Constraining the recent mass balance of Pine Island and Thwaites glaciers, West Antarctica, with airborne observations of snow accumulation

B Medley,J T M Lenaerts,S Gogineni,E J Steig,J P Nicolas,J R Mcconnell,S B Das,I Joughin,B E Smith,H Conway,C Lewis,A S Criscitiello,M R Van Den Broeke,C Leuschen,D H Bromwich

doi:10.5194/tc-8-1375-2014

Abstract

Abstract. In Antarctica, uncertainties in mass input and output translate directly into uncertainty in glacier mass balance and thus in sea level impact. While remotely sensed observations of ice velocity and thickness over the major outlet glaciers have improved our understanding of ice loss to the ocean, snow accumulation over the vast Antarctic interior remains largely unmeasured. Here, we show that an airborne radar system, combined with ice-core glaciochemical analysis, provide the means necessary to measure the accumulation rate at the catchment-scale along the Amundsen Sea coast of West Antarctica. We used along-track radar-derived accumulation to generate a 1985–2009 average accumulation grid that resolves moderate- to large-scale features (>25 km) over the Pine Island–Thwaites glacier drainage system. Comparisons with estimates from atmospheric models and gridded climatologies generally show our results as having less accumulation in the lower-elevation coastal zone but greater accumulation in the interior. Ice discharge, measured over discrete time intervals between 1994 and 2012, combined with our catchment-wide accumulation rates provide an 18-year mass balance history for the sector. While Thwaites Glacier lost the most ice in the mid-1990s, Pine Island Glacier's losses increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sea-level rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008.

Highlights

Pine Island (PIG) and Thwaites (THW) glaciers are two of the largest Antarctic contributors to recent sea-level rise (SLR) (Rignot et al, 2008; Shepherd et al, 2012) and will likely continue contributing substantially over the century (Joughin et al, 2010; Gladstone et al, 2012)
While the minimum error in each catchment is the same (0.01 m w.e. yr−1), the maximum is much greater within the Pine Island catchment (0.17 m w.e. yr−1) than over that of Thwaites (0.04 m w.e. yr−1), which is due to the larger accumulation rates and associated bias correction on Pine Island glacier
We find that a well-designed accumulation radar survey combined with glaciochemical analysis of one or more well-sited firn cores is sufficient to generate a catchment-wide accumulation map that resolves moderate- to large-scale features

Summary

Introduction

Pine Island (PIG) and Thwaites (THW) glaciers are two of the largest Antarctic contributors to recent sea-level rise (SLR) (Rignot et al, 2008; Shepherd et al, 2012) and will likely continue contributing substantially over the century (Joughin et al, 2010; Gladstone et al, 2012). Sensed measurements of ice-surface velocity over the past few decades revealed that the rate of ice discharge from Pine Island and Thwaites glaciers is increasing (Rignot, 2001, 2008; Joughin et al, 2003), resulting in extensive thinning near their margins (Thomas et al, 2004; Pritchard et al, 2009) This rapid dynamical change is likely the consequence of warm ocean currents melting and thinning the buttressing ice shelves, an effect observed over much of West Antarctica (Shepherd et al, 2004; Joughin et al, 2012; Pritchard et al, 2012; Rignot et al, 2013; Depoorter et al, 2013). While our understanding of the dynamics of these glaciers has improved substantially over the past decade, snow accumulation over large areas of these glaciers has only been sparsely sampled (van de Berg et al, 2006) limiting a complete understanding of their overall mass change

Results

Discussion

Conclusion