||GRACE Secular Trend, Mantle Viscosity Regimes and Uncertainty in Southern Hemispheric Glacial Isostatic Modeling
Ice core data now provide a record of the Antarctic climate spanning the past 330,000 years. This data, along with the wealth of other new information that constrain past ice mass history throughout the Southern Hemisphere, implies that far more reliable glacioisostatic models may be built for predicting geodetic change parameters, such as bedrock motions, low degree zonal coefficient change and geoid change patterns that might be detected by GRACE.
Present-day ice mass change in West Antarctica is potentially detectable by GRACE. The present-day signature may be clearly separated from the glacial isostatic adjustment (GIA) signal across a fairly broad spectrum of viscosity regimes. Only at the rheologically weakest part of this spectrum does some ambiguity arise. (Appropriate uplift data on bedrock would remove this ambiguity.)
A new ice model is constructed for Antarctica that is consistent with dated moraines, exposure dating, grounding line migration, numerical modeling and newly emerging uplift data. Except in the weakest rheological regime, the model peak predicts uplift rates of 8-25 mm/yr in West Antarctica and rates in East Antarctica that are bound by -1.5 to +4.0 mm/yr. The corresponding geoid rate due to GIA is upper bounded by 1.0 mm/yr. Secular ice mass loss in Antarctica, if sustained at 70 Gt/yr (roughly equivalent to a 0.2 mm/yr sea level rise contribution), produces geoid rate signals with five times the strength of GIA, but at much higher spherical harmonic degree and order. The uncertainty of the ice model for times prior to the Antarctic Cold Reversal (14-12.5 kyr BP), and the corresponding implication for GRACE and extended mission data analysis, are explored and discussed.