Southern Greenland water vapour isotopic composition at the crossroads of Atlantic and Arctic moisture

Wednesday, 17 December 2014
Jean-Louis Bonne1, Hans Christian Steen-Larsen1, Camille M Risi2, Martin Werner3, Harald Sodemann4, Jean-Lionel Lacour5,6, Xavier Fettweis7, Grégory Cesana8, Marc Delmotte1, Olivier Cattani1, Cathy Clerbaux6, Arny Erla Sveinbjörnsdottir9 and Valérie Masson-Delmotte1, (1)LSCE Laboratoire des Sciences du Climat et de l'Environnement, Gif-Sur-Yvette Cedex, France, (2)LMD, Paris, France, (3)Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany, (4)ETH Zurich, Zürich, Switzerland, (5)Université Libre de Bruxelles, Brussels, Belgium, (6)UPMC Univ. Paris 06; Université Versailles St-Quentin, LATMOS-IPSL, Paris, France, (7)University of Liège, Geography, Liège, Belgium, (8)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (9)University of Iceland, Institute of Earth Sciences, Reykjavik, Iceland
Since September 2011, a continuous water vapour isotopic composition monitoring instrument has been remotely operated in Ivittuut (61.21°N, 48.17°W), southern Greenland. Meteorological parameters are monitored and precipitation has been sampled and analysed for isotopic composition, suggesting equilibrium between surface vapour and precipitation. The data depict small summer diurnal variations. δ18O and deuterium excess (d-excess) are generally anti-correlated and show important seasonal variations (with respective amplitudes of 10 and 20 ‰), and large synoptic variations associated to low-pressure systems (typically +5‰ on δ18O and −15‰ on d-excess).

The moisture sources, estimated based on Lagrangian back-trajectories, are primarily influenced by the western North Atlantic, and north-eastern American continent. Notable are important seasonal and synoptic shifts of the moisture sources, and sporadic influences of the Arctic or the eastern North Atlantic. Moisture sources variations can be related to changes in water vapour isotopic composition, and the isotopic fingerprints can be attributed to the areas of moisture origins. Isotopic enabled AGCMs nudged to meteorology (LMDZiso, ECHAM5-wiso), despite biases, correctly capture the δ18O changes, but underestimate the d-excess changes. They allow to identify a high correlation between the southern Greenland d-excess and the simulated relative humidity and d-excess in the moisture source region south of Greenland.

An extreme high temperature event in July 2012 affecting all Greenland, similar to ice sheet melt events during the medieval periods and one event in 1889 documented by Greenland ice core records, has been analysed regarding water vapour isotopic composition, using remote sensing (IASI) and in situ observations from Bermuda to northern Greenland (NEEM station). Our southern Greenland observations allow to track the water vapour evolution during this event along the moisture transport path, depicting the northward propagation of an isotopic signal inherited from the meteorological conditions during evaporation.

Overall, our observations provide valuable information for interpreting Greenland ice core records as well as for evaluating water vapour isotopic simulations in atmospheric models.