Archival processes of the water stable isotope signal in East Antarctic ice cores

Abstract

Abstract. The oldest ice core records are obtained from the East Antarctic Plateau. Water isotopes are key proxies to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in trajectory-based Rayleigh distillation and isotope-enabled climate models. However, a quantitative understanding of processes potentially altering snow isotopic composition after deposition is still missing. In low-accumulation sites, such as those found in East Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretability of an ice core's isotopic composition. By combining observations of isotopic composition in vapour, precipitation, surface snow and buried snow from Dome C, a deep ice core site on the East Antarctic Plateau, we found indications of a seasonal impact of metamorphism on the surface snow isotopic signal when compared to the initial precipitation. Particularly in summer, exchanges of water molecules between vapour and snow are driven by the diurnal sublimation–condensation cycles. Overall, we observe in between precipitation events modification of the surface snow isotopic composition. Using high-resolution water isotopic composition profiles from snow pits at five Antarctic sites with different accumulation rates, we identified common patterns which cannot be attributed to the seasonal variability of precipitation. These differences in the precipitation, surface snow and buried snow isotopic composition provide evidence of post-deposition processes affecting ice core records in low-accumulation areas.

Ice Shelf Basal Melt and Influence on Dense Water Outflow in the Southern Weddell Sea

“…This analysis suggests that HSSW interacted with an older ice, formed at higher altitude than the ice that interacted with HSSW . Only very few ice cores have measured O on FRIS, but we note that O of order 40‰ are typical values recorded at depth in ice cores over the ice sheet (Casado et al, ) and that O of order 20‰ are values consistent with those recorded in an ice core near the front of FRIS (Graf et al, ). While much uncertainty exists in the spatial variability of basal O characteristics of ice, lower values of O could be associated with ice closer to the ice front (consistent with][and arguably because ice nearer the ice‐front might locally form on the ice shelf by ice compaction ; Graf et al, ).…”

What climate signal is contained in decadal- to centennial-scale isotope variations from Antarctic ice cores?

“…The width of the kernel is set by the diffusion length σ , which is site-specific and a function of depth. For modelling the time uncertainty we use the approach of Comboul et al (2014). Model parameters are the rates of missing and double-counted annual layers, which we set to match the reported time uncertainties of the isotope records.…”

“…Furthermore, we have neglected the transfer function from isotopic ratios to temperatures, and other less constrained effects that affect the isotope signal from the atmosphere to the snow (e.g. Casado et al, 2018).…”

“…However, the interpretation of isotope records in terms of local atmospheric temperatures is complicated by a multitude of processes that distort the original relationship present in precipitation (e.g. Fujita and Abe, 2006;Sjolte et al, 2011;Steen-Larsen et al, 2011;Touzeau et al, 2016;Casado et al, 2018). To a first approximation, changes in isotopic composition are only recorded in the ice if there is snowfall, while the role of water vapour exchange processes in between precipitation events is still debated (Steen-Larsen et al, 2011;Stenni et al, 2016; Published by Copernicus Publications on behalf of the European Geosciences Union.…”

“…T. Münch and T. Laepple: Timescale dependence of Antarctic isotope variations Casado et al, 2018;Ritter et al, 2016;Münch et al, 2017a). Both the seasonality and interannual variability in the seasonality of precipitation events is known to strongly affect the isotopic composition of snow layers by introducing a bias to the mean values, e.g.…”