Modeling the dynamic response of outlet glaciers to observed ice-shelf thinning in the Bellingshausen Sea Sector, West Antarctica

Brent M Minchew,Helen A Fricker,Fernando S Paolo,G Hilmar Gudmundsson,Alex S Gardner

doi:10.1017/jog.2018.24

Abstract

ABSTRACTSatellite observations of gravity anomalies, ice-surface elevation and glacier velocity show significant increases in net grounded-ice-mass loss over the past decade along the Bellingshausen Sea sector (BSS), West Antarctica, in areas where warm (>1°C) sea water floods the continental shelf. These observations provide compelling but indirect evidence that mass losses are driven primarily by reduced buttressing from the floating ice shelves caused by ocean-driven ice-shelf thinning. Here, we combine recent observations of ice velocity, thickness and thickness changes with an ice flow model to study the instantaneous dynamic response of BSS outlet glaciers to observed ice-shelf thinning, alone. Our model results show that multiple BSS outlet glaciers respond instantaneously to observed ice-shelf thinning, particularly in areas where ice shelves ground at discrete points. Increases in modeled and observed dynamic mass losses, however, account for ~5% of the mass loss rates estimated from gravity anomalies and changes in ice-surface elevation, suggesting that variations in surface mass balance may be key to understanding recent BSS mass loss. Our approach isolates the impact of ice-shelf thinning on glacier flow and shows that if ice-shelf thinning continues at or above current rates, total BSS mass loss will increase in the next decade.

Highlights

Reliable projections of ice-sheet mass loss and subsequent changes in sea level require understanding the relative contributions of the processes that couple ice sheets, oceans and climate (Favier and others, 2014; Alley and others, 2015; DeConto and Pollard, 2016)
We focus on the Bellingshausen Sea sector (BSS), a region in West Antarctica that contains numerous outlet glaciers (Fig. 1a) that flow into buttressing ice shelves that are both confined along their margins and contain numerous pinning points (Fürst and others, 2016)
Our results show that perturbations in ice-shelf thickness induce instantaneous increases in ice velocities and dynamic thinning rates, both of which broadly agree with observed magnitudes and spatial patterns near (

Summary

INTRODUCTION

Reliable projections of ice-sheet mass loss and subsequent changes in sea level require understanding the relative contributions of the processes that couple ice sheets, oceans and climate (Favier and others, 2014; Alley and others, 2015; DeConto and Pollard, 2016). Ice shelves, when confined along their margins or grounded at discrete points along their bases (pinning points), resist the seaward flow of ice and thereby influence the rate of ice discharge to the ocean (Thomas, 1979; Gudmundsson, 2013; Kowal and others, 2016). This buttressing effect is sensitive to changes in local ocean temperature because warmer seawater tends to melt, and thin ice shelves, which can reduce buttressing and increase glacier velocities (Jenkins and Jacobs, 2008; Holland and others, 2010; Mouginot and others, 2014; Seroussi and others, 2014). We use recent observations of ice surface velocity and ice-shelf thinning rates along with an ice flow model to quantify the dynamic response of BSS outlet glaciers to ice-shelf thinning

Surface velocity observations

Numerical model

Ice-shelf thickness perturbations

Glacier acceleration and mass loss

Projections of dynamically driven mass loss

CONCLUSION