From atmospheric water isotopes measurement to firn core interpretation in Adélie Land: a case study for isotope-enabled atmospheric models in Antarctica

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 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 1950s 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. We need to progress in our understanding of the influence of the atmospheric hydrological cycle on the water isotopic composition of ice cores. First, we 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, atmospheric water mixing ratio (hereafter humidity) and δ18O) for the different seasons and determine the evolution of key relationships (δ18O versus temperature or humidity) throughout the year: we find that the temperature vs. δ18O relationship is dependent on synoptic events dynamics in winter contrary to summer. Then, this data set is used to evaluate the atmospheric general circulation model ECHAM6-wiso (model version with embedded water stable isotopes) in a coastal region of Adélie Land 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, at different timescales (i.e., seasonal to synoptic). Therefore we demonstrate the added value of long-term water vapor isotopic composition records for model evaluation. Then, as a clear link is found between the isotopic composition of water vapor and precipitation, we assess how isotopic models can help interpret short firn cores. In fact, a virtual firn core built from ECHAM-wiso outputs explains much more of the variability observed in S1C1 isotopic record than a virtual firn core built from temperature only. Yet, deposition and post-deposition effects strongly affect the firn isotopic signal and probably account for most of the remaining misfits between archived firn signal and virtual firn core based on atmospheric modeling.</p

Oxygen and hydrogen isotopic composition of tap waters in France

The isotopic compositions of oxygen (δ18O) and hydrogen (δ2H) are widely used to locate the geo- graphical origin of biological remains or manufactured products. In this paper, we analyse the distributions of δ18O and δ2H in tap waters sampled across France, and in precipitation interpolated with the Online Isotopes in Precipitation Calculator and modelled with the isotope-enabled ECHAM6-wiso model. Our aim is to provide isoscapes usable in archaeology and forensics and evaluate whether the modelled data could be surrogates for measured ones. The δ18O and δ2H in the 396 tap waters sampled varied spatially within a range of 10‰ and 77‰, respectively. Their consistent distributions followed rules summarized by the effects of altitude and dis- tance from the coast. Their variations along the year were small. Therefore, the database provides a solid ref- erence for δ18O and δ2H of the water supply system at the regional scale. The areas with the most uncommon oxygen and hydrogen isotopic compositions (Atlantic coast south of Brittany and the highest elevations in the Alps) are the most accurately traceable areas in provenancing studies. The isotopic compositions of modelled precipitation have the same spatial distributions but different absolute values from those of tap waters. There- fore, our results favour the use of statistical isoscapes rather than general circulation model-based isoscapes in provenancing studies