3 research outputs found
Evidence of Isotopic Fractionation During Vapor Exchange Between the Atmosphere and the Snow Surface in Greenland
Several recent studies from both Greenland and Antarctica have reported significant changes in the water isotopic composition of nearâsurface snow between precipitation events. These changes have been linked to isotopic exchange with atmospheric water vapor and sublimationâinduced fractionation, but the processes are poorly constrained by observations. Understanding and quantifying these processes are crucial to both the interpretation of ice core climate proxies and the formulation of isotopeâenabled general circulation models. Here, we present continuous measurements of the water isotopic composition in surface snow and atmospheric vapor together with nearâsurface atmospheric turbulence and snowâair latent and sensible heat fluxes, obtained at the East Greenland IceâCore Project drilling site in summer 2016. For two 4âdayâlong time periods, significant diurnal variations in atmospheric water isotopologues are observed. A model is developed to explore the impact of this variability on the surface snow isotopic composition. Our model suggests that the snow isotopic composition in the upper subcentimeter of the snow exhibits a diurnal variation with amplitudes in δ18O and δD of ~2.5â° and ~13â°, respectively. As comparison, such changes correspond to 10â20% of the magnitude of seasonal changes in interior Greenland snow pack isotopes and of the change across a glacialâinterglacial transition. Importantly, our observation and model results suggest, that sublimationâinduced fractionation needs to be included in simulations of exchanges between the vapor and the snow surface on diurnal timescales during summer cloudâfree conditions in northeast Greenland
A portable lightweight in situ analysis (LISA) box for ice and snow analysis
There are enormous costs involved in transporting snow and ice samples to home laboratories for âsimpleâ analyses in order to constrain annual layer thicknesses and identify accumulation rates of specific sites. It is well known that depositional noise, incurred from factors such as wind drifts, seasonally biased deposition and melt layers can influence individual snow and firn records and that multiple cores are required to produce statistically robust time series. Thus, at many sites, core samples are measured in the field for densification, but the annual accumulation and the content of chemical impurities are often represented by just one core to reduce transport costs. We have developed a portable âlightweight in situ analysisâ (LISA) box for ice, firn and snow analysis that is capable of constraining annual layers through the continuous flow analysis of meltwater conductivity and hydrogen peroxide under field conditions. The box can run using a small gasoline generator and weighs less than 50âkg. The LISA box was tested under field conditions at the East Greenland Ice-core Project (EastGRIP) deep ice core drilling site in northern Greenland. Analysis of the top 2âm of snow from seven sites in northern Greenland allowed the reconstruction of regional snow accumulation patterns for the 2015â2018 period (summer to summer)