PREDICTIONS OF ANTARCTIC CRUSTAL MOTIONS DRIVEN BY PRESENT-DAY ICE-SHEET EVOLUTION AND BY ISOSTATIC MEMORY OF THE LAST GLACIAL MAXIMUM

Detectable crustal motion and secular rate of change of solid-surface gravity may be produced by the Earth's response to present-day and pas t ice mass changes in Antarctica. Scenarios of present-day ice mass ba lance, previously utilized to explore the global geodetic signatures o f the Antarctic ice sheet, produce elastic crustal responses that are typically bounded by uplift rates less than or equal to 5 mm/yr, horiz ontal motion less than or equal to 1 mm/yr, and solid-surface gravity change rates less than or equal to 1 mu Gal/yr. In a restricted locali ty, one scenario produces uplift rates slightly in excess of 10 mm/yr and correspondingly enhanced horizontal and gravity rates. In contrast , the viscoelastic response to ice mass changes occurring since Last G lacial Maximum (LGM) exceeds 5 mm/yr (uplift) over substantial portion s of West Antarctica for a wide range of plausible choices of timing a nd magnitude of deglaciation and mantle viscosity. Similarly, viscoela stic gravity rate predictions exceed 1 mu Gal/yr (decrease) over large regions, confirming suggestions that a Global Positioning System (GPS ) and absolute gravity-based program of crustal monitoring in Antarcti ca could potentially detect postglacial rebound. A published revision to the CLIMAP model of the Antarctic ice sheet at LGM, herein called t he D91 model, features a substantially altered West Antarctic, ice she et reconstruction. This revision predicts a spatial pattern of present -day crustal motion and surface gravity change that diverges strikingl y from CLIMAP-based models. Peak D91 crustal rates, assuming deglaciat ion begins at 12 kyr and ends at 5 kyr, are around 16 mm/yr (uplift), 2 mm/yr (horizontal), and -2.5 mu Gal/yr(gravity). Tabulated crustal r esponse predictions for selected Antarctic bedrock sites indicate crit ical localities in the interior of West Antarctica where expected resp onses are large and D91 predictions differ from CLIMAP-based models by a factor of 2 or more. Observations of the postglacial rebound signal in Antarctica might help constrain Antarctic mass balance and contrib ution to sea level rise over the past 20,000 years.