Evidence of Isotopic Fractionation During Vapor Exchange Between the Atmosphere and the Snow Surface in Greenland

Abstract

Several recent studies from both Greenland and Antarctica have reported significant changes in the water isotopic composition of near‐surface snow between precipitation events. These changes have been linked to isotopic exchange with atmospheric water vapor and sublimation‐induced 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 isotope‐enabled general circulation models. Here, we present continuous measurements of the water isotopic composition in surface snow and atmospheric vapor together with near‐surface atmospheric turbulence and snow‐air latent and sensible heat fluxes, obtained at the East Greenland Ice‐Core Project drilling site in summer 2016. For two 4‐day‐long 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 δ 18 O and δD of ~2.5‰ and ~13‰, respectively. As comparison, such changes correspond to 10–20% of the magnitude of seasonal changes in interior Greenland snow pack isotopes and of the change across a glacial‐interglacial transition. Importantly, our observation and model results suggest, that sublimation‐induced fractionation needs to be included in simulations of exchanges between the vapor and the snow surface on diurnal timescales during summer cloud‐free conditions in northeast Greenland.

Microscale Rearrangement of Ammonium Induced by Snow Metamorphism

“…Post-depositional processes can strongly alter the originally deposited signal. Such processes include wind erosion (Lorius et al, 1969;Dansgaard et al, 1973), re-emission of volatile compounds from the snow surface (Lalonde et al, 2002;Röthlisberger et al, 2002;Bartels-Rausch et al, 2008), sublimation (Stichler et al, 2001), migration within the snow and firn layer (Saltzman, 1995;Wolff, 1996), and relocation during melt-water percolation (Eichler et al, 2001;Li et al, 2006;Grannas et al, 2013). With increasing global temperatures, the fate of impurities during melt events is of increasing concern (Eichler et al, 2001;Meyer and Wania, 2008;Grannas et al, 2013).…”

Moisture origin as a driver of temporal variabilities of the water vapour isotopic composition in the Lena River Delta, Siberia

“…Present-day observations of vapour and precipitation events refine the understanding of various phases of the atmospheric water cycle and their imprint on the water isotopic compositions (Galewsky et al, 2016). Such studies focus on exchange processes between the atmosphere and the Earth's surface, over open oceans (Benetti et al, 2014(Benetti et al, , 2017Bonne et al, 2019;Zannoni et al, 2019), ice sheets (Madsen et al, 2019;Steen-Larsen et al, 2014), sea ice surfaces (Bonne et al, 2019), or continents (Bastrikov et al, 2014). Other studies focus on the atmospheric transport of moisture and show that typical vapour isotopic signals can be associated with distinct patterns of moisture origins (Bonne et al, 2014(Bonne et al, , 2015Guilpart et al, 2017;Kopec et al, 2014;Steen-Larsen et al, 2013.…”

Baffin Bay sea ice extent and synoptic moisture transport drive water vapor isotope (<i>δ</i><sup>18</sup>O, <i>δ</i>D, <i>d</i>-<i>excess</i>) variability in coastal northwest Greenland

“…The improved understanding of water vapor isotopic variability granted by our Thule observations can aid the interpretation of regional ice cores. The primary drivers of isotopic changes in water vapor are likely to also drive changes in local precipitation and accumulating snow, although there are many additional processes involved in the transfer of an isotopic signature from vapor to ice core that must be considered Casado et al, 2018;Madsen et al, 2019).…”