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Abstract

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.

Item Type:	Article
Authors/Creators:	King, MA and Coleman, R and Morgan, PJ and Hurd, R
Keywords:	Amery Ice Shelf; multidecadal; slowdown.
Journal or Publication Title:	Journal of Geophysical Research Earth Surface
Publisher:	American Geophysical Union
ISSN:	0148-0227
DOI / ID Number:	https://doi.org/10.1029/2006JF000609
Additional Information:	Copyright 2007 by the American Geophysical Union.
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