Seasonal Deuterium Excess Variations of Precipitation at Summit, Greenland, and their Climatological Significance

Abstract

The hydrogen and oxygen isotopic composition of ice cores from Summit, Greenland, has provided invaluable information about variations in past climate. However, interpretations of these isotopic data have been made despite a paucity of direct isotopic studies of Summit precipitation. We provide insight to such interpretations by examining the annual cycle of deuterium excess (d‐excess) in precipitation samples from Summit and by considering the climatic controls on the annual cycle. Precipitation was collected daily from July 2011 to September 2014 at heights of 1, 2, and 4 m. The isotopic composition of precipitation sampled at 4 m above the snow surface is free of contamination from blowing snow. Precipitation d‐excess is high in the summer and low in the winter, a pattern opposite to that found at most high‐latitude locations, where summer d‐excess is low relative to winter. Low winter d‐excess values at Summit can be explained by varying degrees of Rayleigh distillation of moisture sourced from isotopically similar marine sources. However, the observed summer d‐excess maximum at Summit is anomalously high compared with other Arctic locations, and we propose that this is due to high d‐excess moisture contributed by sublimation of surface snow on the Greenland Ice Sheet. We demonstrate the plausibility of this hypothesis through simple isotopic mass balance calculations, analyses of cloud heights, and back trajectories to identify moisture sources. We show that Rayleigh distillation, sublimation, and the phase of the d‐excess annual cycle are all important factors that should be considered in ice core d‐excess interpretations.

Influence of Summer Sublimation on δD, δ18O, and δ17O in Precipitation, East Antarctica, and Implications for Climate Reconstruction From Ice Cores

“…Observations of water vapor isotopes at Summit (Greenland) carried out by Berkelhammer et al (2016) suggest that moisture sublimated from the ice sheet surface can recondense on fog particles, and ultimately returns to the ice surface under stable conditions associated with temperature inversion during summertime nights. More recently, high values of d-excess in summer precipitation and low values in winter precipitation at Summit (Greenland) were observed by Kopec et al (2019), a pattern opposite to that found at most high-latitude locations. They propose that the observed summer d-excess maximum at Summit is due to the contribution of high d-excess moisture from sublimation of surface snow on the Greenland Ice Sheet.…”

Precipitation and ice core δD-δ<sup>18</sup>O line slopes and their climatological significance

“…Rayleigh distillation alters d-excess through a nonlinear evolution of the δD-δ 18 O trajectory as moisture in an air mass progressively condenses and rains out (Craig, 1961;Majoube, 1971;Ciais and Jouzel, 1994;Dutsch et al, 2017). Kopec et al (2019) demonstrated that Rayleigh distillation can help explain the relatively low d-excess values in winter Summit precipitation. On the other hand, Summit d-excess in the summer is extraordinarily high, which they explained via moisture contribution from sublimation of surface snow on the Greenland Ice Sheet along the air mass transport path.…”

“…Despite the depth of information we have learned from these measurements in ice cores, a recent study has shown that there may be more to the story than we presently understand, particularly regarding the deuterium excess records. While Feng et al (2009) demonstrated that almost all sites in the mid-to high-latitudes of the Northern (and Southern) hemisphere exhibit an out-of-phase relationship between δD and d-excess, and the mechanisms controlling this pattern are relatively well understood, Kopec et al (2019) recently reported a nearly inphase relationship between δD and d-excess of event-based precipitation measurements at Summit, Greenland. This unique relationship requires additional investigation into the mechanisms controlling the water isotope record, primarily d-excess, at Summit.…”

“…This unique relationship requires additional investigation into the mechanisms controlling the water isotope record, primarily d-excess, at Summit. In addition to changing marine moisture sources as a major control of d-excess, to explain the unique d-excess variations at Summit, Kopec et al (2019) discussed two mechanisms: 1) Rayleigh distillation and 2) sublimation as a source of water vapor for precipitation. Rayleigh distillation alters d-excess through a nonlinear evolution of the δD-δ 18 O trajectory as moisture in an air mass progressively condenses and rains out (Craig, 1961;Majoube, 1971;Ciais and Jouzel, 1994;Dutsch et al, 2017).…”

“…On the other hand, Summit d-excess in the summer is extraordinarily high, which they explained via moisture contribution from sublimation of surface snow on the Greenland Ice Sheet along the air mass transport path. Water vapor sourced from sublimation has a relatively high d-excess and Kopec et al (2019) demonstrated that this mechanism provides a significant proportion of moisture to summer precipitation at Summit. They considered sublimation to be especially important for ice core interpretations because this vapor provides a high d-excess moisture source, in addition to vapor evaporated from a warm sea surface, to the total precipitation.…”