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- Title
Past surface temperatures at the NorthGRIP drill site from the difference in firn diffusion of water isotopes.
- Authors
Simonsen, S. B.; Johnsen, S. J.; Popp, T. J.; Vinther, B. M.; Gkinis, V.; Steen-Larsen, H. C.
- Abstract
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 isotopes 18O and deuterium. 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 resulting in a longer diffusion length than by assuming an isothermal firn. The longer diffusion length can be explained by the strong non-linearly behavior of the saturation pressure over ice in the range of the surface temperature fluctuations. The method has been tested on δ18O and ~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 Allerød warming is seen to be significantly warmer than observed in other ice core based temperature reconstructions. The mechanisms behind this behavior are not fully understood. The method shows the need of an expansion of high resolution stable water isotopes data sets from ice cores. However, the new ice core paleothermometer presented here will give valuable insight in past climate, through the physical process of isotope diffusion in the firn column of ice sheets.
- Subjects
PALEOTHERMOMETRY; ICE cores; WATER; ISOTOPES; DIFFUSION; ISOTHERMAL surfaces (Thermodynamics); DRILLING &; boring
- Publication
Climate of the Past Discussions, 2011, Vol 7, Issue 2, p921
- ISSN
1814-9324
- Publication type
Article
- DOI
10.5194/cpd-7-921-2011