NOAA/WDS Paleoclimatology - GISP2 Ice Core 1000 Year Ar-N2 Isotope Temperature Reconstruction

STUDY NOTES: Nitrogen and Argon isotope data from air bubbles in the GISP2 ice core, and 1000 year temperature reconstruction based on the gas isotope data. Nitrogen (15N/14N) and argon (40Ar/36Ar) isotopic ratios were measured, and a firn air separation model was used to reconstruct decadally averaged surface temperature. The thickness of the firn layer and the temperature gradient between the top and bottom of the firn layer causes known amounts of isotopic separation by gravitational and thermal fractionation, respectively (Severinghaus et al. 1998). Measurements of two isotopic ratios with differing sensitivity (d15N and d40Ar) allow separation of the two effects, providing the past firn thickness and temperature gradient DT (Kobashi et al. 2007, 2008a, b; Severinghaus and Brook 1999). Surface temperature can be calculated from the DT and accumulation rate data (Kobashi et al. 2008a), combined with a firn-densification/heat diffusion model.
ABSTRACT SUPPLIED BY ORIGINATOR: Future Greenland temperature evolution will affect melting of the ice sheet and associated global sea-level change. Therefore, understanding Greenland temperature variability and its relation to global trends is critical. Here, we reconstruct the last 1,000 years of central Greenland surface temperature from isotopes of N2 and Ar in air bubbles in an ice core. This technique provides constraints on decadal to centennial temperature fluctuations. We found that northern hemisphere temperature and Greenland temperature changed synchronously at periods of ~20 years and 40-100 years. This quasi-periodic multi-decadal temperature fluctuation persisted throughout the last millennium, and is likely to continue into the future.