Ice flow modelling to constrain the surface mass balance and ice discharge of San Rafael Glacier, Northern Patagonia Icefield

Gabriela Collao-Barrios,Fabien Gillet-Chaulet,Jérémie Mouginot,Gino Casassa,Etienne Berthier,Inés Dussaillant,Eric Rignot,Vincent Favier

doi:10.1017/jog.2018.46

Abstract

ABSTRACTWe simulate the ice dynamics of the San Rafael Glacier (SRG) in the Northern Patagonia Icefield (46.7°S, 73.5°W), using glacier geometry obtained by airborne gravity measurements. The full-Stokes ice flow model (Elmer/Ice) is initialized using an inverse method to infer the basal friction coefficient from a satellite-derived surface velocity mosaic. The high surface velocities (7.6 km a−1) near the glacier front are explained by low basal shear stresses (<25 kPa). The modelling results suggest that 98% of the surface velocities are due to basal sliding in the fast-flowing glacier tongue (>1 km a−1). We force the model using different surface mass-balance scenarios taken or adapted from previous studies and geodetic elevation changes between 2000 and 2012. Our results suggest that previous estimates of average surface mass balance over the entire glacier (Ḃ) were likely too high, mainly due to an overestimation in the accumulation area. We propose that most of SRG imbalance is due to the large ice discharge (−0.83 ± 0.08 Gt a−1) and a slightly positiveḂ(0.08 ± 0.06 Gt a−1). The committed mass-loss estimate over the next century is −0.34 ± 0.03 Gt a−1. This study demonstrates that surface mass-balance estimates and glacier wastage projections can be improved using a physically based ice flow model.

Highlights

Patagonia is the largest ice-covered region in the Southern Hemisphere outside of Antarctica (Rignot and others, 2003)
In the steep zones where we find large relative velocity errors, the inverse method produces large basal shear stresses (>200 kPa) and the sliding velocity is nearly zero showing that the error cannot be reduced by controlling the friction only
Our results show that this new methodology is appropriate to independently constrain surface mass balance and ice discharge from fast-moving glaciers where ice dynamics are significant

Summary

Introduction

Patagonia is the largest ice-covered region in the Southern Hemisphere outside of Antarctica (Rignot and others, 2003). Most of the ice is locked in two main icefields: the Northern Patagonia Icefield (NPI 3976 km2) and the Southern Patagonia Icefield (SPI 13219 km2) (Davies and Glasser, 2012). The NPI is located between 46.5°S and 47.5°S It is under the influence of the westerlies (Garreaud and others, 2009) and climate settings are largely influenced by the Southern Annular Mode (Thompson and Wallace, 2000; Garreaud and others, 2013). This elevation band comprises a flat and vast plateau, making the icefield surface mass balance sensitive to shifts in the ELA in response to changes in temperature and accumulation. A recent ice velocity mosaic reveals that fast flow regions extend far into the plateau and accumulation area, making the icefield potentially sensitive to dynamical changes (Mouginot and Rignot, 2015)

Methods

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Discussion

Conclusion