Greenland temperature is one of the most important variables when considering future climate change, as it has the potential to impact a significant percentage of the population through an increase of the global sea level resulting from the melting of the Greenland ice sheet. Therefore, it is critical to understand the mechanism of Greenland temperature variability over multidecadal to centennial time scales with societal relevance. A new method has been developed to reconstruct Greenland temperature variability using argon and nitrogen isotopes in occluded air in ice cores coupled with a firn densification heat diffusion model. The method is based upon the fact that gasses in the firn (unconsolidated snow layer) fractionate based on the depth and temperature gradient of the layer. In the proposed research, we plan to reconstruct temperature change in northern Greenland over the past 6000 years using the NGRIP ice core. The period from the middle Holocene to the present is considered similar to the preindustrial climate, so it is an important period for which to understand the natural climate variability because the future climate under increasing greenhouse gasses is expected to evolve with the natural variability. The NGRIP ice core will be analysed for the argon and nitrogen isotopes of occluded air in ice cores, and the firn densification models used to calculate the surface temperature will be improved by testing them with other models and data from other cores. A new firn model that is fully consistent with argon and nitrogen isotopes, the Ar/N2 ratio in occluded air, and the oxygen isotopes of ice will then be developed, which may provide information on past accumulation rate change. Finally, the reconstructed Greenland temperature changes will be investigated with climate models to constrain the past influences of North Atlantic Oscillation and Atlantic meridional overturning circulation.
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