Deuterium excess in recent Antarctic snow

Abstract

Deuterium excess (d = δD ‐ 8 * δ18O) values in surface snow are presented for central and east Antarctica. The samples are primarily from Soviet, French, and Australian traverses. The d values exhibit a large change going from coastal sites to high‐altitude sites on the ice sheet. The d values are relatively constant at 3 to 6‰ from the coast to an altitude of 2500 m, and at higher elevations d increases steadily to values of 16 to 18‰ at Vostok and Plateau Station. The data is modeled as d versus δD using the kinetic Rayleigh model for isotopes in precipitation developed by Jouzel and Merlivat. The model accounts for kinetic fractionation during evaporation into undersaturated air over the ocean and during snow formation in <−10°C clouds where vapor is supersaturated with respect to snow. The overall pattern of d versus δD can be fit well with a supersaturation function which increases linearly with decreasing temperature and which predicts reasonable values of the supersaturation. Vapor originating from 20° to 60°S was tested with different supersaturation functions. The data could only be fit with moisture originating from 30° to 40°S, indicating that these latitudes are the main source of vapor for snow falling in Antarctica. The conclusion of a mid‐latitude vapor source for polar snow agrees with the analysis of d and δ18O seasonal cycles in Greenland snow performed by Johnsen and coworkers. The model was also tested with moisture simultaneously originating from all latitudes from 30°S to the Antarctic coast. The addition of up to 20% of moisture evaporated from latitudes south of 50°, and 5% from latitudes south of 60°, is compatible with low d values occasionally observed in snow near the coast. The conclusion of a “local moisture” effect for coastal and near coastal (<2000 m elevation) snowfall supports a similar conclusion by Saigne and Legrand from their analysis of methanesulphonic acid in Antarctic snow. Finally, the effects of changes in the sea surface temperature and changes in oceanic humidity on the d values observed in Antartic snow are greatly modified during the precipitation process. Hence the interpretation of d values in ice cores should be done in the context of a precipitation model.

A late-glacial high-resolution site and source temperature record derived from the EPICA Dome C isotope records (East Antarctica)

“…Two factors may account for the 6^7x higher excess levels at Vostok compared to Dome C: 1. a larger kinetic e¡ect at snow formation due to colder conditions at Vostok than Dome C, as suggested by Petit et al [51] ; 2. di¡erent moisture transport patterns with a larger contribution of remote low-latitude moisture transported at higher altitudes to the more inland site of Vostok. General circulation models indicate that low-latitude moisture is transported at higher altitudes to the inland plateau of East Antarctica, with a progressive warming of the mean moisture source from the Antarctic coast toward the central plateau [45].…”

New insights into the climatic signal from firn cores at the northern Antarctic Peninsula

“…The most frequent dexcess values found in the firn cores (3‰ -6‰) are in agreement with a strong coastal influence scenario as 5 determined by Petit et al (1991), implying that the dexcess relates to rh and SST of the humidity source and not to surface air temperature (Jouzel et al, 2013). Saigne and Legrand (1987), postulated that rh conditions prevailing at the sea surface have an important effect on the dexcess signal of precipitation below 2000 m a.s.l in the study region.…”

Atmospheric signals and characteristics of accumulation in Dronning Maud Land, Antarctica

“…One example of particular concern in this study is the effect of increasing the spatial resolution of the model. It has been seen that model precipitation depends strongly on the ability of a model to represent orography [Chen et Observational studies suggest a winter source near the sea ice edge at 55øS [Karo, 1978], while model studies [Petit et al, 1991] suggest a midlatitude origin 30ø-40øS. Bromwich [1988] suggests that this discrepancy is associated with the nature of the analysis methodology; namely, the moisture budget approach considers net flux for an atmospheric volume, while an isotopic model approach indicates the history of a conglomerate of individual parcels.…”