Abstract
ABSTRACTGlaciers spanning large altitudinal ranges often experience different climatic regimes with elevation, creating challenges in acquiring mass-balance and climate observations that represent the entire glacier. We use mixed methods to reconstruct the 1991–2014 mass balance of the Kahiltna Glacier in Alaska, a large (503 km2) glacier with one of the greatest elevation ranges globally (264–6108 m a.s.l.). We calibrate an enhanced temperature index model to glacier-wide mass balances from repeat laser altimetry and point observations, finding a mean net mass-balance rate of −0.74 mw.e. a−1( ± σ = 0.04, std dev. of the best-performing model simulations). Results are validated against mass changes from NASA's Gravity Recovery and Climate Experiment (GRACE) satellites, a novel approach at the individual glacier scale. Correlation is strong between the detrended model- and GRACE-derived mass change time series (R2 = 0.58 and p ≪ 0.001), and between summer (R2 = 0.69 and p = 0.003) and annual (R2 = 0.63 and p = 0.006) balances, lending greater confidence to our modeling results. We find poor correlation, however, between modeled glacier-wide balances and recent single-stake monitoring. Finally, we make recommendations for monitoring glaciers with extreme altitudinal ranges, including characterizing precipitation via snow radar profiling.
Highlights
Alaska is home to seven major glacierized mountain ranges, with topography spanning from sea level to 6190 m a.s.l. at the summit of Denali, North America’s highest mountain
Larsen and others (2015) used repeat laser altimetry data to derive a mass change of −75 ± 11 Gt a−1 for all Alaska glaciers between 1994 and 2013, an estimate that best represents our current state of knowledge
Combining enhanced temperature index modeling with new ground observations and laser altimetry estimates, and validating against a simple spatially downscaled Gravity Recovery and Climate Experiment (GRACE)
Summary
Alaska is home to seven major glacierized mountain ranges, with topography spanning from sea level to 6190 m a.s.l. at the summit of Denali, North America’s highest mountain. Alaska glacier runoff constitutes an estimated 38% (Neal and others, 2010) to 47% (Beamer and others, 2016) of the total annual land-to-ocean freshwater flux into the Gulf of Alaska, acting as a principal driver of the Alaska Coastal Current that delivers crucial nutrients and freshwater to coastal ecosystems (Royer, 1981). In their recent study, Larsen and others (2015) used repeat laser altimetry data to derive a mass change of −75 ± 11 Gt a−1 for all Alaska glaciers between 1994 and 2013, an estimate that best represents our current state of knowledge. Uncertainty in their estimate was largely due to extrapolation from surveyed to unsurveyed glaciers, given substantial glacier-to-glacier variability in mass loss due to the wide range of glacier types (tidewater, lake-, and land-terminating), sizes, and geometries
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