February 28, 2007
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FROM VOLUME 9, NUMBER 5, MAY 1996
EARTH SYSTEM SCIENCE: ICE SHEET STABILITY
Two related items in Science 271(5052), Feb. 9, 1996:
"Rapid Collapse of Northern Larsen Ice Shelf, Antarctica," H. Rott
(Inst. Meteor., Univ. Innsbruck, Innrain 52, A-6020 Innsbruck, Austria), P.
Skvarca, T. Nagler, 788-792. Documents the January 1995 breakup of 4200 square
kilometers of the ice shelf, based on radar images from the ERS-1 satellite and
field observations. The nearly complete disintegration of the ice occurred
within a few days, following a period of steady retreat that coincided with a
regional trend of atmospheric warming. The observations imply that after an ice
shelf retreats beyond a certain limit, it may collapse as a result of altered
"An Ice Shelf Breakup," M. Fahnestock (Ctr. for Earth System Sci.,
Univ. Maryland, College Pk. MD 20742), 775-776. Discusses the difficulties of
interpreting the results of the previous paper in the context of climatic
trends. The breakup of the Larson ice shelf did not directly influence sea level
because it was already floating, but it may be a signal of changing conditions
on the Antarctic peninsula.
"Recent Atmospheric Warming and Retreat of Ice Shelves on the
Antarctic Peninsula," D.G. Vaughan (British Antarctic Survey, Natural
Environ. Res. Council, Madingley Rd., Cambridge CB3 0ET, UK), C.S.M. Doake, Nature,
379(6563), 328-331, Jan. 25, 1996.
Compares the 50-year trend of the areal extent of nine ice shelves to
meteorological records. The five northerly ones have retreated dramatically in
the past 50 years, consistent with the existence of an abrupt thermal limit on
ice-shelf viability, the location of which has drifted southward. Ice shelves
therefore appear to be sensitive indicators of climate change. The authors
cannot determine whether this Antarctic Peninsula warming is related to a global
warming, or is a natural oscillation.
"Pliocene-Pleistocene Diatoms in Paleozoic and Mesozoic Sedimentary
and Igneous Rocks from Antarctica: A Sirius Problem Solved," L.H. Burckle
(Lamont-Doherty Earth Observ., Rte. 9W, Palisades NY 10964), N. Potter Jr., Geology,
24(3), 235-238, Mar. 1996.
The 1984 discovery of fossilized oceanic plants (diatoms) in the Sirius
Group sedimentary rocks of the Transantarctic Mountains sparked a debate on the
stability of the East Antarctic ice sheet, suggesting that the sheet may have
melted in the past, and could do so in the future. However, geological evidence
presented in this paper is consistent with an alternative theorythat the
diatoms were blown there by wind.
"Behavior of the East Antarctic Ice Sheet as Deduced from a Coupled
GCM/Ice Sheet Model," M. Verbitsky (Dept. Geol., Yale Univ., New Haven CT
06520), B. Saltzman, Geophys. Res. Lett., 22(21), 2913-2916,
Nov. 1, 1995.
The possible instability of the West Antarctic ice sheet has been widely
recognized for some time as a potential source of sea-level rise in an enhanced
greenhouse warming, but only recently has the East Antarctic ice sheet been the
subject of such a conjecture. Model results given here show little chance of
collapse from changes in normal glacial creep and topographic instabilities. But
the mechanics of basal sliding, non-isothermal effects, and ice shelves are as
yet too poorly understood to make quantitative estimates of possible
instabilities related to these processes.
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