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TitleField-calibrated model of melt, refreezing, and runoff for polar ice caps: Application to Devon Ice Cap
AuthorMorris, R M; Mair, D W F; Nienow, P W; Bell, C; Burgess, D O; Wright, A P
SourceJournal of Glaciology vol. 119, no. 9, 2014 p. 1995-2012,
Alt SeriesEarth Sciences Sector, Contribution Series 20130371
PublisherInternational Glaciological Society
Mediapaper; on-line; digital
File formatpdf
NTS48E/13; 48E/14; 48H/03; 48H/04; 48H/05; 48H/06
AreaDevon Ice Cap
Lat/Long WENS -83.5000 -82.0000 75.5000 74.7500
Subjectsrunoff; glaciers; modelling; snow; meltwater channels; ice; ice conditions; temperature; mass balance; meltwater; firn; densities; spatial variability
Illustrationslocation maps; digital elevation models; graphs
ProgramEssential Climate Variable Monitoring, Climate Change Geoscience
AbstractUnderstanding the controls on the amount of surface meltwater that refreezes, rather than becoming runoff, over polar ice masses is necessary for modeling their surface mass balance and ultimately for predicting their future contributions to global sea level change. We present a modified version of a physically based model that includes an energy balance routine and explicit calculation of near-surface meltwater refreezing capacity, to simulate the evolution of near-surface density and temperature profiles across Devon Ice Cap in Arctic Canada. Uniquely, our model is initiated and calibrated using high spatial resolution measurements of snow and firn densities across almost the entire elevation range of the ice cap for the summer of 2004 and subsequently validated with the same type of measurements obtained during the very different meteorological conditions of summer 2006. The model captures the spatial variability across the transect in bulk snowpack properties although it slightly underestimates the flow of meltwater into the firn of previous years. The percentage of meltwater that becomes runoff is similar in both years; however, the spatial pattern of this melt-runoff relationship is different in the 2 years. The model is found to be insensitive to variation in the depth of impermeable layers within the firn but is very sensitive to variation in air temperature, since the refreezing capacity of firn decreases with increasing temperature. We highlight that the sensitivity of the ice cap's surface mass balance to air temperature is itself dependent on air temperature.
Summary(Plain Language Summary, not published)
High elevation regions (>1200 m a.s.l.) of ice caps in the Canadian high Arctic consist of firn which is a porous medium that develops from snow that has accumulated across these regions, but has not experienced sufficient summer warmth to melt completely. During climate warming scenarios, the density of near surface firn increases due to the downward percolation and refreezing of excessive amounts of melt water generated at the surface. This process can lead to decreased water storage capacity, and have a significant effect on the overall mass balance of ice caps as the polar regions continue to warm. Using validation data from the Devon ice cap, Nunavut, model results from this study indicate that under linear increasing air temperature scenarios, the overall ice cap mass balance will experience exponential rates of mass loss partially as a consequence of increased runoff due to reduced storage capacity of high elevation firn. This has important consequences for predicting how ice caps will respond to climate warming, and their associated impact on global sea-level rise.