Frontiers in Earth Science, Volume 9
 Anthology ID:
 G21175
 Month:
 Year:
 2021
 Address:
 Venue:
 GWF
 SIG:
 Publisher:
 Frontiers Media SA
 URL:
 https://gwfuwaterloo.github.io/gwfpublications/G21175
 DOI:
Surface MassBalance Gradients From Elevation and Ice Flux Data in the Columbia Basin, Canada
Ben M. Pelto

Brian Menounos
The massbalance—elevation relation for a given glacier is required for many numerical models of ice flow. Direct measurements of this relation using remotelysensed methods are complicated by ice dynamics, so observations are currently limited to glaciers where surface massbalance measurements are routinely made. We test the viability of using the continuity equation to estimate annual surface mass balance between fluxgates in the absence of in situ measurements, on five glaciers in the Columbia Mountains of British Columbia, Canada. Repeat airborne laser scanning surveys of glacier surface elevation, ice penetrating radar surveys and publicly available maps of ice thickness are used to estimate changes in surface elevation and ice flux. We evaluate this approach by comparing modeled to observed mass balance. Modeled massbalance gradients wellapproximate those obtained from direct measurement of surface mass balance, with a mean difference of +6.6 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m1"><mml:mo>±</mml:mo></mml:math> 4%. Regressing modeled mass balance, equilibrium line altitudes are on average 15 m higher than satelliteobservations of the transient snow line. Estimates of mass balance over flux bins compare less favorably than the gradients. Average mean error (+0.03 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m2"><mml:mo>±</mml:mo></mml:math> 0.07 m w.e.) between observed and modeled mass balance over flux bins is relatively small, yet mean absolute error (0.55 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m3"><mml:mo>±</mml:mo></mml:math> 0.18 m w.e.) and average modeled massbalance uncertainty (0.57 m w.e.) are large. Mass conservation, assessed with glaciological data, is respected (when estimates are within 1σ uncertainties) for 84% of flux bins representing 86% of total glacier area. Uncertainty on ice velocity, especially for areas where surface velocity is low (<10 m a −1 ) contributes the greatest error in estimating ice flux. We find that using modeled ice thicknesses yields comparable modeled massbalance gradients relative to using observations of ice thickness, but we caution against overinterpreting individual fluxbin mass balances due to large massbalance residuals. Given the performance of modeled ice thickness and the increasing availability of ice velocity and surface topography data, we suggest that similar efforts to produce massbalance gradients using modern highresolution datasets are feasible on larger scales.