Sea-level feedback lowers projections of future Antarctic Ice-Sheet mass loss

Abstract

The stability of marine sectors of the Antarctic Ice Sheet (AIS) in a warming climate has been identified as the largest source of uncertainty in projections of future sea-level rise. Sea-level fall near the grounding line of a retreating marine ice sheet has a stabilizing influence on the ice sheets, and previous studies have established the importance of this feedback on ice age AIS evolution. Here we use a coupled ice sheet–sea-level model to investigate the impact of the feedback mechanism on future AIS retreat over centennial and millennial timescales for a range of emission scenarios. We show that the combination of bedrock uplift and sea-surface drop associated with ice-sheet retreat significantly reduces AIS mass loss relative to a simulation without these effects included. Sensitivity analyses show that the stabilization tends to be greatest for lower emission scenarios and Earth models characterized by a thin elastic lithosphere and low-viscosity upper mantle, as is the case for West Antarctica.

Large ensemble modeling of the last deglacial retreat of the West Antarctic Ice Sheet: comparison of simple and advanced statistical techniques

“…The best-fit range for the asthenospheric relaxation timescale TAUAST values is quite broad, including the prior reference value ∼ 3 kyr but extending to shorter times ∼ 1 kyr. This may be connected with low upper-mantle viscosities and thin crustal thicknesses suggested in recent work (Whitehouse et al, 2012b;Chaput et al, 2014), which will be examined in further work with full Earth models (Gomez et al, 2013(Gomez et al, , 2015Konrad et al, 2015).…”

“…Based on more sophisticated global Earth models, the asthenospheric e-folding timescale is commonly set to 3 kyr (e.g., Gomez et al, 2013), but note that recent geophysical studies suggest considerably shorter timescales for some West Antarctic regions (Whitehouse et al, 2012b;Chaput et al, 2014). In further work we plan to perform large ensembles with the icesheet model coupled to a full Earth model, extending Gomez et al (2013Gomez et al ( , 2015.…”

Glacial Isostatic Adjustment modelling: historical perspectives, recent advances, and future directions

“…Furthermore, models that consider the coupled evolution of the ice sheet-solid Earth system (see Sect. 3.1) will be highly sensitive to the underlying viscosity field (Gomez et al, 2015b;Konrad et al, 2015;Pollard et al, 2017).…”

“…It is interesting to note that LGM reconstructions for Antarctica generated using coupled models tend to contain 1-2 m less ice (expressed as sea-level 555 equivalent) than reconstructions generated using uncoupled models (de Boer et al, 2017). If the coupled model results are robust this makes it difficult to account for the global mean sea-level lowstand during the LGM (Clark and Tarasov, 2014 Considering future ice-sheet change, Adhikari et al (2014) have used one-way coupling to quantify the impact of ongoing GIA on Antarctic ice dynamics up to 2500 AD, while Gomez et al (2015b) and Konrad et al (2015) have used coupled 560 models to investigate the long-term evolution of the ice sheet, finding that GIA-related feedbacks have the potential to significantly limit, or even halt, future ice loss if the upper mantle viscosity beneath West Antarctica is low enough for rapid rebound to be triggered. A crucial factor in determining the stability of an ice sheet is the resistance provided by the surrounding floating ice shelves.…”

Progress in Numerical Modeling of Antarctic Ice-Sheet Dynamics

“…Gravitationally self-consistent sea-level models incorporating Maxwell viscoelastic deformation of the solid Earth have recently been coupled to ice-sheet models to investigate their effect on millennial time scales [19,62] as its importance for the stability of the West-Antarctic ice sheet on these time scales has been demonstrated [74]. However, given the thin elastic lithosphere and low-viscosity upper mantle in West Antarctica, this effect may even be important on centennial time scales [63].…”