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Casado, M., Leroy-Dos Santos, C., Fourré, E., Favier, V., Agosta, C., Arnaud, L., Prié, F., Akers, P. D., Janssen, L., Kittel, C., Savarino, J., and Landais, A.. (2022). Water vapor isotopic signature along the EAIIST traverse.
Abstract: Stable Water Isotopes Are A Tracer Of Hydrological Processes And A Paleoclimate Proxy From Ice Core Records. The Interpretation Of The Latter Relies On Fractionation Processes Throughout The Hydrological Cycle, From The Evaporation Over The Ocean, During Each Precipitation Event, And During Post-deposition Processes, In Particular Due To The Exchanges Between The Snow And The Moisture In The Atmosphere. Thanks To New Developments In Infrared Spectroscopy, It Is Now Possible To Monitor Not Only The Snow Isotopic Composition But Also The Vapour Continuously, And Thus Document Exchanges Between The Snow And The Vapour. On The East Antarctic Plateau, Records Of Water Vapour Isotopic Composition In Kohnen And Dome C During Summer Have Revealed Significant Diurnal Variability Which Can Be Used To Address The Exchange Between Surface Snow And Atmospheric Water Vapour As Well As The Stability Of The Atmospheric Boundary Layer. in This Study, We Present The First Vapour Monitoring On A Transect Across East Antarctica For A Period Of 3 Months From November 2019 To February 2020 During The Eaiist Traverse, Covering More Than 3600 Km. In Parallel, We Also Monitored The Vapour Isotopic Composition At Two Stations: Dumont D’urville (Ddu), The Starting Point, And Dome C, Half Way Through. Efforts On The Calibration On Each Monitoring Station, As Well As Cross-calibration Of The Different Instruments Offer A Unique Opportunity To Compare Both The Spatial And Temporal (Diurnal Variability Or At The Scale Of Several Days) Gradients Of Humidity, Temperature And Water Vapour Isotopic Composition In East Antarctica During The Summer Season. with The Use Of The Modele Atmospherique Régional (Mar), We Compare The Variability Measured In Water Vapour Isotopic Composition, Temperature And Humidity With The Different Systems (Fixed Or Mobile Location). Although Further Comparisons With The Surface Snow Isotopic Composition Are Required To Quantify The Impact Of The Snow-atmosphere Exchanges On The Local Surface Mass Balance, These Three Simultaneous Measurements Of The Vapour Isotopic Composition Show The Potential Of Using Water Stables Isotopes To Evaluate Hydrological Processes In East Antarctica.
Programme: 1205
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Dedieu, J.-P., A. Wendleder, B. Cerino, J. Boike, E. Bernard, J.-C. Gallet, and H.-W. Jacobi. (2021). Snow change detection from polarimetric SAR time-series at X-band (Svalbard, Norway), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-149..
Abstract:
Due to recent climate change conditions, i.e. increasing temperatures and changing precipitation patterns, arctic snow cover dynamics exhibit strong changes in terms of extent and duration. Arctic amplification processes and impacts are well documented expected to strengthen in coming decades. In this context, innovative observation methods are helpful for a better comprehension of the spatial variability of snow properties relevant for climate research and hydrological applications. Microwave remote sensing provides exceptional spatial and temporal performance in terms of all-weather application and target penetration. Time-series of Synthetic Active Radar images (SAR) are becoming more accessible at different frequencies and polarimetry has demonstrated a significant advantage for detecting changes in different media. Concerning arctic snow monitoring, SAR sensors can offer continuous time-series during the polar night and with cloud cover, providing a consequent advantage in regard of optical sensors. The aim of this study is dedicated to the spatial/temporal variability of snow in the Ny-Ålesund area on the Br∅gger peninsula, Svalbard (N 78°55’ / E 11° 55’). The TerraSAR-X satellite (DLR, Germany) operated at X-band (3.1 cm, 9.6 GHz) with dual co-pol mode (HH/VV) at 5-m spatial resolution, and with high incidence angles (36° to 39°) poviding a better snow penetration and reducing topographic constraints. A dataset of 92 images (ascending and descending) is available since 2017, together with a high resolution DEM (NPI 5-m) and consistent in-situ measurements of meteorological data and snow profiles including glaciers sites. Polarimetric processing is based on the Kennaugh matrix decomposition, copolar phase coherence (CCOH) and copolar phase difference (CPD). The Kennaugh matrix elements K0, K3, K4, and K7 are, respectively, the total intensity, phase ratio, intensity ratio, and shift between HH and VV phase center. Their interpretation allows analysing the structure of the snowpack linked to the near real time of in-situ measurements (snow profiles). The X-band signal is strongly influenced by the snow stratigraphy: internal ice layers reduce or block the penetration of the signal into the snow pack. The best R2 correlation performances between estimated and measured snow heights are ranging from 0.50 to 0.70 for dry snow conditions. Therefore, the use of the X-band for regular snow height estimations remains limited under these conditions. Conversely, this study shows the benefit of TerraSAR-X thanks to the Kennaugh matrix elements analysis. A focus is set on the Copolar Phase Difference (CPD, Leinss 2016) between VV and HH polarization: Φ CPD = Φ VV – Φ HH. Our results indicate that the CPD values are related to the snow metamorphism: positive values correspond to dry snow (horizontal structures), negative values indicate recrystallization processes (vertical structures). Backscattering evolution in time offer a good proxy for meteorological events detection, impacting on snow metamorphism. Fresh snowfalls or melting processes can then be retrieved at the regional scale and linked to air temperature or precipitation measurements at local scale. Polarimetric SAR time series is therefore of interest to complement satellite-based precipitation measurements in the Arctic. Programme: 1126
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Julien Jumelet, Florent Tencé, Alain Sarkissian, Slimane Bekki, Philippe Keckhut. (2021). 10 years of Polar Stratospheric Clouds lidar measurements at the French antarctic station Dumont d'Urville.
