Lower satellite-gravimetry estimates of Antarctic sea-level contribution

Abstract

Recent estimates of Antarctica's present-day rate of ice-mass contribution to changes in sea level range from 31 gigatonnes a year (Gt yr(-1); ref. 1) to 246 Gt yr(-1) (ref. 2), a range that cannot be reconciled within formal errors. Time-varying rates of mass loss contribute to this, but substantial technique-specific systematic errors also exist. In particular, estimates of secular ice-mass change derived from Gravity Recovery and Climate Experiment (GRACE) satellite data are dominated by significant uncertainty in the accuracy of models of mass change due to glacial isostatic adjustment (GIA). Here we adopt a new model of GIA, developed from geological constraints, which produces GIA rates systematically lower than those of previous models, and an improved fit to independent uplift data. After applying the model to 99 months (from August 2002 to December 2010) of GRACE data, we estimate a continent-wide ice-mass change of -69 ± 18 Gt yr(-1) (+0.19 ± 0.05 mm yr(-1) sea-level equivalent). This is about a third to a half of the most recently published GRACE estimates, which cover a similar time period but are based on older GIA models. Plausible GIA model uncertainties, and errors relating to removing longitudinal GRACE artefacts ('destriping'), confine our estimate to the range -126 Gt yr(-1) to -29 Gt yr(-1) (0.08-0.35 mm yr(-1) sea-level equivalent). We resolve 26 independent drainage basins and find that Antarctic mass loss, and its acceleration, is concentrated in basins along the Amundsen Sea coast. Outside this region, we find that West Antarctica is nearly in balance and that East Antarctica is gaining substantial mass.

Secular changes in Earth’s shape and surface mass loading derived from combinations of reprocessed global GPS networks

“…Shepherd et al (2012) also inspected the Greenland ice sheet and estimated a mass loss of −142 ± 49 Gt/years which broadly matches our result. Comparing our results to recent work by King et al (2012) who, using GRACE data and updated GIA models, present new evidence for a significantly reduced estimate of mass loss from Antarctica may suggest that our dismissal of the Peninsula results is overly cautious. Work presented by Shepherd et al (2012) also suggests a reduced value for the Antarctic Peninsula.…”

Observations: Cryosphere

“…The first, by King et al (2012), notes recent estimates of Antarctic ice-mass change cannot be reconciled with each other within the cited formal errors. They cite inadequacy in the models of glacial isostatic adjustment (GIA) as a major cause and adopt a new GIA model with better geological constraints.…”

“…Current GIA calculations for ice sheets are confounded by, among other things, an effect that creates an erroneous conclusion of ice loss when in reality there has been an ice increase (Irvin and James, 2005;Shum et al, 2008;Tegoning et al, 2009;King et al, 2012).…”

“…Until an adequate TRF has been established, papers that use GRACE data, including recent reviews of ice-sheet mass balance like those of King et al (2012) and Shepherd et al (2012), must be viewed as speculative "best interpretations" of the available, noisy data. However, and noting Earth has no intrinsic or "preferred" long-term ice mass balance (as discussed in Section 5.8.1), the fact that as yet we have no way of accurately measuring ice sheet dynamics does not lessen the intrinsic interest of studying historic and modelled changes in the planetary ice budget through time.…”

Sedimentary and structural evolution of a relict subglacial to subaerial drainage system and its hydrogeological implications: an example from Anglesey, north Wales, UK

“…Understanding the behaviour of subglacial meltwater systems is crucial because of their influence upon substrate rheology and ice-bed coupling (Boulton & Hindmarsh, 1987;Iverson et al, 1995;Boulton, 1996;Piotrowski et al, 2004Piotrowski et al, , 2006Evans et al, 2006;Kjaer et al, 2006;Lee & Phillips, 2008;Boulton et al, 2009), and in-turn, glacier dynamics that operate over a range of temporal and spatial scales (Kamb, 1987;Bartholomew et al, 2010;Sundal et al, 2011;Robel et al, 2013). Research now recognises that these processes act to drive the expansion, break-up and collapse of major ice streams and ice masses (MacAyeal, 1993;Clark, 1994;Tulaczyk et al, 2000;Bell et al, 2007;Stokes et al, 2007;Burke et al, 2012) thus linking subglacial drainage to collapsing ice masses, sea-level change and abrupt climate change (Goezler et al, 2011;King et al, 2012;Hanna et al, 2013;Fürst et al, 2014 and references therein). Indeed, subglacial meltwater systems underpin major global issues surrounding the stability of the modern Antarctic and Greenland ice sheets, their sensitivity too and influence on current and future changes in sea-level and climate (Alley et al, 2005;Zwally et al, 2005;Shepherd & Wingham, 2007;Pfeffer et al, 2008).…”