Thermal tracing of retained meltwater in the lower accumulation area of the Southwestern Greenland ice sheet

We 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. DOI: https://doi.org/10.1017/aog.2016.2 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-126149 Published Version Originally published at: Charalampidis, Charalampos; Van As, Dirk; Colgan, William T; Fausto, Robert S; Macferrin, Michael; Machguth, Horst (2016). Thermal tracing of retained meltwater in the lower accumulation area of the Southwestern Greenland ice sheet. Annals of Glaciology:1-10. DOI: https://doi.org/10.1017/aog.2016.2 Thermal tracing of retained meltwater in the lower accumulation area of the Southwestern Greenland ice sheet Charalampos CHARALAMPIDIS, Dirk VAN AS, William T. COLGAN, Robert S. FAUSTO, Michael MACFERRIN, Horst MACHGUTH Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, 1350 Copenhagen K, Denmark E-mail: [email protected] Department of Earth Sciences, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden Department of Earth and Space Sciences and Engineering, York University, 4700, Keele Street, M3J 1P3 Toronto, Canada Cooperative Institute for Research in Environmental Sciences (CIRES), 216 UCB, University of Colorado Boulder, Boulder, CO 80309, USA Arctic Technology Centre (ARTEK), Technical University of Denmark, Brovej, byg. 118, 2800, Kgs Lyngby, Denmark ABSTRACT. We present in situ firn temperatures from the extreme 2012 melt season in the southwestern We 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.