Timing of Recent Accelerations of Pine Island Glacier, Antarctica

Abstract

We have used Interferometric Synthetic Aperture Radar (InSAR) data and sequential Landsat imagery to identify and temporally constrain two acceleration events on Pine Island Glacier (PIG). These two events are separated by a period of at least seven years (1987–1994). The change in discharge between two flux gates indicates that the majority of the increase in discharge associated with the second acceleration originates well inland (>80 km) from the grounding line. An analysis indicates that changes in driving stress consistent with observed thinning rates are sufficient in magnitude to explain much of the acceleration.

Sustained retreat of the Pine Island Glacier

“…However, an extrapolation of the recent PIG volume trend acceleration [Wingham et al, 2009] provides a much smaller estimated contribution of around 2 cm by the year 2100-a value that is consistent with the 1.8 cm likely estimate of a basin-scale model of the glacier response to ocean forcing [Joughin et al, 2010]. Moreover, although changes occurring in the vicinity of the PIG grounding line are expected to cause thinning inland for decades to come [Payne et al, 2004;Joughin et al, 2003], and the presence of an extended region of lightly grounded ice at the glacier terminus has promoted rapid retreat in recent years , the glacier and bedrock geometry farther inland impedes further retreat in numerical simulations-even allowing for an increase in ocean melting [Joughin et al, 2010]. Here we use satellite radar interferometry and satellite radar altimetry to analyze the rate of hinge-line retreat and thinning to establish whether the glacier has reached this anticipated state of relative stability.…”

“…It is also possible that ocean melting has exceeded that imposed during existing simulations. The progressive retreat of the PIG hinge line has occurred presumably as a result of changes in both the rate of ocean melting and the glacier surface slope, the latter occurring as a dynamical response to reduced grounding [Joughin et al, 2003;Payne et al, 2004]. Although a substantial bedrock peak occurs around 25 km inland of the present hinge-line position (Figure 3d), this feature does not straddle the entire glacier width [Vaughan et al, 2006], and relief to the south side of the glacier, in particular, slopes gently.…”

“…Satellite observations show that glaciers draining this sector are retreating [Rignot, 1998b], thinning [Shepherd et al, 2001;Shepherd et al, 2002;Shepherd and Peacock, 2003], accelerating [Joughin et al, 2003], and losing mass [Rignot, 2008]. Observations of ice shelf thinning in the face of increased glacier discharge and a numerical simulation of glacier response to external forcing [Payne et al, 2004] suggest that the surrounding ocean is the source of this imbalance.…”

Understanding and Modelling Rapid Dynamic Changes of Tidewater Outlet Glaciers: Issues and Implications

“…The acceleration at the terminus increases the ice flux and initiates a thinning, which steepens the surface, increases the driving stress and leads to further acceleration. Through this feedback between acceleration and driving-stress the thinning is then propagating upstream with time (Payne et al 2004;Joughin et al 2003Joughin et al , 2008c. This thinning is a direct consequence of mass conservation and readjusts the flux back towards the preperturbation state in order to compensate for the mass loss.…”

Representing Grounding Line Dynamics in Numerical Ice Sheet Models: Recent Advances and Outlook

“…Pine Island (PIG) and Thwaites Glaciers, situated in the Amundsen Sea Embayment, are the main contributors to this WAIS mass loss (Shepherd et al 2001). PIG in particular has shown a nearly continuous acceleration (Joughin et al 2003) and thinning (Wingham et al 2009) during recent years. Recent evidence shows that this thinning is due to an inland grounding line migration from the 1970s to present by 30 km (Jenkins et al 2010).…”