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

• Published in: Annals of Glaciology
• Main Authors: Charalampos Charalampidis, Dirk Van As, William T. Colgan, Robert S. Fausto, Michael Macferrin, Horst Machguth
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2016
• Subjects: Greenland ice sheet; accumulation area; firn; percolation; refreezing; superimposed ice; Meteorology. Climatology; QC851-999; Greenland; Annals of Glaciology; Ice Sheet
• Online Access: https://doi.org/10.1017/aog.2016.2; https://doaj.org/article/a7dd5d0fab7840199a3c6c6c20864c13

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.