Evidence Against and Factors Preventing Major Surges of the Antarctic Ice Sheet

Abstract

AbstractAlthough computer modelling using realistic flow parameters can simulate surging of the Antarctic ice sheet, the present model does not take into account certain factors that make surging less probable. Before discussing these factors, knowledge of the Antarctic ice sheet that might indicate the occurrence of former surging is reviewed. The following studies appear relevant (a)Observed temperature–depth profiles approximate to steady-state solutions, whereas a major surge within the last 10 000 to 20000 years would have produced markedly different temperature–depth profiles at Byrd and Vostok Stations.(b)Isotopic profiles are estimated for steady-state and for surging behaviour of the Antarctic ice sheet. When these are compared with observed profiles no convincing evidence of surging over the past 10 000 to 50 000 years is seen.(c)Studies of flow lines in and around the Ross Ice Shelf do not reveal any surging of discharge glaciers in the past I 000 to 2 000 years.(d)Although mass-balance calculations and balance-velocity calculations on the Antarctic ice sheet are not accurate, ice discharge is generally estimated to be within a factor of two of the total mass accumulation.Three stabilizing factors that have not been included in computer models and need consideration are (1)It appears unlikely that a surge will be propagated up-stream of any substantial bedrock slope that opposes the ice motion.(2)The very high effective viscosity of great thicknesses of ice at very low temperatures adds considerable rigidity to the ice sheet at the lateral boundaries of any incipient surge.(3)Strong convergence of flow lines towards ice streams and major trunk glaciers apparently provides a stabilizing factor.