Acquisition of isotopic composition for surface snow in East Antarctica and the links to climatic parameters

Abstract

International audienceThe isotopic compositions of oxygen and hydrogen in ice cores are invaluable tools for the reconstruction of past climate variations. Used alone, they give insights into the variations of the local temperature, whereas taken together they can provide information on the climatic conditions at the point of origin of the moisture. However, recent analyses of snow from shallow pits indicate that the climatic signal can become erased in very low accumulation regions, due to local processes of snow reworking. The signal-to-noise ratio decreases and the climatic signal can then only be retrieved using stacks of several snow pits. Obviously, the signal is not completely lost at this stage, otherwise it would be impossible to extract valuable climate information from ice cores as has been done, for instance, for the last glaciation. To better understand how the climatic signal is passed from the precipitation to the snow, we present here results from varied snow samples from East Antarctica. First, we look at the relationship between isotopes and temperature from a geographical point of view, using results from three traverses across Antarctica, to see how the relationship is built up through the distillation process. We also take advantage of these measures to see how second-order parameters (d-excess and 17 O-excess) are related to δ 18 O and how they are controlled. d-excess increases in the interior of the continent (i.e., when δ 18 O decreases), due to the distillation process, whereas 17 O-excess decreases in remote areas, due to kinetic fractionation at low temperature. In both cases, these changes are associated with the loss of original information regarding the source. Then, we look at the same relationships in precipitation samples collected over 1 year at Dome C and Vos-tok, as well as in surface snow at Dome C. We note that the slope of the δ 18 O vs. temperature (T) relationship decreases in these samples compared to those from the traverses, and thus caution is advocated when using spatial slopes for past Published by Copernicus Publications on behalf of the European Geosciences Union. 838 A. Touzeau et al.: Acquisition of isotopic composition for surface snow in East Antarctica climate reconstruction. The second-order parameters behave in the same way in the precipitation as in the surface snow from traverses, indicating that similar processes are active and that their interpretation in terms of source climatic parameters is strongly complicated by local temperature effects in East Antarctica. Finally we check if the same relationships between δ 18 O and second-order parameters are also found in the snow from four snow pits. While the d-excess remains opposed to δ 18 O in most snow pits, the 17 O-excess is no longer positively correlated to δ 18 O and even shows anti-correlation to δ 18 O at Vostok. This may be due to a strato-spheric influence at this site and/or to post-deposition processes

Antarctic climate variability on regional and continental scales over the last 2000 years

“…The intermittency of Antarctic precipitation (Masson-Delmotte et al, 2011;Sime et al, 2009), variability in precipitation source regions (Sodemann and Stohl, 2009), and post-depositional effects of snow layers including wind drift and scouring, sublimation, and snow metamorphism (Frezzotti et al, 2007;Ekaykin et al, 2014;Touzeau et al, 2016;Casado et al, 2016;Hoshina et al, 2014;Steen-Larsen et al, 2014) can distort the climate signal preserved within ice cores and produces non-climatic noise. As a result, obtaining a robust climate signal can only be achieved through the combination of multiple ice core records from a given site and/or region, and through the site-specific calibration of the relationships between water stable isotopes and temperature.…”

Numerical experiments on isotopic diffusion in polar snow and firn using a multi-layer energy balance model

“…vapor transport, even in the absence of precipitation or condensation from the atmosphere. This mechanism could explain the 555 parallel evolution of surface snow isotopic composition and temperature described by Steen-Larsen et al (2014) and Touzeau et al (2016) between precipitation events.…”

“…This is particularly timely since many recent studies have studied the parallel evolution of isotopic composition of water vapor and surface snow during summer both in Greenland and Antarctica (Steen-Larsen et al, 2014;Ritter et al, 2016;Casado et al, 2016a;2016b (Touzeau et al, 2016). Indeed, 17 O-excess is strongly influenced by kinetic diffusion driven fractionation which may be quantified by the implementation of 17 O-excess in our Crocus-iso model.…”

“…We chose these two sites because they have been well-studied in the recent years through field campaigns and numerical experiments. In 430 particular, for Dome C, a large amount of meteorological and isotopic data is available (Casado et al, 2016a;Stenni et al, 2016;Touzeau et al, 2016). Typical values of the main climatic parameters for the two studied sites (Summit and Dome C) are given in Table 2, as well as typical δ 18 O range.…”

The influence of the synoptic regime on stable water isotopes in precipitation at Dome C, East Antarctica

“…Recent studies have shown, however, that the in-E. Schlosser et al: Influence of the synoptic regime on stable water isotopes in precipitation at Dome C teraction between the uppermost layers of the snowpack and the overlying atmosphere between precipitation events also plays an important role. This was found in both Greenland Bonne et al, 2014) and Antarctica (Casado et al, 2016a, b;Ritter et al, 2016;Touzeau et al, 2016) as well as in laboratory experiments (Ebner et al, 2017).…”