| I will present a new global ice-sheet reconstruction for the last
deglaciation. Unlike other global deglacial chronologies, GLAC-1b
includes a posterior distribution of deglacial chronologies (currently
for the three largest ice sheets) relative to observational
constraints. As such, confidence intervals can be defined. The
Eurasian and North American components are from recently completed
Bayesian calibrations of the 3D MUN glacial systems model (GSM), while
the Antarctic component is from an initial scored ensemble of 2929
runs with the MUN/PSU GSM. Both versions of the GSM include
thermo-mechanically coupled glaciological ice-sheet models,
visco-elastic bedrock response with the VM5a earth rheology, various
climate representations, and a range of components to enable
comparison of model output against observational records. The
calibration and scoring is against a diverse and large set of
constraint data, include relative sea level (RSL), marine limits,
strandline elevations, present day rates of uplift, and the current
configuration of the Antarctic ice sheet. The Greenland chronology is
from an earlier glaciological model hand-tuned against RSL data.
An ongoing issue is an apparent shortfall of at least 10 m eustatic
sea-level equivalent when model results are compared against far-field
RSL datasets. Such a shortfall is not new. An examination of the
evolution of past geophysically-constrained global deglacial ice sheet
and ice load reconstructions will reveal a reliance of sticking extra
ice where there's no data in order to fit far-field constraints. As
new data has arisen, this extra ice load as been sequentially shifted
to new regions. I will describe the key observational and physical
constraints that limit continental ice volumes in GLAC-1b, and finish
with a few ideas of how this shortfall may be resolved. |