Hypsometric amplification and routing moderation of Greenland ice sheet meltwater release

• Published in: The Cryosphere
• Main Authors: D. van As, A. Bech Mikkelsen, M. Holtegaard Nielsen, J. E. Box, L. Claesson Liljedahl, K. Lindbäck, L. Pitcher, B. Hasholt
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2017
• Subjects: Environmental sciences; GE1-350; Geology; QE1-996.5; Greenland; Ice Sheet; The Cryosphere
• Online Access: https://doi.org/10.5194/tc-11-1371-2017; https://doaj.org/article/ceac16c34bcd494d9a6641e050f435b1

Concurrent ice sheet surface runoff and proglacial discharge monitoring are essential for understanding Greenland ice sheet meltwater release. We use an updated, well-constrained river discharge time series from the Watson River in southwest Greenland, with an accurate, observation-based ice sheet surface mass balance model of the ∼ 12 000 km 2 ice sheet area feeding the river. For the 2006–2015 decade, we find a large range of a factor of 3 in interannual variability in discharge. The amount of discharge is amplified ∼ 56 % by the ice sheet's hypsometry, i.e., area increase with elevation. A good match between river discharge and ice sheet surface meltwater production is found after introducing elevation-dependent transit delays that moderate diurnal variability in meltwater release by a factor of 10–20. The routing lag time increases with ice sheet elevation and attains values in excess of 1 week for the upper reaches of the runoff area at ∼ 1800 m above sea level. These multi-day routing delays ensure that the highest proglacial discharge levels and thus overbank flooding events are more likely to occur after multi-day melt episodes. Finally, for the Watson River ice sheet catchment, we find no evidence of meltwater storage in or release from the en- and subglacial environments in quantities exceeding our methodological uncertainty, based on the good match between ice sheet runoff and proglacial discharge.