NorthGRIP firn temperature reconstruction based on water isotope firn diffusion

In this study we look into the water isotope diffusion history as estimated by the spectral characteristics of the d18O time series covering the last 16,000 years. The diffusion of water vapor in the porous medium of the firn pack attenuates the initial isotopic signal, predominantly having an impact on the high frequency components of the power spectrum.

Higher temperatures induce higher rates of smoothing and thus the signal can be used as a firn paleothermometer. We use a water isotope diffusion model coupled to a steady-state densification model in order to infer the temperature signal from the site, assuming the accumulation and strain rate history as estimated using the GICC05 layer counted chronology and a Dansgaard-Johnsen ice flow model. The temperature reconstruction accurately captures the timing and magnitude of the Bølling-Allerød and Younger Dryas transitions.