Greenland Water Vapour and Precipitation Isotopic Composition
Total Page:16
File Type:pdf, Size:1020Kb
Open Access Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Atmos. Chem. Phys. Discuss., 13, 30521–30574, 2013 Atmospheric www.atmos-chem-phys-discuss.net/13/30521/2013/ Chemistry doi:10.5194/acpd-13-30521-2013 ACPD © Author(s) 2013. CC Attribution 3.0 License. and Physics Discussions 13, 30521–30574, 2013 This discussion paper is/has been under review for the journal Atmospheric Chemistry Greenland water and Physics (ACP). Please refer to the corresponding final paper in ACP if available. vapour and precipitation isotopic The isotopic composition of water vapour composition and precipitation in Ivittuut, Southern J.-L. Bonne et al. Greenland Title Page 1 1 1 1 3 J.-L. Bonne , V. Masson-Delmotte , O. Cattani , M. Delmotte , C. Risi , Abstract Introduction H. Sodemann2, and H. C. Steen-Larsen1 Conclusions References 1Laboratoire des Sciences du Climat et de l’Environnement, UMR8212, Gif sur Yvette, France 2Institute For Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland Tables Figures 3Laboratoire de Météorologie Dynamique, Paris, France J I Received: 14 October 2013 – Accepted: 4 November 2013 – Published: 21 November 2013 Correspondence to: J.-L. Bonne ([email protected]) J I Published by Copernicus Publications on behalf of the European Geosciences Union. Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 30521 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract ACPD Since September 2011, a Wavelength-Scanned Cavity Ringdown Spectroscopy ana- lyzer has been remotely operated in Ivittuut, southern Greenland, providing the first 13, 30521–30574, 2013 continuous record of surface water vapour isotopic composition (δ18O, δD) in South 5 Greenland and the first record including the winter season in Greenland. This record Greenland water depicts small summer diurnal variations. Measurements of precipitation isotopic com- vapour and position suggest equilibrium between surface vapour and precipitation. precipitation isotopic The vapour data show large synoptic and seasonal variations corresponding to shifts composition in moisture sources estimated using a quantitative moisture source diagnostic. The 18 10 arrival of low pressure systems towards south Greenland leads to δ O enrichment J.-L. Bonne et al. (+5 ‰) and deuterium excess depletion (−15 ‰), coupled with moisture sources shifts. Monthly δ18O is minimum in November–December and maximum in June–July, with a seasonal amplitude of ∼ 10 ‰. The strong correlation between δ18O and the loga- Title Page rithm of local surface humidity is consistent with Rayleigh distillation processes. The re- Abstract Introduction ◦ −1 15 lationship with local surface air temperature is associated with a slope of ∼0.4 ‰ C . During the summer 2012 heat waves, the observations display a divergence between Conclusions References δ18O and local climate variables, probably due to the isotopic depletion associated with Tables Figures long distance transport from subtropical moisture sources. Monthly deuterium excess is minimum in May–June and maximum in November, with 18 J I 20 a seasonal amplitude of 20 ‰. It is anti-correlated with δ O, and correlated with local surface relative humidity (at the station) as well as surface relative humidity in a North J I Atlantic sector, south of Greenland and Iceland. While synoptic and seasonal variations are well represented by the Atmospheric Back Close 18 General Circulation Model LMDZiso for Ivittuut δ O, the model does not capture the Full Screen / Esc 25 magnitude of these variations for deuterium excess. Printer-friendly Version Interactive Discussion 30522 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 Introduction 18 ACPD Water stable isotopologues (H2O, H2 O and HDO) in atmospheric waters are widely used as tracers of the hydrological cycle (Jouzel, 2003). In Greenland ice cores, water 13, 30521–30574, 2013 stable isotopes have been used to quantify past changes in climate and in the water 5 cycle. Because this motivates a better understanding of the processes at play from Greenland water present-day studies, we briefly summarize the key findings and questions arising from vapour and these ice core studies. precipitation isotopic A brief description of water isotopes basics is given hereafter. The isotopic compo- composition sition of water is expressed in ‰ unit, using δ notations, defined as a variation of the J.