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 NO_x = 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 NO_x 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 NO_x 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.

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.

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.

Les milieux polaires et subpolaires ne sont pas dépourvus de parasites. Chez les manchots royaux, les ectoparasites tels que les tiques (Ixodes uriae) sont suspectés d’avoir des effets marqués sur la santé et le succès reproducteur des adultes. En utilisant un traitement expérimental réduisant drastiquement l’abondance d’ectoparasites chez des adultes reproducteurs, nous avons pu démontrer que l’infestation par les ectoparasites induit une augmentation du stress physiologique caractérisé par des taux élevés de corticostérone (glucocorticoïde) et une situation de stress oxydant. Bien que l’éradication des ectoparasites n’ait pas d’influence notable sur le succès d’éclosion des œufs ou la survie des poussins durant l’élevage, le traitement améliore visiblement la croissance des poussins jusqu’à l’émancipation, avec des effets positifs probables sur leur survie future. Il semble donc que les ectoparasites exercent une pression de sélection naturelle non-négligeable chez le manchot royal.

Les endothermes polaires et subpolaires, adaptés à un climat froid, pourraient se révéler particulièrement sensibles au stress thermique dans un contexte de réchauffement global. L'hypothèse température-agression – qui propose un lien causal entre températures ambiantes élevées et motivation agressive – pourrait accentuer le stress thermique. Essentiellement étudiée pour des raisons socio-économiques, l’hypothèse est peu investiguée chez les espèces sauvages. L’étude de manchots royaux en période de reproduction (n= 85, Crozet), a permis de mettre en évidence des relations positives entre paramètres climatiques (température, radiation solaire), température sous-cutanée, indicateurs comportementaux de stress thermique (halètement, écartement des ailerons) et agressivité envers les congénères. Nos résultats ouvrent de nouvelles perspectives écologiques pour l'hypothèse température-agression, et encouragent l'étude du stress thermique dans les écosystèmes polaires.