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 records are key to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all the processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in Rayleigh distillation and isotope enabled climate models. However, a quantitative understanding of processes potentially altering the snow isotopic composition after the deposition is still missing. 5In low accumulation sites, such as those found in Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretation of isotopic composition.Here, we combine observations of isotopic composition in the vapour, the precipitation, the surface snow and the buried snow from Dome C, a deep ice core site on the East Antarctic Plateau. At the seasonal scale, we suggest a significant impact of 10 metamorphism on surface snow isotopic signal compared to the initial precipitation signal. Particularly, in summer, exchanges of water molecules between vapour and snow are driven by the sublimation/condensation cycles at the diurnal scale. Using highly resolved isotopic composition profiles from pits in five Antarctic sites, we identify common patterns, despite different accumulation rates, which cannot be attributed to the seasonal variability of precipitation. Altogether, the difference in the signals observed in the precipitation, surface snow and buried snow isotopic composition constitute evidences of post-deposition 15 processes affecting ice core records in low accumulation areas. 1The Cryosphere Discuss., https://doi

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, ).…”

Nonequilibrium Fractionation During Ice Cloud Formation in iCAM5: Evaluating the Common Parameterization of Supersaturation as a Linear Function of Temperature

“…By using the isotope ratios of precipitation from iCAM5, we also neglect potential postdepositional processes. Recent studies from Greenland and Antarctica show that isotopic exchanges between snow and water vapor (Steen‐Larsen et al, ), fractionation during sublimation (Madsen et al, ; Ritter et al, ), and snow metamorphism (Casado et al, ) may alter the isotope ratios in surface snow, especially at low accumulation sites. Due to the snow depth limit of H max =1m snow water equivalent in our version of CLM4 (see section ), the simulated snow pack mainly reflects the initial isotopic composition instead of the signal from precipitation, and it is not possible to meaningfully account for postdepositional processes.…”

Snowfall and Water Stable Isotope Variability in East Antarctica Controlled by Warm Synoptic Events

“…The lower correlation value might be due to (1) the smoothing of high frequencies caused by the CFA technique used to measure this core (Gkinis et al, 2011; Holme et al, 2018) and/or (2) difference in snow deposition, as the short core was taken ~200 m away from the snow pits. Snow at low‐accumulation plateau sites exchanges isotopes with underlying snow through diffusion (Casado et al, 2018) and can be deposited in patches inducing differences in layer thicknesses related to surface roughness (Picard et al, 2019). These processes increase horizontal variability and influence the mean δ 18 O. Münch et al (2016) also show that stratigraphic noise lowers the correlation of two δ 18 O series in a few meters at Kohnen Station in Dronning Maud Land (dropping from r = 1.0 to r = 0.5 in 10 m, then plateauing at 0.5 correlation), albeit the accumulation at Kohnen Station (64 mm w.eq.…”

“…Advances in analytical methods and introduction of Cavity Ring‐Down Spectroscopy have allowed precise measurements of δ 18 O and δD with a decreased analysis time, leading to a substantial increase in resolution (Gupta et al, 2009). However, archival limitations due to intermittency of precipitation events and loss of short periodicity signal due to postdeposition processes are particularly important in low‐accumulation areas, such as the East Antarctic Plateau (Casado et al, 2018, 2019). Deep ice cores drilled on the East Antarctic Plateau provide climate information over long timescales with a low (>50 year) resolution, complementing the short instrumental record (Ekaykin et al, 2017).…”