Abstract
ABSTRACTWe present in situ firn temperatures from the extreme 2012 melt season in the southwestern lower accumulation area of the Greenland ice sheet. The upper 2.5 m of snow and firn was temperate during the melt season, when vertical meltwater percolation was inefficient due to a ~5.5 m thick ice layer underlying the temperate firn. Meltwater percolation and refreezing beneath 2.5 m depth only occurred after the melt season. Deviations from temperatures predicted by pure conductivity suggest that meltwater refroze in discrete bands at depths of 2.0–2.5, 5.0–6.0 and 8.0–9.0 m. While we find no indication of meltwater percolation below 9 m depth or complete filling of pore volume above, firn at 10 and 15 m depth was respectively 4.2–4.5°C and 1.7°C higher than in a conductivity-only simulation. Even though meltwater percolation in 2012 was inefficient, firn between 2 and 15 m depth the following winter was on average 4.7°C warmer due to meltwater refreezing. Our observations also suggest that the 2012 firn conditions were preconditioned by two warm summers and ice layer formation in 2010 and 2011. Overall, firn temperatures during the years 2009–13 increased by 0.6°C.
Highlights
In recent years, the air or surface temperatures of the Greenland ice sheet have increased (Van As, 2011; Hall and others, 2013), contributing to accelerated mass loss (Shepherd and others, 2012)
In early June, meltwater percolation within the snow and firn is readily identifiable as a coherent warming front in all panels of Figure 3
Firn temperature measurements from the lower accumulation area (LAA) of the Southwestern Greenland ice sheet suggest that during the 2012 extreme melt season, meltwater percolation below 2.5 m depth was suppressed due to superimposed ice lenses of ∼5.5 m thickness previously generated in recent years
Summary
The air or surface temperatures of the Greenland ice sheet have increased (Van As, 2011; Hall and others, 2013), contributing to accelerated mass loss (Shepherd and others, 2012). Increases in surface runoff accounted for two-thirds of ice-sheet mass loss between 2009 and 2012 (Enderlin and others, 2014). During the summer of 2012 the atmosphere was exceptionally warm over the ice sheet (Bennartz and others, 2013; Tedesco and others, 2013), resulting in an exceptional surface melt extent that was unprecedented during the observational period. Summit was relatively warm throughout the summer of 2012, with the highest June–August (JJA) average air temperature (−11.4°C) observed since 1994 (Hanna and others, 2014). Ice core evidence suggests that melting at Summit had previously not occurred since 1889 (Clausen and others, 1988; Keegan and others, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
