Background. Under construction
Tools. Under construction
Supervisors. Thomas B. Ryerson
Background. Increasing rates of atmospheric nitrate deposition in mountainous basins, now well documented by
alpine ice cores and emission inventories of the Western countries, involve critical changes in nitrogen (N) availability with consequences on biodiversity (plants, microbes), soils, and
water nutrients (C, N) status leading to vulnerability of critical ecosystem services (i.e., provision of clean freshwater, erosion control, biodiversity). These impacts of higher atmospheric
nitrate deposition remain poorly studied and understood in N-limited mountainous watersheds, and its potential synergetic effect when combined with agricultural land-uses changes is not studied.
In this context, new tools are necessary to better predict mid and long-term consequences of simultaneous changes in agricultural land-uses and atmospheric nitrate deposition.
Tools. Using a high-resolution multi-isotopic technique combining 17O, 18O and 15N signatures of atmospheric nitrate in aerosols, precipitations, soils, vegetation and stream waters, we tracked and quantified the temporal and spatial evolution of atmospheric nitrate deposition partitioning in the N budget of a subalpine watershed in the French Alps. The evolution of atmospheric nitrate isotopic signatures provides key information on the main biotic and abiotic processes involved in N dynamics under pristine and anthropogenic influences. This multi-isotopic technique, combined with chemical analysis, enlightened our understanding of N cycle at the watershed scale, and provided good indices of the "N saturation" status of the ecosystem at the Lautaret Pass, by discriminating allochthonous atmospheric nitrate and nitrate from terrestrial sources.
Background. Fast temperature changes cause isotopic fractionation of several gaseous species in Antarctic firn because of thermal diffusion, thus creating specific isotopic signatures trapped in air bubbles when snow becomes ice. This process is called "close-off fractionation", and the study of this phenomenon coupled with models on heat penetration and gaseous diffusion in Antarctic firn enables a better understanding of specific paleoclimatic events magnitude. Neon isotopes are good indicators of such events as 22Ne/21Ne ratio has remained constant on Earth for over one million years. Determining Neon isotopes thermal diffusion coefficient expression is the first step towards the implementation of close-off fractionation in models.
Tools. We created a laboratory experiment to provoke Neon isotopic fractionation along a temperature gradient of about 15°C. Briefly, a metallic cell with multiple valves was filled with neon gaz, then immersed in a bath divided in two section, each with a different temperature. After equilibration, the valves of the cell were closed, thus separating Neon isotopes accordingly with temperature. Such induced isotopic fractionation was then measured on a dual inlet mass spectrometer.
Supervisor. Jeff Severinghaus
Background. Antarctica is the coldest, driest, windiest and most isolated continent in the world, which makes it a unique location for several
Social, Medical or Earth and Universe sciences. Concordia Station, located in the heart of the continent on Dome C, was built in 2005 and is a French-Italian research station with interest in
astrophysics, glaciology, seismology, atmospheric physics and chemistry, medical research and human behaviour. Every year, a crew of around 13 people spend a whole year in the station, taking
care of the experimental setups, guaranteeing the routine sampling and dedicating their time to science.
Tools. As a glaciologist winterovering personnel, I was in charge of several glaciology and atmospheric chemistry research projects for LGGE (more details in the Field Work section).
Supervisor. Bruno Jourdain
Background. Biogenic emissions of COV by plants have multiple potential impacts on terrestrial ecosystems: not only on organisms functioning at the individual scale via their role as defense and communication compounds, but also on biodiversity of vegetal communities via their influence on air quality and climate. The understanding of plants VOC emissions response to stress factors such as temperature and light increase is important in order to better constrain our knowledge of air pollution/climate/biogeochemical cycles interactions.
Tools. An experimental setup to measure Aleppo Pine and Rosemary VOC emissions along light and temperature gradient was used in a specific greenhouse dedicated to scientific research. VOC emissions were trapped on adsorbent cartridges, thermally desorbed and analysed on a GC-MS. H20 and CO2 were also monitored to infer photosynthesis rates.
Supervisor. Michael Staudt