Velocity change of the Amery Ice Shelf, East Antarctica, during the period 1968–1999

Abstract

[1] Historic velocity measurements of Antarctica's ice sheet represent vital baseline values that allow ice flow velocity variations to be observed over multidecadal timescales, such as those due to climate change. Using velocity values derived from geodetic quality measurements made in the 1960s and from more recent GPS and remote sensing studies during the 1990s, we examine the variability of ice flow velocities of the northern Amery Ice Shelf, East Antarctica, over the 30-year period, 1968-1999. The historic ice shelf velocities are reexamined using original field notes and the previous data analyses are shown to be erroneous, yielding positional and velocity errors of up to 4 km and 150 m/yr respectively. Once corrected, these historic measurements are shown to be in close (1-5 m/yr) general agreement with GPS-derived velocities from the 1990s at similar geographical locations, providing one of the first precise constraints on multidecadal ice shelf velocity variations on a large Antarctic ice shelf. Comparison of the terrestrial and GPS velocities with spatially dense velocity measurements from remote sensing imagery reveals a systematic bias in the latter of up to ±30 m/yr, mostly due to propagation of unmodeled vertical ice shelf motion due to tides and atmospheric pressure variations. We therefore excluded the remote sensing velocities from further comparison and suggest caution in the interpretation of similarly derived ice shelf velocities. Velocity differences between the GPS and terrestrial surveys were compared at nine geographical locations suggesting a small ($2.2 m/yr or $0.6%), but statistically significant, slowdown of the ice shelf.

A 4‐decade record of elevation change of the Amery Ice Shelf, East Antarctica

“…Our finding that the central AIS has not undergone substantial net surface elevation change over ∼39 years is consistent with the velocity change analysis of King et al [2007] who concluded that the central AIS had undergone only a very small reduction in ice velocity over the period 1968–1999. Simple considerations of force balance in the ice shelf suggest that a regionally slightly thinner ice shelf would be consistent with slightly lower velocities.…”

“…Zwally et al [2005], for example, used ERS Radar Altimetry (RA) to show that many Antarctic ice shelves increased or decreased in elevation with typical rates of ±(0.1 -0.4) ma 1 over the period 1992-2001. [ 4 ]T he Amery Ice Shelf (AIS), East Antarctica (Figure 1), has along record of elevation measurements, acquired using various methods between 1968 and 2007. The first geodetic quality optical leveling profiles were obtained in late 1968 in conjunction with observations used to generate precise velocity and strain data [ Budd et al,1 982;King et al, 2007]. More than 500 km of the central AIS was surveyed along three profiles (two transverse and one longitudinal to the ice flow direction).…”

Mass Balance Assessment of the Amery Ice Shelf Basin, East Antarctica

“…The negligible ice discharge change between 2000 and 2016 indicates the relatively stable dynamics of the AIS basin in recent decades. In fact, previous studies (King et al, 2007;Tong et al, 2018) have shown that the ice velocity in the AIS hardly changed in the past 45 years . An investigation of decade-scale ice-shelf thickness changes has also shown that the overall thickness change of the AIS is 1.6 ± 1.1 m per decade, which is close to zero (Paolo et al, 2015).…”

A DORIS determination of the absolute velocities of the Sorsdal and Mellor glaciers in Antarctica

“…King et al (2007) established that a geographically correlated bias of between ±8 and 11 cm/day existed between the InSAR velocities of Joughin (2002) and Young and Hyland (2002) in comparison to the Terrestrial/GPS determined velocities in the AIS. Although this study was confined to the northern AIS, the identified error sources contributing to this bias, in particular the measured slant ranges, can be considered to be common to the entire RADARSAT solution.…”