-L. Bonne et al. 10 sample isotopic ratio R compared to a standard isotopic ratio RVSMOW: δ = 1000 × (R/RVSMOW − 1) (1) Title Page 18 18 In this work, we focus on δ O and δD isotopic compositions (corresponding to H2 O and HDO isotopologues) of water vapour and precipitation, based on in situ continuous Abstract Introduction observations. Hereafter, precipitation and vapour observations are respectively noted Conclusions References 15 with the suffixes p and v. Since water stable isotopologues have different saturation vapour pressure and dif- Tables Figures fusivity in the air, fractionation processes occur during phase changes (such as evap- oration or condensation). They produce strong temporal and spatial variations of at- J I mospheric water vapour and precipitation isotopic composition. These variations are J I 20 driven by continuous removal of heavier isotopes during poleward transport, some- times called atmospheric distillation, and are affected by changes in moisture sources Back Close and transport histories. As changes in temperature strongly control this distillation and the isotopic composition of precipitation at mid and high latitudes, this forms the basis Full Screen / Esc for past temperature reconstructions using records of precipitation isotopic composi- Printer-friendly Version 25 tion in archives such as ice cores (Jouzel, 2003). In addition to equilibrium fraction- ation, kinetic processes take place for instance during evaporation or condensation Interactive Discussion on ice crystals. The second order parameter deuterium-excess (hereafter noted d, 30523 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | d = δD − 8 × δ18O) has been introduced to identify deviations from the mean relation- ship between δ18O and δD in meteoric waters (with a mean slope of 8 resulting from ACPD equilibrium fractionation) and highlight kinetic effects (Dansgaard, 1964; Craig and Gor- 13, 30521–30574, 2013 don, 1965; Merlivat and Jouzel, 1979). 5 Greenland ice core records now cover 140 000 yr (Dahl-Jensen et al., 2013). High resolution records have documented the seasonal cycle of surface snow isotopic com- Greenland water position (Johnsen, 1977), and seasonal changes during the past millennia (Vinther vapour and et al., 2010). Initially, the quantitative interpretation of Greenland ice core water stable precipitation isotopic isotope records in terms of temperature was based on an isotope-temperature relation- composition 10 ship following modern spatial surface snow and precipitation data, and surface air or J.-L. Bonne et al. firn temperatures (Dansgaard, 1964; Sjolte et al., 2011). The comparison of past tem- peratures inferred from borehole temperature profiles and from gas fractionation (Sev- eringhaus and Brook, 1999; Dahl-Jensen et al., 1998; Cuffey et al., 1992; Vinther et al., Title Page 2010; Masson-Delmotte et al., 2011) has demonstrated that the isotope-temperature 15 relationship varies through time, possibly due to changes in precipitation seasonality Abstract Introduction (Krinner et al., 1997; Krinner and Werner, 2003) and intermittency (Persson et al., Conclusions References 2011), and in moisture origin. Statistical and backtrajectory analysis have depicted a strong imprint of the North Atlantic Oscillation (NAO), associated with large shifts Tables Figures of the mean moisture sources, in winter and annual ice core isotopic signals, consis- 20 tent with its imprint in instrumental temperature records (Vinther et al., 2010; Casado J I et al., 2012; Sodemann et al., 2008b, a). Rapid strong shifts in d have been docu- mented during abrupt events (Steffensen et al., 2008; Thomas et al., 2009), together J I with significant changes at the orbital scale, possibly related to major changes in mois- Back Close ture sources (Masson-Delmotte et al., 2005; Jouzel et al., 2007). The combination of 25 different ice core records has recently allowed to investigate the regional patterns of Full Screen / Esc past changes in precipitation water stable isotopes and climate (Steen-Larsen et al., 2011; Guillevic et al., 2012). All these studies point out that the quantitative under- Printer-friendly Version standing of Greenland ice core records requires improved comprehension of the differ- ent processes controlling Greenland surface snow isotopic composition. This calls for Interactive Discussion 30524 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | a continuous monitoring of water vapour, precipitation and surface snow isotopic com- position, in order to decipher, at the atmospheric process scale, the drivers of transport, ACPD deposition and post-deposition effects. 13, 30521–30574, 2013 Under the auspices of the GNIP/IAEA (Global Network of Isotopes in Precipita- 5 tion/International Atomic Energy Agency), Greenland coastal precipitation has been sampled at different locations and analysed for water stable isotope composition, at the Greenland water monthly scale, during specific time intervals (Rozanski et al., 1993; Sjolte et al., 2011), vapour and limiting