Abstract: Polar Stratospheric Clouds (PSCs) play a primary role in polar stratospheric ozone depletion processes. Aside from recent improvements in both spaceborne monitoring as well as investigations on microphysics and modeling, there are still caveats on building a comprehensive picture of the PSC particle population, especially considering the fine optical signatures of some particles. In that regard, groundbased instruments provide fine and long term reference measurements that complement the global spaceborne coverage. Operated at the French antarctic station Dumont d’Urville (DDU) in the frame of the international Network for the Detection of Atmospheric Composition Change (NDACC), the Rayleigh/Mie/Raman lidar provides over the years a solid dataset to feed both process and classification studies, by monitoring cloud and aerosol occurrences in the upper troposphere and lower stratosphere. Located on antarctic shore (66°S – 140°E), the station has a privileged access to polar vortex dynamics. Measurements are weather-dependent with a yearly average of 130 nights of monitoring. Expected PSC formation temperatures are used to evaluate the whole PSC season occurrence statistics. We hereby present a consolidated dataset from 10 years of lidar measurements using the 532nm backscatter ratio, the aerosol depolarisation and local atmospheric conditions to help in building an aerosol/cloud classification. Overall, the DDU PSC pattern is very consistent with expected typical temperature controlled thresholds. Supercooled Ternary Solution (STS) particles are the most observed particle type, closely followed by Nitric Acid Trihydrate (NAT). ICE clouds are more rarely observed. The measurements also feature significant and detailed signatures of various aerosols events having reached the polar antarctic stratosphere, like the Calbuco eruption (2015) or the 2 australian wildfires episodes (2009 and 2019). We aim at refining the identification of those aerosols to include their impact in the scope of the scientific questions studied at DDU.
Programme: 209
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Vincent Lesur, Aude Chambodut. (2020). The French network of magnetic observatories.
Programme: 139
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Sarah Albertin, Joël Savarino, Slimane Bekki, Albane Barbero, Roberto Grilli, Quentin Fournier, Irène Ventrillard, Nicolas Caillon, Kathy Law. (2023). Diurnal variations in oxygen and nitrogen isotopes of atmospheric nitrogen dioxide and nitrate: implications for tracing NOx oxidation pathways and emission sources.
