warming is seen to be significantly warmer than observed in other ice core based temperature reconstructions. The mechanisms behind this behaviour are not fully understood. The method shows the need of an expansion of high resolution stable water isotope datasets from ice cores. However, the new ice core paleothermometer presented here will give valuable insight into past climate, through the physical process of isotope diffusion in the firn column of ice sheets.
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