Clim. Past Discuss., 9, 6035-6076, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
What controls the isotopic composition of Greenland surface snow?
H. C. Steen-Larsen1,2,3, V. Masson-Delmotte1, M. Hirabayashi4, R. Winkler1, K. Satow4, F. Prié1, N. Bayou2, E. Brun5, K. M. Cuffey6, D. Dahl-Jensen3, M. Dumont7, M. Guillevic1,3, J. Kipfstuhl8, A. Landais1, T. Popp3, C. Risi9, K. Steffen2,10, B. Stenni11, and A. Sveinbjörnsdottír12
1Laboratoire des Sciences du Climat et de l'Environnement, UMR8212, CEA-CNRS-UVSQ/IPSL, Gif-sur-Yvette, France
2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, USA
3Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Denmark
4National Institute of Polar Research, Tokyo, Japan
5Meteo-France – CNRS, CNRM-GAME UMR 3589, GMGEC, Toulouse, France
6Department of Geography, Center for Atmospheric Sciences, 507 McCone Hall, University of California, Berkeley, Berkeley, CA 94720-4740, USA
7Meteo-France – CNRS, CNRM-GAME UMR 3589, CEN, Grenoble, France
8Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
9Laboratoire de Meìteìorologie Dynamique, Jussieu, Paris, France
10ETH, Swiss Federal Institute of Technology, Zurich, Switzerland
11Department of Geological, Environmental and Marine Sciences, University of Trieste, Italy
12Institute of Earth Sciences, University of Iceland, Reykjavik, Iceland

Abstract. Water stable isotopes in Greenland ice core data provide key paleoclimatic information, and have been compared with precipitation isotopic composition simulated by isotopically-enabled atmospheric models. However, post-deposition processes linked with snow metamorphism remain poorly documented. For this purpose, a monitoring of the isotopic composition (δ18O, δD) of surface water vapor, precipitation and samples of top (0.5 cm) snow surface has been conducted during two summers (2011–2012) at NEEM, NW Greenland. The measurements also include a subset of 17O-excess measurements over 4 days, and the measurements span the 2012 Greenland heat wave. Our observations are consistent with calculations assuming isotopic equilibrium between surface snow and water vapor. We observe a strong correlation between surface vapor δ18O and air temperature (0.85 ± 0.11 ‰ °C−1 (R = 0.76) for 2012). The correlation with air temperature is not observed in precipitation data or surface snow data. Deuterium excess (d-excess) is strongly anti-correlated with δ18O with a stronger slope for vapor than for precipitation and snow surface data. During nine 1–5 days periods between precipitation events, our data demonstrate parallel changes of δ18O and d-excess in surface snow and surface vapor. The changes in δ18O of the vapor are similar or larger than those of the snow δ18O. It is estimated that 6 to 20% of the surface snow mass is exchanged with the atmosphere using the CROCUS snow model. In our data, the sign of surface snow isotopic changes is not related to the sign or magnitude of sublimation or condensation. Comparisons with atmospheric models show that day-to-day variations in surface vapor isotopic composition are driven by synoptic weather and changes in air mass trajectories and distillation histories. We suggest that, in-between precipitation events, changes in the surface snow isotopic composition are driven by these changes in surface vapor isotopic composition. This is consistent with an estimated 60% mass turnover of surface snow per day driven by snow recrystallization processes under NEEM summer surface snow temperature gradients. Our findings have implications for ice core data interpretation and model-data comparisons, and call for further process studies.

Citation: Steen-Larsen, H. C., Masson-Delmotte, V., Hirabayashi, M., Winkler, R., Satow, K., Prié, F., Bayou, N., Brun, E., Cuffey, K. M., Dahl-Jensen, D., Dumont, M., Guillevic, M., Kipfstuhl, J., Landais, A., Popp, T., Risi, C., Steffen, K., Stenni, B., and Sveinbjörnsdottír, A.: What controls the isotopic composition of Greenland surface snow?, Clim. Past Discuss., 9, 6035-6076, doi:10.5194/cpd-9-6035-2013, 2013.
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