Abstract:
Abstract. The oxygen (????17O) and nitrogen (????15N) isotopic compositions of atmospheric nitrate (NO3-) are widely used as tracers of its formation pathways, precursor (nitrogen oxides NOx = nitric oxide NO + nitrogen NO2) emission sources, and physico-chemical processing. However, the critical lack of observations on the multi-isotopic composition of NO2 maintains significant uncertainties regarding the links between the isotopic composition of NOx and NO3-, which may bias estimates of the NO3- formation processes and the distribution of sources. We report here on the first simultaneous atmospheric observations of ????17O and ????15N in NO2 and NO3-. The measurements were carried out at sub-daily (ca. 3 h) resolution over two non-consecutive days in an Alpine city in February 2021. Important diurnal variabilities are observed in both NO2 and NO3- multi-isotopic composition. ????17O of NO2 and NO3- range from 19.6 to 40.8 ‰ and 18.7 to 26 ‰, respectively. During both daytime and nighttime, the variability of ????17O(NO2) is mainly driven by the oxidation of NO by ozone, with a substantial contribution from peroxy radicals in the morning. NO3- local mass balance equations, constrained by observed ????17O(NO2), suggest that during the first day of sampling NO3- was formed locally from the oxidation of NO2 by hydroxyl radicals during the day, and via heterogeneous hydrolysis of dinitrogen pentoxide during the night. For the second day, calculated and observed ????17O(NO3-) do not match, particularly daytime values. The effects on ????17O(NO3-) of a Saharan dust event that occurred during the second day and winter boundary layer dynamics are discussed. ????15N of NO2 and NO3- ranged from -10.0 to 19.7 ‰ and -4.2 to 14.8 ‰, respectively. Consistent with theoretical predictions of N isotope fractionation, the important variability of ????15N(NO2) is explained by significant post-emission equilibrium N fractionation. After accounting for this effect, vehicle exhaust is found to be the primary source of NOx emissions at the sampling site. ????15N(NO3-) is closely linked to ????15N(NO2) variability, which bring further evidence of fast and local processing, but uncertainties on current N fractionation factors during NO2 to NO3- conversion are underscored. Overall, this detailed investigation highlights the potential and the necessity to use ????17O and ????15N in NO2 and NO3- to trace quantitatively the sources and formation chemistry of NO3-, particularly in urban environments in winter. Programme: 1215
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Floriane Provost, Dimitri Zigone, Emmanuel Le Meur, Jean-Philippe Malet, Clément Hibert. (2023). Surface dynamics and history of the calving cycle of the Astrolabe glacier (Antarctica) derived from optical imagery.
Abstract:
Abstract. The recent calving of the Astrolabe glacier (Terre Adélie, East Antarctica) in November 2021 presents an opportunity to better understand the processes leading to ice fracturing. Optical satellite imagery is used to retrieve the calving cycle of the glacier since 2000 by mapping the ice front location. A recent archive of high resolution optical images from Sentinel-2 is used to measure the ice motion and the ice strain rates for the period 2017–2021 in order to document fractures and rift evolution. These observations are compared with sea ice extent and concentration measurements. We found that a significant change in the sea ice melting periodicity at the vicinity of the Astrolabe glacier occurred in the last decade (2011–2021) with respect to previous observations (1979–2011). After 2011, the occurrence of consecutive years of high sea-ice concentration at the vicinity of the glacier seems to have favored the ice tongue spatial extension. This lead to an unprecedentedly observed extension of the ice tongue until November 2021. The analysis of strain rate time series revealed that the glacier dislocated suddenly in June 2021 in the middle of the winter before releasing an iceberg of around 20 km2 in November 2021 at the onset of sea ice melting season. These observations suggest that although the presence of sea ice favors glacier extension, its buttressing effect may not be sufficient to prevent fracture opening. Programme: 411
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Christophe Leroy-Dos Santos, Elise Fourré, Cécile Agosta, Mathieu Casado, Alexandre Cauquoin, Martin Werner, Benedicte Minster, Frederic Prié, Olivier Jossoud, Leila Petit, Amaëlle Landais. (2023). From atmospheric water isotopes measurement to firn core interpretation in Adelie Land: A case study for isotope-enabled atmospheric models in Antarctica.
Abstract:
Abstract. In a context of global warming and sea level rise acceleration, it is key to estimate the evolution of the atmospheric hydrological cycle and temperature in the polar regions, which directly influence the surface mass balance of the Arctic and Antarctic ice sheets. Direct observations are available from satellite data for the last 40 years and a few weather data since the 50’s in Antarctica. One of the best ways to access longer records is to use climate proxies in firn or ice cores. The water isotopic composition in these cores is widely used to reconstruct past temperature variations. In order to progress in our understanding of the influence of the atmospheric hydrological cycle on the water isotopic composition, we first present a 2-year long time series of vapor and precipitation isotopic composition measurement at Dumont d’Urville station, in Adélie Land. We characterize diurnal variations of meteorological parameters (temperature, humidity and δ18O) for the different seasons and to determine the evolution of key relationships (δ18O versus temperature or humidity) along the year: we found mean annual slopes of 0.5 and 0.4 ‰ °C−1 for the relationship of δ18O vs. temperature in the water vapor and in the precipitation respectively. Then, this data set is used to evaluate the Atmospheric General Circulation Model ECHAM6-wiso (model version with embedded water stable isotopes) in a region where local conditions are controlled by strong katabatic winds which directly impact the isotopic signal. We show that a combination of continental (79 %) and oceanic (21 %) grid cells leads model outputs (temperature, humidity and δ18O) to nicely fit the observations, even winter extreme synoptic events are represented in the model. Therefore we demonstrate the added value of long-term water vapor isotopic composition records. Then, as a clear link is found between water vapor and precipitation isotopic composition, we evaluate how isotopic enabled models can help interpreting short firn cores. Programme: 1110
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Antoine Grisart, Mathieu Casado, Vasileios Gkinis, Bo Vinther, Philippe Naveau, Mathieu Vrac, Thomas Laepple, Bénédicte Minster, Fréderic Prié, Barbara Stenni, Elise Fourré, Hans-Christian Steen Larsen, Jean Jouzel, Martin Werner, Katy Pol, Valérie Masson-Delmotte, Maria Hoerhold, Trevor Popp, Amaelle Landais. (2022). Sub-millennial climate variability from high resolution water isotopes in the EDC ice core.
