Past surface temperatures at the NorthGRIP drill site from the difference in firn diffusion of water isotopes

Sebastian Bjerregaard Simonsen, S. J. Johnsen, T. J. Popp, B. M. Vinther, V. Gkinis, H. C. Steen-Larsen

Research output: Contribution to journalJournal articleResearchpeer-review

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 isotopologues 2H1H16O and 1H218O. 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 δ18O and δD 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 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. © Author(s) 2011.

Original languageEnglish
JournalClimate of the Past
Volume7
Issue number4
Pages (from-to)1327-1335
ISSN1814-9324
DOIs
Publication statusPublished - 2011
Externally publishedYes

Keywords

  • Geosciences
  • Meteorology
  • Abrupt climate-change
  • Last glacial termination
  • Ice core chronology
  • Stable-isotopes
  • Camp century
  • Polar ice
  • Greenland
  • Atlantic
  • Record
  • Grip

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