Three-year monitoring of stable isotopes of precipitation at Concordia Station, East Antarctica

Abstract

Abstract. Past temperature reconstructions from Antarctic ice cores require a good quantification and understanding of the relationship between snow isotopic composition and 2 m air or inversion (condensation) temperature. Here, we focus on the French–Italian Concordia Station, central East Antarctic plateau, where the European Project for Ice Coring in Antarctica (EPICA) Dome C ice cores were drilled. We provide a multi-year record of daily precipitation types identified from crystal morphologies, daily precipitation amounts and isotopic composition. Our sampling period (2008–2010) encompasses a warmer year (2009, +1.2 °C with respect to 2 m air temperature long-term average 1996–2010), with larger total precipitation and snowfall amounts (14 and 76 % above sampling period average, respectively), and a colder and drier year (2010, −1.8 °C, 4 % below long-term and sampling period averages, respectively) with larger diamond dust amounts (49 % above sampling period average). Relationships between local meteorological data and precipitation isotopic composition are investigated at daily, monthly and inter-annual scale, and for the different types of precipitation. Water stable isotopes are more closely related to 2 m air temperature than to inversion temperature at all timescales (e.g. R2 = 0.63 and 0.44, respectively for daily values). The slope of the temporal relationship between daily δ18O and 2 m air temperature is approximately 2 times smaller (0.49 ‰ °C−1) than the average Antarctic spatial (0.8 ‰ °C−1) relationship initially used for the interpretation of EPICA Dome C records. In accordance with results from precipitation monitoring at Vostok and Dome F, deuterium excess is anti-correlated with δ18O at daily and monthly scales, reaching maximum values in winter. Hoar frost precipitation samples have a specific fingerprint with more depleted δ18O (about 5 ‰ below average) and higher deuterium excess (about 8 ‰ above average) values than other precipitation types. These datasets provide a basis for comparison with shallow ice core records, to investigate post-deposition effects. A preliminary comparison between observations and precipitation from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis and the simulated water stable isotopes from the Laboratoire de Météorologie Dynamique Zoom atmospheric general circulation model (LMDZiso) shows that models do correctly capture the amount of precipitation as well as more than 50 % of the variance of the observed δ18O, driven by large-scale weather patterns. Despite a warm bias and an underestimation of the variance in water stable isotopes, LMDZiso correctly captures these relationships between δ18O, 2 m air temperature and deuterium excess. Our dataset is therefore available for further in-depth model evaluation at the synoptic scale.

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

“…2, hoarfrost mainly occurs in winter, at deep temperatures when absolute humidity is comparatively low. While 130 days with hoarfrost have temperatures between −60 and −70 • C, about 70 hoarfrost days are in the temperature range −60 to −50 • C; only less than 30 days show temperatures higher than −50 • C. This means that hoarfrost does not have a specific fingerprint due to its crystal type and formation process, as stated in a preliminary study by Stenni et al (2016), but, as speculated about qualitatively by Stenni et al (2016) already, the different signal is due to the low temperatures prevailing at days with hoarfrost formation.…”

“…Hoarfrost exhibited significantly lower δ 18 O and δD values and higher deuterium excess than snowfall and diamond dust. Whereas Stenni et al (2016) state that hoarfrost has a distinct fingerprint among the various precipitation types, implying that moisture sources and or the hydrological cycle might be different for hoarfrost, our current, more detailed study has shown that this "fingerprint" is due to the fact that hoarfrost occurs predominantly during the cold period. Relatively large amounts of hoarfrost are measured after synoptic snowfall events, when humidity is still increased after moisture transport from lower latitudes, implying that hoarfrost basically has the same moisture sources as the other precipitation types.…”

“…However, at present, no explanation for this can be offered. The assumption generally used in ice core studies (e.g., Stenni et al, 2016) that the temperature at the top of the inversion layer represents the condensation temperature could not be proven.…”

“…8b) shows no significant differences between the precipitation types. Slopes for the different crystal types are discussed in detail and compared to other Antarctic sites in Stenni et al (2016) (modeled/observed values, daily/monthly values, inversion/2 m temperature). At the time of our study, the time series of analyzed samples was not long enough to calculate statistically significant slopes for the different synoptic situations.…”

“…The precipitation amount and stable isotope data are available as a Supplement to Stenni et al (2016) at https://www.the-cryosphere.net/10/2415/2016/. AWS data are from US AWS Dome C II (http://amrc.ssec.wisc.edu).…”