Precipitation regime and stable isotopes at Dome Fuji, East Antarctica

Abstract

Abstract. A unique set of 1-year precipitation and stable water isotope measurements from the Japanese Antarctic station, Dome Fuji, has been used to study the impact of the synoptic situation and the precipitation origin on the isotopic composition of precipitation on the Antarctic Plateau. The Antarctic Mesoscale Prediction System (AMPS) archive data are used to analyse the synoptic situations that cause precipitation. These situations are investigated and divided into five categories. The most common weather situation during a precipitation event is an upper-level ridge that extends onto the Antarctic Plateau and causes strong northerly advection from the ocean. Most precipitation events are associated with an increase in temperature and wind speed, and a local maximum of δ 18 O. During the measurement period, 21 synoptically caused precipitation events caused 60 % of the total annual precipitation, whereas the remaining 40 % were predominantly attributed to diamond dust. By combining the synoptic analyses with 5-day back-trajectories, the moisture source regions for precipitation events were estimated. An average source region around a latitude of 55 • S was found. The atmospheric conditions in the source region were used as initial conditions for running a Rayleigh-type isotopic model in order to reproduce the measured isotopic composition of fresh snow and to investigate the influence of the precipitation source region on the isotope ratios. The model represents the measured annual cycle of δ 18 O and the second-order isotopic parameter deuterium excess reasonably well, but yields on average too little fractionation along the transport/cooling path. While simulations with an isotopic general circulation model (GCM) (ECHAM5-wiso) for Dome Fuji are on average closer to the observations, this model cannot reproduce the annual cycle of deuterium excess. In the event-based analysis, no evidence of a correlation of the measured deuterium excess with the latitude of the moisture source region or the corresponding conditions was identified. Contrary to the assumption used for decades in ice core studies, a more northerly moisture source does not necessarily mean a larger temperature difference between source area and deposition site, thus a more depleted precipitation in heavy isotopes with a higher deuterium excess.

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

“…This, for the first time, allows us to study in detail the synoptic conditions that lead to precipitation at Dome C and how they are related to the precipitation stable isotope ratios. We compare our results to those of a similar study carried out by Dittmann et al (2016) for Dome Fuji, Dronning Maud Land (DML), another deep ice core drilling site, where a 1-year series of combined stable isotope and precipitation data is available. In both studies exactly the same methods were used for calculation of transport pathways and isotopic fractionation as well as for synoptic analysis, which is highly valuable as often past studies have site-specific approaches, making comparisons very challenging.…”

“…At the deep-drilling site Dome Fuji, while warm air advection combined with orographic lifting sometimes was not sufficient for precipitation formation, it did cause the removal of the prevalent temperature inversion layer by cloud formation that increased the downward long-wave radiation and by turbulent mixing (Enomoto et al, 1998;Hirasawa et al, 2000). Also, increased amounts of diamond dust can be observed after a synoptic snowfall event when moisture levels are still higher than on average (Hirasawa et al, 2013;Dittmann et al, 2016;Schlosser et al, 2016). Dittmann et al (2016) analyzed the only other daily precipitation / stable isotope ratio data set available in the interior of Antarctica, which was created in 2003 at the Japanese deep-drilling site Dome Fuji (Fujita and Abe, 2006).…”

“…The initial isotopic composition of the vapor after the first evaporation is calculated assuming a balance between evaporation and condensation. Details about MCIM can be found in Ciais and Jouzel (1994) and Dittmann et al (2016). Figure 1 shows a histogram of daily precipitation amounts at Dome C for the period 2008-2010 derived from (a) measurements and (b) AMPS archive data.…”

“…Also, increased amounts of diamond dust can be observed after a synoptic snowfall event when moisture levels are still higher than on average (Hirasawa et al, 2013;Dittmann et al, 2016;Schlosser et al, 2016). Dittmann et al (2016) analyzed the only other daily precipitation / stable isotope ratio data set available in the interior of Antarctica, which was created in 2003 at the Japanese deep-drilling site Dome Fuji (Fujita and Abe, 2006). They investigated synoptic conditions during precipitation, estimated moisture source areas for precipitation events, and used MCIM to model the stable isotope ratios.…”

“…Vertical resolution in WRF for the study period reflected 44 levels from the surface to 10 hPa. The use of the AMPS archive data follows the methodology of a number of published studies analyzing conditions and regimes at ice core drilling sites across Antarctica (Schlosser et al, , 2010bDittmann et al, 2016).…”