Abstract:
Abstract. The EPICA Dome C (EDC) ice core provides the longest continuous climatic record covering the last 800 000 years (800 kyrs). Obtaining homogeneous high resolution measurements and accounting for diffusion provide a unique opportunity to study the evolution of decadal to millennial variability within the past glacial and interglacial periods. We present here a compilation of high resolution (11 cm) water isotopic records with 27 000 δ18O measurements and 7 920 δD measurements (covering respectively 94 % and 27 % of the whole EDC record), including published and new measurements (2 900 for both δ18O and δD) over the last 800 kyrs on the EDC ice core. We show that overlapping measurement series performed over multiple depth ranges over the past 20 years, using different analytical methods and in different laboratories, are consistent within analytical uncertainty, and therefore can be combined to provide a homogeneous data set. A frequency decomposition of the most complete δ18O record and a simple assessment of the possible influence of diffusion on the measured profile shows that the variability during glacial periods at multi-decadal to multi-centennial timescale is higher than variability of the interglacial periods. This analysis shows as well that during interglacial periods characterized by a temperature optimum at its beginning, the multi-centennial variability is the strongest over this temperature optimum. Programme: 1110
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Bazin L, Landais A, Masson-Delmotte V, Ritz C, Picard G, Capron E, Jouzel J, Dumont M, Leuenberger M, Prié F, . (2015). Phase relationships between orbital forcing and the composition of air trapped in Antarctic ice cores
. Climate of the Past Discussions, 11(2), 1437–1477.
Abstract: Orbital tuning is central for ice core chronologies beyond annual layer counting, available back to 60 ka (i.e. thousand of years before 1950) for Greenland ice cores.
While several complementary orbital tuning tools have recently been developed using delta 18O atm,delta O2/N2, and air content with different orbital targets, quantifying their uncertainties remains a challenge. Indeed, the exact processes linking variations of these parameters, measured in the air trapped in ice, to their orbital targets are not yet fully nderstood. Here, we provide new series of delta O2/N2 and delta 18O atm data encompassing Marine Isotopic Stage (MIS) 5 (between 100–160 ka) and the oldest part(380–800 ka) of the East Antarctic EPICA Dome C (EDC) ice core. For the first time, the measurements over MIS 5 allow an inter-comparison of delta O2/N2 and delta 18O atm records from three East Antarctic ice core sites (EDC, Vostok and Dome F). This comparison highlights a site-specific relationship between delta O2/N2 and its local summer solstice insolation. Such a relationship increases the uncertainty associated with the use of delta O2/N2 as a tool for orbital tuning. Combining records of delta 18O atm and delta O2/N2 from Vostok and EDC, we evidence a loss of orbital signature for these two parameters during periods of minimum eccentricity (~400,~720–800 ka). Our dataset reveals a time-varying lag between delta O2/N2 and delta 18O atm over the last 800 ka that we interpret as variations of the lag between delta 18O atm and precession. Large lags of ~5 ka are identified during Terminations I and II, associated with strong Heinrich events. On the opposite, minimal lags (~1–2 ka) are identified during four periods characterized by high eccentricity, intermediate ice volume and no Heinrich events (MIS 6–7, the end of MIS 9, MIS 15 and MIS 17). We therefore suggest that the occurrence of Heinrich events influences the response of delta 18O atm to precession. Programme: 902
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Fischer H, Severinghaus J, Brook E, Wolff E, Albert M, Alemany O, Arthern R, Bentley C, Blankenship D, Chappellaz J, Creyts T, Dahl-Jensen D, Dinn M, Frezzotti M, Fujita S, Gallee H, Hindmarsh R, Hudspeth D, Jugie G, Kawamura K, Lipenkov V, Miller H, Mulvaney R, Parrenin F, Pattyn F, Ritz C, Schwander J, Steinhage D, van Ommen T, Wilhelms F, . (2013). Where to find 1.5 million yr old ice for the IPICS “Oldest-Ice” ice core
. 1814-9324, 9(6), 2489–2505.
Abstract: The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful pre-site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e., more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice.
Programme: 902
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