Deglaciation records of &amp;lt;sup&amp;gt;17&amp;lt;/sup&amp;gt;O-excess in East Antarctica: reliable reconstruction of oceanic normalized relative humidity from coastal sites

R Winkler,A Landais,F Prié,J Jouzel,B Stenni,V Masson-Delmotte,L Dümbgen,H Sodemann

doi:10.5194/cp-8-1-2012

Abstract

Abstract. We measured δ17O and δ18O in two Antarctic ice cores at EPICA Dome C (EDC) and TALDICE (TD), respectively, and computed 17O-excess with respect to VSMOW. The comparison of our 17O-excess data with the previous record obtained at Vostok (Landais et al., 2008a) revealed differences up to 35 ppm in 17O-excess mean level and evolution for the three sites. Our data show that the large increase depicted at Vostok (20 ppm) during the last deglaciation is a regional and not a general pattern in the temporal distribution of 17O-excess in East Antarctica. The EDC data display an increase of 12 ppm, whereas the TD data show no significant variation from the Last Glacial Maximum (LGM) to the Early Holocene (EH). A Lagrangian moisture source diagnostic revealed very different source regions for Vostok and EDC compared to TD. These findings combined with the results of a sensitivity analysis, using a Rayleigh-type isotopic model, suggest that normalized relative humidity (RHn) at the oceanic source region (OSR) is a determining factor for the spatial differences of 17O-excess in East Antarctica. However, 17O-excess in remote sites of continental Antarctica (e.g. Vostok) may be highly sensitive to local effects. Hence, we consider 17O-excess in coastal East Antarctic ice cores (TD) to be more reliable as a proxy for RHn at the OSR.

Highlights

The stable isotopes 2H/H and 18O/16O ratios of water molecules in ice cores have been used for several decades as proxies for past temperature over the polar regions and have permitted the reconstruction of past climate changes over the last 800 ka in Antarctica (Jouzel et al, 2007)
Lower panel: Here we present δ18O values which were measured earlier by equilibration method; the Vostok data are from Vimeux et al (1999), while the European Project for Ice Coring in Antarctica (EPICA) Dome C (EDC) data were published by EPICA-Members (2004) and more recently the Talos Dome (TD) data by Stenni et al (2010)
We propose an explanation for the unequal mean levels of 17O-excess at Early Holocene (EH) and for the different trends over the deglaciation for the 3 sites based on the Mixed Cloud Isotopic Model (MCIM) detailed above

Summary

Introduction

The stable isotopes 2H/H and 18O/16O ratios of water molecules in ice cores have been used for several decades as proxies for past temperature over the polar regions and have permitted the reconstruction of past climate changes over the last 800 ka (ka = thousand years before present) in Antarctica (Jouzel et al, 2007). Craig and Gordon (1965) and Merlivat and Jouzel (1979) to link d-excess and conditions prevailing at the OSR, one can derive that 17O-excess and RHn of the OSR are linearly related with decreasing 17O-excess for increasing RHn This expected negative correlation has recently been monitored in situ (surface water vapour) over the Southern Ocean by Uemura et al (2010). The ice cores of EDC and TD provide both continuous and high quality information about the past climate

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Discussion

Conclusion