Greenland Ice Sheet surface melt captured by high frequency water vapor isotopes measurements at Thule
Abstract
The summer of 2019 was marked by an extensive early onset of surface melt of the Greenland Ice Sheet, which is part of a larger trend of increasing melt over time with a warming climate. Given the large spatial extent of melt in recent years, the flux of water vapor away from the ice (by evaporation of meltwater at the surface and sublimation of snow and ice) is an increasingly important component of the ice sheet's mass balance that now merits investigation and quantification. The isotopic composition of water vapor, particularly the deuterium excess, provides a powerful tool to investigate the changing hydrologic cycle around the ice sheet. In this study, we present measurements of hydrogen (δD) and oxygen (δ18O) isotopic ratios and deuterium excess (d-excess or d; d = δD - 8δ18O) of water vapor from Thule, NW Greenland. We focus on how the extent and timing of surface melt in the summers of 2015, 2017, 2018 and 2019 affect the isotopic composition of water vapor. A dominant pattern in the data is the isotopic difference of water vapor blowing off the Greenland Ice Sheet (GIS) to the east and from northern Baffin Bay to the west. Easterly winds bring water vapor off the GIS with significantly higher d-excess than westerly winds off Baffin Bay. This is consistent with expectations that water vapor sourced from sublimation of snow and ice and/or evaporation of meltwater has relatively high d-excess compared to moisture sourced from cold ocean waters in Baffin Bay. When examining water vapor only blowing off the ice sheet (i.e., when winds are from the east), we find that increases in the GIS surface melt produce significantly higher d-excess at Thule as more moisture is sourced from the GIS itself. The magnitude of the surface melt extent effect on d-excess is comparable to, if not greater than, other factors that also influence sublimation and evaporation, including temperature, relative humidity, and wind speed. Using these water vapor measurements, we quantify the water vapor flux from the ice sheet via atmospheric transport, as well as partition moisture sourced from sublimation of snow/ice and meltwater evaporation. Our results demonstrate that, at least under certain wind regimes (i.e. katabatic winds from the interior GIS to the coast), significant water content is lost from the ice sheet by atmospheric transport.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP22A..06K
- Keywords:
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- 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSES;
- 1041 Stable isotope geochemistry;
- GEOCHEMISTRY;
- 1655 Water cycles;
- GLOBAL CHANGE;
- 1833 Hydroclimatology;
- HYDROLOGY