Is the west Antarctic Ice Sheet disintegrating?

Abstract

Data pertaining to the dynamics and history of the west antarctic ice cover are reviewed and interpreted in terms of a possible inherent instability of the ice cover. A study of published data concerning the past and present ice cover of West Antarctica indicates that during the last few million years the ice sheet has been retreating in stages, each retreat stage being preceded by an advance of comparable duration. Thus disintegration of the west antarctic ice sheet seems to follow the disintegration pattern of other continental ice sheets and may be the last phase of the worldwide Late Cenozoic ice age. At least some of the retreat stages seem to have been rapid enough to be called surges. Stages of advance seem to have temporarily introduced equilibrium conditions, since equilibrium ice sheet surface profiles can be reconstructed from the moraines, etc., and thus mark the stable limits of each advance. Present ice sheet surface profiles along flowlines entering both the Ronne and the Ross ice shelves from Marie Byrd Land are not equilibrium profiles, suggesting that the west antarctic ice sheet is unstable. An analysis of the grounded portion of the west antarctic ice cover indicates that data relating to the surface profile, ice velocity, and the mass balance are all incompatible with an equilibrium ice sheet. Instability seems to be centered in the major ice streams that drain Marie Byrd Land. An analysis of the floating portion of the west antarctic ice cover indicates that basal melting is most pronounced along the Siple Coast of the Ross ice shelf and causes retreat of the grounding line into Marie Byrd Land. Instability seems to be related to sudden retreats of the grounding line.