Tritium Records to Trace Stratospheric Moisture Inputs in Antarctica

Abstract

Better assessing the dynamic of stratosphere‐troposphere exchange is a key point to improve our understanding of the climate dynamic in the East Antarctica Plateau, a region where stratospheric inputs are expected to be important. Although tritium (3H or T), a nuclide naturally produced mainly in the stratosphere and rapidly entering the water cycle as HTO, seems a first‐rate tracer to study these processes, tritium data are very sparse in this region. We present the first high‐resolution measurements of tritium concentration over the last 50 years in three snow pits drilled at the Vostok station. Natural variability of the tritium records reveals two prominent frequencies, one at about 10 years (to be related to the solar Schwabe cycles) and the other one at a shorter periodicity: despite dating uncertainty at this short scale, a good correlation is observed between 3H and Na+ and an anticorrelation between 3H and δ18O measured on an individual pit. The outputs from the LMDZ Atmospheric General Circulation Model including stable water isotopes and tritium show the same 3H‐δ18O anticorrelation and allow further investigation on the associated mechanism. At the interannual scale, the modeled 3H variability matches well with the Southern Annular Mode index. At the seasonal scale, we show that modeled stratospheric tritium inputs in the troposphere are favored in winter cold and dry conditions.

A Comparison of 36Cl Nuclear Bomb Inputs Deposited in Snow From Vostok and Talos Dome, Antarctica, Using the 36Cl/Cl− ratio

“…Such similarities are also evidenced when comparing Na + concentration to 10 Be concentration along the same snow pit (Baroni et al, ; Figures c and d) and have likewise been identified with 3 H (Fourré et al, ). It has been proposed that these periodicities within the 3‐ to 7‐year band result from a modulation of atmospheric circulation in the troposphere, induced either by the Antarctic Circumpolar Wave (ACW; Baroni et al, ) or by the Southern Annular Mode (SAM; Fourré et al, ). In this scenario, the coupling between 10 Be/ 3 H and Na + is seen as an indirect link related to the influence of modes of atmospheric circulation (ACW or SAM) on stratospheric inputs (Baroni et al, ; Fourré et al, ).…”

“… 36 Cl evolution through time (a) from this study (green line) compared to 36 Cl concentration of Vostok in another snow pit dug and measured 10 years prior to our study (Delmas et al, , in black) and also in comparison with 137 Cs (b) (Baroni et al, ) and 3 H (c) (Fourré et al, ) from the same snow pit. The 36 Cl model simulation is also represented, with the orange line reflecting the values of advection and diffusion proposed by Delmas et al, , the red line illustrating new parameters fitting better with our 36 Cl values, and the purple line representing a reduced diffusion coefficient compared to the other two simulations.…”

“…These differences are also visible with tritium, which is related to the water vapor cycle in the stratosphere. Tritium is another marker of nuclear testing whose concentration tends toward prebomb concentrations soon after the end of the tests (Fourré et al, , Figure c). Migration of H 36 Cl within the first meters of the Vostok snow pit has also been confirmed by the 10 Be/ 36 Cl ratio.…”

“…The total balance over the 1962-1998 period is, however, 27% higher in our study than in Delmas et al (2004). This may be explained by uncertainties associated with the dating of the snow pit in Delmas et al (2004), whose chronology is based on the 137 Cs peaks only, while we use these time markers in addition to markers of two volcanic eruptions (the 1963 Agung event and the prior to our study (Delmas et al, 2004, in black) and also in comparison with 137 Cs (b) (Baroni et al, 2011) and 3 H (c) (Fourré et al, 2018) Delmas et al (2004) in their study of 1997 and 1998 Vostok snow pits, this may also be explained by concentration profile differences along different snow pits from the same site, even if the pits are dug close to each other. This may also highlight the fact that anthropogenic 36 Cl is still being deposited in Vostok.…”

“…The studied snow pit is located near the Vostok station, on the East Antarctic Plateau (78°S, 106°E, 3,488 m, −55°C on average; see Figure 1 for location). 10 Be, major ions, radio activity (beta and gamma), and 3 H and water oxygen isotopes have previously been measured (Baroni et al, 2011;Fourré et al, 2018;Winkler et al, 2013) in this snow pit. The mean accumulation rate is 1.96 g cm −2 year −1 water equivalent (Ekaykin et al, 2004).…”