Predictions of Antarctic crustal motions driven by present‐day ice sheet evolution and by isostatic memory of the Last Glacial Maximum

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Abstract
Detectable crustal motion and secular rate of change of solid‐surface gravity may be produced by the Earth's response to present‐day and past ice mass changes in Antarctica. Scenarios of present‐day ice mass balance, previously utilized to explore the global geodetic signatures of the Antarctic ice sheet, produce elastic crustal responses that are typically bounded by uplift rates ≤5 mm/yr, horizontal motion ≤1 mm/yr, and solid‐surface gravity change rates ≤1 μGal/yr. In a restricted locality, 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 Glacial Maximum (LGM) exceeds 5 mm/yr (uplift) over substantial portions of West Antarctica for a wide range of plausible choices of timing and magnitude of deglaciation and mantle viscosity. Similarly, viscoelastic gravity rate predictions exceed 1 μGal/yr (decrease) over large regions, confirming suggestions that a Global Positioning System (GPS) and absolute gravity‐based program of crustal monitoring in Antarctica could potentially detect postglacial rebound. A published revision to the CLIMAP model of the Antarctic ice sheet at LGM, herein called the D91 model, features a substantially altered West Antarctic ice sheet reconstruction. This revision predicts a spatial pattern of present‐day crustal motion and surface gravity change that diverges strikingly from CLIMAP‐based models. Peak D91 crustal rates, assuming deglaciation begins at 12 kyr and ends at 5 kyr, are around 16 mm/yr (uplift), 2 mm/yr (horizontal), and −2.5 μGal/yr (gravity). Tabulated crustal response predictions for selected Antarctic bedrock sites indicate critical localities in the interior of West Antarctica where expected responses 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 contribution to sea level rise over the past 20,000 years.