Mass balance reassessment of glaciers draining into the Abbot and Getz Ice Shelves of West Antarctica

Abstract

We present a reassessment of input‐output method ice mass budget estimates for the Abbot and Getz regions of West Antarctica using CryoSat‐2‐derived ice thickness estimates. The mass budget is 8 ± 6 Gt yr−1 and 5 ± 17 Gt yr−1 for the Abbot and Getz sectors, respectively, for the period 2006–2008. Over the Abbot region, our results resolve a previous discrepancy with elevation rates from altimetry, due to a previous 30% overestimation of ice thickness. For the Getz sector, our results are at the more positive bound of estimates from other techniques. Grounding line velocity increases up to 20% between 2007 and 2014 alongside mean elevation rates of −0.67 ± 0.13 m yr−1 between 2010 and 2013 indicate the onset of a dynamic thinning signal. Mean snowfall trends of −0.33 m yr−1 water equivalent since 2006 indicate recent mass trends are driven by both ice dynamics and surface processes.

Increased West Antarctic and unchanged East Antarctic ice discharge over the last 7 years

“…Glaciers feeding the Getz and Sulzberger ice shelves (B20; including Berry, Hull and Land glaciers) increased in speed by 10 to 100 m yr −1 at their grounding lines, increasing discharge by 6 % (Table 2). This result is in broad agreement with Chuter et al (2017) that observed increases in ice velocity during the 2007-2013 period alongside 2010-2013 dynamic thinning rates of 0.7 m yr −1 for the glaciers feeding the Abbot and Getz ice shelves.…”

“…10), summing to a total imbalance of −214 ± 51 Gt yr −1 with largest rates of loss collocated with increased glacier velocities along the Amundsen Sea Embayment (B21 and B22) and Getz Ice Shelf (B20). The large mass loss for the Getz Ice Shelf region is in contrast to the near balance conditions recently reported by Chuter et al (2017) for the 2006-2008 period but is in agreement with the 2010-2013 estimate of net mass change by Martín-Español et al (2016). The East Antarctic Ice Sheet is found to have increased slightly in mass at a rate of 61 ± 73 Gt yr −1 with largest gains in Dronning Maud (B6) and Enderby Land (B7 and B8) that can be partially attributed to increase in precipitation rate (+28 Gt yr −1 relative to 1979-2007 mean) during the study period, which is consistent with earlier findings (Boening et al, 2012;Shepherd et al, 2012).…”

“…Even so, the dynamic volume change correction is very small and insensitive to the selected cutoff velocity. Calculation of discharge is highly sensitive to the definition of the flux gate and to any vertical gradient in the ice flow (Chuter et al, 2017;Mouginot et al, 2014;Rignot, 2006;Rignot and Thomas, 2002). When calculating ice flux, we assume that there are no vertical gradients in ice velocity.…”

“…Since surface velocities are always larger than the depthaveraged velocity this introduced a positive bias into our estimates of ice flux. Neglecting sliding and assuming a depth constant creep parameter (A) the depth-averaged velocity is 80 % of the surface velocity (Cuffey and Paterson, 2010). Assuming parallel flow and a linear increase in shear stress with depth, the surface velocity due to creep (V s ) can be calculated as follows:…”

“…n is typically assumed to be 3 and so is done here. t b is calculated using the surface slope and ice depth (Cuffey and Paterson, 2010). The creep parameter A (Fig.…”