Using triple water isotopes signatures of surface snow to gauge metamorphism in Antarctica

Abstract

<p>Water isotopic composition is a key proxy for past climate reconstructions using deep ice cores from Antarctica. As precipitation forms, the local temperature is imprinted in the snowfalls δ<sup>18</sup>O. However, this climatic signal can be erased after snow deposition when snow is exposed to the atmosphere for a long time in regions with extremely low accumulation. Understanding this effect is crucial for the interpretation of ice core records from the extremely dry East Antarctic Plateau, where post-deposition processes such as blowing snow or metamorphism affect the physical and chemical properties of snow during the long periods of snow exposure to the atmosphere. Despite the importance of these processes for the reliable reconstruction of temperature from water isotopic composition in ice cores, the tools required to quantify their impacts are still missing. Here, we present a first year-long comparison between (a) time series of surface snow isotopic composition including d-excess and <sup>17</sup>O-excess at Dome C and (b) satellite observations providing information on snow grain size, a marker of surface metamorphism. Long summer periods without precipitation tend to produce a surface snow metamorphism signature erasing the climatic signal in the surface snow δ<sup>18</sup>O. Using a simple model, we demonstrate that d-excess and <sup>17</sup>O-excess allow the identification of the latent fluxes induced by metamorphism, and their impact on surface snow isotopic composition. In turn, their measurements can help improve climate reconstructions based on δ<sup>18</sup>O records ice by removing the influence of snow metamorphism.</p>