Effect of accumulation rate on water stable isotopes of near‐surface snow in inland Antarctica

Abstract

[1] Postdepositional changes in water stable isotopes in polar firn were investigated at three sites characterized by different accumulation rates along the East Antarctic ice divide near Dome Fuji. Water stable isotopes, major ion concentrations, and tritium contents of three 2-4 m deep pits were measured at high resolution (2 cm). Temporally, the snow pits cover the past 50 years with snow accumulation rates in the range of 29-41 kg m À2 a À1around Dome Fuji. Oxygen isotopic profiles in the three pits do not show annual fluctuations, but instead exhibit multiyear cycles. These multiyear cycles are lower in frequency at Dome Fuji as compared with the other two sites. Peaks of water stable isotopes in the multiyear cycles correspond to some ion concentration minima in the pits, although such relationships are not observed in coastal regions. We propose that the extremely low accumulation environment keeps the snow layer at the near surface, which result in postdepositional modifications of isotopic signals by processes such as ventilation and vapor condensation-sublimation. We estimate that oxygen isotopic ratios could be modified by >10‰ and that the original seasonal cycle could be completely overprinted under the accumulation conditions at Dome Fuji. Moreover, stake measurements at Dome Fuji suggest that the large variability in snow accumulation rate is the cause of the multiyear cycles.Citation: Hoshina, Y., K. Fujita, F. Nakazawa, Y. Iizuka, T. Miyake, M. Hirabayashi, T. Kuramoto, S. Fujita, and H. Motoyama (2014), Effect of accumulation rate on water stable isotopes of near-surface snow in inland Antarctica,

Densification of layered firn in the ice sheet at Dome Fuji, Antarctica

“…Clearly, we must document these in order to understand processes related to major ions. For example, the depth-dependent variation of Mg 2+ is always very similar to Na + in the shallowest 4 m deep pit at DF sites (Hoshina and others, 2014) until depths close to pore close-off ( Fig. 10; Table 5).…”

“…Here, we document the major features of these matrices. Commonly, for the three sites, Na Hoshina and others, 2014). This will be confirmed later (Fig.…”

Experimental observation of transient <i>δ</i><sup>18</sup>O interaction between snow and advective airflow under various temperature gradient conditions

“…The snow exposed for a relatively short time to vapour snow exchange would result in higher spatial variability compared to longer exposure. However, the effects of snow ventilation on isotopic composition may become more important as the accumulation rate of the snow decreases (< 50 mm a −1 ), such that snow remains in the nearsurface ventilated zone for many years (Waddington et al, 2002;Hoshina et al, 2014Hoshina et al, , 2016. As the snow remains for a longer time in the near-surface ventilated zone, a larger δ 18 O exchange will occur between snow and atmospheric vapour.…”

“…Several factors affect the vapour and snow isotopic composition, which give rise to ice-core isotopic composition, starting from the process of evaporation in the source region, transportation of the air mass to the top of the ice sheet and post-depositional processes (Craig and Gordon, 1964;Merlivat and Jouzel, 1979;Johnsen et al, 2001;Ciais and Jouzel, 1994;Jouzel and Merlivat, 1984;Jouzel et al, 2003;Helsen et al, 2005Helsen et al, , 2006Helsen et al, , 2007Cuffey and Steig, 1998;Krinner and Werner, 2003). Mechanical processes such as mixing, seasonal scouring or spatial redistribution of snow can alter seasonal and annual records (Fisher et al, 1983;Hoshina et al, 2014). Post-depositional processes associated with wind scouring and snow redistribution are known to introduce a "postdepositional noise" in the surface snow.…”

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

“…These local effects reduce the signal /noise ratio, and then only stacking a series of snow pits can eliminate this local 45 variability and yield information relevant to recent climate variations (Altnau et al, 2015;Ekaykin et al, 2014;Ekaykin et al, 2002;Fisher and Koerner, 1994;Hoshina et al, 2014). This concern is particularly significant in central regions of east Antarctica characterized by very low accumulation rates (< 100 mm w.e.…”