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  • Final Report Summary - COMBINISO (Quantitative picture of interactions between climate, hydrological cycle and stratospheric inputs in Antarctica over the last 100 years via the combined use of all water isotopes)

COMBINISO Report Summary

Project ID: 306045
Funded under: FP7-IDEAS-ERC
Country: France

Final Report Summary - COMBINISO (Quantitative picture of interactions between climate, hydrological cycle and stratospheric inputs in Antarctica over the last 100 years via the combined use of all water isotopes)

COMBINISO addressed the question of recent climate change in Antarctica and associated modification in the atmospheric water cycle. This question is central since (1) climate change is not well documented in Antarctica because of the lack of direct instrumental records and (2) it represents the largest freshwater reservoir of the world. The evolution of atmospheric water cycle has thus strong impact on the surface mass balance. In the absence of direct instrumental records, reconstructions of climate change and atmospheric water cycle organization in Antarctica rely on water isotope measurements in snow or ice core.
Within COMBINISO, we have first worked on the process of acquisition of the climate and water cycle signals in water isotopes records in snow and ice core. The idea was to combine all water isotopes in the continuum between atmospheric water vapor, precipitation, surface snow and subsurface snow at low temperature (East Antarctic plateau) with an approach combining laboratory experiments, field measurements and modeling approaches. Because low temperature is associated with very low humidity, we have developed a new laser absorption spectrometer able to measure with high precision stable water isotopes in water vapor at very low humidity. We also realized experiments in cloud chamber at low temperature to propose a new formulation of isotopic fractionation at snow condensation. Then, we organized 3 field studies over 3 consecutive years in East Antarctica for continuous measurements of water isotopes in the water vapor, precipitation, surface and subsurface snow. These experiments permit to quantify the link between temperature and snow isotopic content under different atmospheric influences (precipitation or clear sky). On the modeling side, we provided the first snow model including a physical description of the snow microstructure and water isotopes diffusion, a key tool to interpret climate variations from water isotopes records in snow and ice.
This project also evidence the contribution of stratospheric moisture origin on the accumulation in remote region of East Antarctica especially during snow events occurring during cold winter days. This result was obtained using combination of 10Be, tritium and 17O-excess data in several snow pits as well as modeling experiments. We thus provided the first general circulation model equipped with description of tritium to link the tritium concentration at the Antarctic surface to stratospheric moisture input.
Finally, the reconstruction of climate and moisture origin over the last 100 years relied on heavy analytical program for measurements of all water isotopes on a bunch of snow cores in East Antarctica (coastal and inland regions). Post-deposition effects were corrected by analyses of several snow cores at the same sites as well as use of snow model equipped with isotopes and quantification of isotopic fractionation at sublimation obtained from field experiments.
Several perspectives are opened by this project such as a (1) new technological avenue for a new generation of laser absorption spectrometer, (2) installation of observatories of water vapor isotopic composition in very dry and cold regions of Antarctica and (3) new modeling tools at the small scale (first snow model equipped with isotopes) and global scale (first atmospheric general circulation model equipped with tritium) with application beyond the field of climate change.

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