HR: 1340h
AN: PP33C-1592    [Abstracts]
TI: A New Method to Constrain Past Temperatures From Stable Isotope Measurements in Polar Ice, Based on Differential Smoothing of the Isotopes.
AU: * Sveinbjörnsdóttir, A E
EM: arny@raunvis.hi.is
AF: Institute of Earth Sciences, University of Iceland, Sturlugata 7, Reykjavik, IS101 Iceland
AU: Johnsen, S
EM:
AF: Institute of Earth Sciences, University of Iceland, Sturlugata 7, Reykjavik, IS101 Iceland
AU: Johnsen, S
EM:
AF: The Niels Bohr Institute, Department of Geophysics, University of Copenhagen, Juliane Maries Vej 30, Copenhagen, DK-2100 Denmark
AU: Popp, T
EM:
AF: Institute of Alpine and Arctic Research and Department of Geological Sciences, University of Colorado, 1560 30th Street, Boulder, CO 80303 United States
AU: White, J
EM:
AF: Institute of Alpine and Arctic Research and Department of Geological Sciences, University of Colorado, 1560 30th Street, Boulder, CO 80303 United States
AB: In recent years continuous and highly detailed climatic profiles from the Greenland ice sheet have been obtained for the last 120,000 years. The most frequently used proxy for past temperatures of polar ice are the measured stable isotopic values, after applying imprecise calibration. In this contribution we introduce an entirely new method to constrain past temperatures from stable isotope measurements, that has no need for calibration or imprecise corrections. Stable isotope records in polar ice are affected by diffusion both in the firn and in deeper ice as described by a quantitative theory for diffusion in firn and ice (Johnsen et al., 2000). Because of different fractionation factors, their firn theory predicts stronger smoothing for δ¹⁸O than for δ{D}. This differential smoothing opens up the possibility for using detailed isotope records to estimate paleo-temperatures in deeper strata. The precise dating of the NorthGRIP core by annual layer counting makes it possible to improve estimates of paleo-temperatures. The present project aims at constraining past temperatures and accumulation rates on the Greenland Ice Sheet (NorthGRIP and GRIP) from detailed isotopic measurements from the selected climatic periods Younger Dryas, Bölling and the Last Glacial Maximum. The method utilizes known differences that occur in the smoothing of oxygen 18 and deuterium isotope profiles during firnification. This is further seen in the different diffusion lengths for HD¹⁶O and H₂¹⁸O , which only depend on the temperature and can be estimated by using spectral methods on the measured profiles. Johnsen et al. In Physics of Ice Core Records, edited by T. Hondoh, 121-140, Hokkaido University Press, Sapporo, 2000.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005