Mass gains of the Antarctic ice sheet exceed losses

Abstract

During 2003 to 2008, the mass gain of the Antarctic ice sheet from snow accumulation exceeded the mass loss from ice discharge by 49 Gtlyr (2.5% of input), as derived from ICESat laser measurements of elevation change. The net gain (86 Gtlyr) over the West Antarctic (WA) and East Antarctic ice sheets (W A and EA) is essentially unchanged from revised results for 1992 to 2001 from ERS radar altimetry. Imbalances in individual drainage systems (DS) are large (-68% to +103% of input), as are temporal changes (-39% to +44%). The recent 90 Gtlyr loss from three DS (Pine Island, Thwaites-Smith, and Marie-Bryd Coast) of WA exceeds the earlier 61 Gtlyr loss, consistent with reports of accelerating ice flow and dynamic thinning. Similarly, the recent 24 Gtlyr loss from three DS in the Antarctic Peninsula (AP) is consistent with glacier accelerations following breakup of the Larsen B and other ice shelves. In contrast, net increases in the five other DS ofWA and AP and three of the 16 DS in East Antarctica (EA) exceed the increased losses. Alternate interpretations of the mass changes driven by accumulation variations are given using results from atmospheric-model re-analysis and a parameterization based on 5% change in accumulation per degree of observed surface temperature change. A slow increase in snowfall with climate wanning, consistent with model predictions, may be offsetting increased dynamic losses.

Comment on Zwally and others (2015)-Mass gains of the Antarctic ice sheet exceed losses

“…In the light of the hydrostatic balance, the significant spatial variation in height change rates across the lake area in Figure 5 of Zwally and others (2015), e.g. the jumps in ICESat profile 0330 and slopes in profiles 1312 and 0077, need further explanation.…”

“…height a −1 ) using measured densities. It is therefore inappropriate to choose an arbitrary density value to reconstruct the snow build-up rate from published accumulation rates, as exercised by Zwally and others (2015) in their attempt to invalidate the conclusion of a stable surface height from Richter and others (2008). The density value of 0.33 g cm −3 adopted by Richter andothers (2008, 2014) represents the best estimate for the surface snow layer combining the results from numerous snow pits and measurements in the Vostok accumulation stake farm (Ekaykin and others, 2003;personal communication from Ekaykin, 2007).…”

“…First, the accumulation map derived by Arthern and others (2006) and evoked by Zwally and others (2015) has already been reported to overestimate the accumulation rates in the Vostok Subglacial Lake region by ∼10 mm w.e. a −1 (i.e.…”

“…In particular, it would require an implausibly large local anomaly in ice-thickness change close to Vostok station to counterbalance a mean ice-thickness growth of 2 cm a −1 implied by the remote sensing results as interpreted by Zwally and others (2015).…”

“…In their article 'Mass gains of the Antarctic ice sheet exceed losses ' Zwally and others (2015) choose Vostok Subglacial Lake as an exemplary region to demonstrate their inference of surface height change rates from a portion of the ICESat mission's laser altimetry data . In their appendix, they discuss some of the remarkable differences between their results and those reported by Richter and others (2008Richter and others ( , 2013Richter and others ( , 2014.…”