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

Abstract

Abstract. The correct derivation of paleotemperatures from ice cores requires exact knowledge of all processes involved before and after the deposition of snow and the subsequent formation of ice. At the Antarctic deep ice core drilling site Dome C, a unique data set of daily precipitation amount, type, and stable water isotope ratios is available that enables us to study in detail atmospheric processes that influence the stable water isotope ratio of precipitation. Meteorological data from both automatic weather station and a mesoscale atmospheric model were used to investigate how different atmospheric flow patterns determine the precipitation parameters. A classification of synoptic situations that cause precipitation at Dome C was established and, together with back-trajectory calculations, was utilized to estimate moisture source areas. With the resulting source area conditions (wind speed, sea surface temperature, and relative humidity) as input, the precipitation stable isotopic composition was modeled using the so-called Mixed Cloud Isotope Model (MCIM). The model generally underestimates the depletion of 18 O in precipitation, which was not improved by using condensation temperature rather than inversion temperature. Contrary to the assumption widely used in ice core studies, a more northern moisture source does not necessarily mean stronger isotopic fractionation. This is due to the fact that snowfall events at Dome C are often associated with warm air advection due to amplification of planetary waves, which considerably increases the site temperature and thus reduces the temperature difference between source area and deposition site. In addition, no correlation was found between relative humidity at the moisture source and the deuterium excess in precipitation. The significant difference in the isotopic signal of hoarfrost and diamond dust was shown to disappear after removal of seasonality. This study confirms the results of an earlier study carried out at Dome Fuji with a shorter data set using the same methods.

Challenges associated with the climatic interpretation of water stable isotope records from a highly resolved firn core from Adélie Land, coastal Antarctica

“…Fernandoy et al, 2018;Bertler et al, 2018;Schlosser et al, 2004;Dittmann et al, 2016). While distillation processes are expected theoretically to relate condensation temperature with precipitation isotopic composition, a number of deposition processes can distort this relationship: changes in moisture sources (Stenni et al, 2016), intermittency or seasonality of precipitation (Sime et al, 2008), boundary layer processes affecting the links between condensation and surface air temperature (Krinner et al, 2008), and several post-deposition processes, such as the effects of winds (Eisen et al, 2008), snow-air exchanges (Casado et al, 2016;Ritter et al, 2016), and diffusion processes in snow and ice (e.g. Johnsen, 1977).…”

“…Delmotte et al, 2000). These features have been explored through the identification of back-trajectory clusters and their relationship with δ 18 Od-excess relationships, including phase lags (Markle et al, 2012;Caiazzo et al, 2016;Schlosser et al, 2017).…”

Water stable isotope spatio-temporal variability in Antarctica in 1960–2013: observations and simulations from the ECHAM5-wiso atmospheric general circulation model

“…The ocean surface boundary conditions (sea ice included) are also prescribed based on ERA-40 and ERA-Interim data. Isotope values of ocean surface isotopic composition are based on a compilation of observational data (Schmidt et al, 2007). The simulation was performed at a T106 resolution (which corresponds to a mean horizontal grid resolution of approx.…”

“…One study used climate projections in response to increased atmospheric CO 2 concentration to explore isotope-temperature relationships in a world warmer than today and suggested a changing temporal isotope-temperature relationship due to changing covariance between temperature and precipitation (Sime et al, 2009). Several observational and modelling studies have also evidenced different isotope-temperature relationships between the spatial relationship and those calculated at the seasonal (Morgan and van Ommen, 1997) or inter-annual scale (Schmidt et al, 2007).…”

Evaluation of Seasonal and Synoptic Changes in Snow Accumulation in Antarctica between Five Reanalyses Products and In Situ Observations

“…The impact of the wind in both methods cannot be removed entirely [17,46]. Other ablation processes show little effect on the evaluation of high snow accumulation events at synoptic timescales in Antarctica [13,38,39]. Previous studies have suggested that high accumulation events identified by a certain threshold are induced by precipitation at a synoptic timescale, and in situ measurements could be used to assess the performance of precipitation in reanalyses [8,13,39].…”