A new glacial isostatic adjustment model for Antarctica: calibrated and tested using observations of relative sea-level change and present-day uplift rates
2012
We present a glacial isostatic adjustment (GIA) model for Antarctica. This is driven by a
new deglaciation history that has been developed using a numerical ice-sheet model, and is
constrained to fit observations of past ice extent. We test the sensitivity of the GIA model to
uncertainties in the deglaciation history, and seek earth model parameters that minimize the
misfit of model predictions to relative sea-level observations from Antarctica. We find that
the relative sea-level predictions are fairly insensitive to changes in lithospheric thickness and
lower mantle viscosity, but show high sensitivity to changes in upper mantle viscosity and
constrain this value (95 per cent confidence) to lie in the range 0.8–2.0 × 10 21 Pa s. Significant
misfits at several sites may be due to errors in the deglaciation history, or unmodelled effects of
lateral variations in Earth structure. When we compare our GIA model predictions with elastic corrected
GPS uplift rates we find that the predicted rates are biased high (weighted mean
bias = 1.8mm yr –1 ) and there is a weighted root-mean-square (WRMS) error of 2.9mm yr –1 .
In particular, our model systematically over-predicts uplift rates in the Antarctica Peninsula,
and we attempt to address this by adjusting the Late Holocene loading history in this region,
within the bounds of uncertainty of the deglaciation model. Using this adjusted model the
weighted mean bias improves from 1.8 to 1.2mm yr –1 , and the WRMS error is reduced to
2.3mm yr –1 , compared with 4.9mm yr –1 for ICE-5G v1.2 and 5.0mm yr –1 for IJ05. Finally,
we place spatially variable error bars on our GIA uplift rate predictions, taking into account
uncertainties in both the deglaciation history and modelled Earth viscosity structure. This
work provides a new GIA correction for the GRACE data in Antarctica, thus permitting more
accurate constraints to be placed on current ice-mass change.
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