Boundary layer stability acts to ballast the mass of the Greenland Ice Sheet

Monday, 15 December 2014: 10:50 AM
Max B Berkelhammer1, David C Noone2,3, Hans Christian Steen-Larsen4, Michael O'Neill5, Adriana Raudzens Bailey6,7, Christopher Cox3,4 and David P Schneider8, (1)University of Illinois at Chicago, Chicago, IL, United States, (2)Oregon State University, College of Earth, Ocean and Atmospheric Sciences, Corvallis, OR, United States, (3)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (4)University of Colorado, Boulder, CO, United States, (5)NOAA Boulder, Global Monitoring Division, Boulder, CO, United States, (6)University of Colorado, Cooperative Institute for Research in Environmental Sciences and Dept. of Atmospheric and Oceanic Sciences, Boulder, CO, United States, (7)Dept Atmospheric & Oceanic Sci, Boulder, CO, United States, (8)National Center for Atmospheric Research, Boulder, CO, United States
The mass of the Greenland Ice Sheet has been reduced over recent decades as a consequence of warming, the impact of which is already detectable on global sea level. However, temperature projections suggest that at interior high-altitude sites on the ice it could be decades or more before warming forces these regions to transition from a dry to wet snow facies. Shifts in boundary layer dynamics, including atmosphere-ice sheet hydrological exchange and cloud radiative forcing could expedite or delay this transition. These processes are important with respect to future ice sheet stability, yet they remain difficult to constrain. Using continuous in situ measurements of vertical profiles of the isotopic composition of water vapor at Summit Camp, the highest observatory on the ice sheet, we document the presence of a hydrologic balance between surface sublimation and condensation fluxes. This exists because of a nearly persistent temperature inversion, which hinders the efficiency with which surface water vapor mixes into the free atmosphere. In the presence of a strong temperature inversion, fog and ice particles form near the ice-atmosphere interface from surface moisture fluxes. When this condensate precipitates on or settles to the surface, it ballasts the ice sheet’s mass. A decade-long trend towards lower annual accumulation at Summit may therefore reflect continuous replacement of the near surface atmosphere due to reduced atmospheric stability. If this tendency toward destabilization continues, it could accelerate mass loss at interior sites on the ice sheet. The role of boundary layer stability in ice sheet hydrological budgets discussed here is applicable beyond the accumulation zone of the Greenland Ice Sheet.