GLAC3: Joint glaciological model and visco-elastic earth model history matching of the last glacial cycle: Greenland and Antarctica components

We present the Antarctic and Greenland components of an extensive
history matching for last glacial cycle evolution and regional earth
rheology from glaciological modelling with fully coupled regional
visco-elastic glacio-isostatic adjustment.  Of further distinction is
the accounting for model structural uncertainty. The product is a high
variance set of joint chronologies and earth model parameter vectors
that are not inconsistent with available constraints given
observational and model uncertainties.

Ensemble parameters are from Markov Chain Monte Carlo sampling with
Bayesian artificial neural network emulators.  The glaciological model
is the Glacial Systems Model with hybrid shallow shelf and shallow ice
physics and a coupled energy balance climate model. It includes a much
larger set of ensemble parameters (34 and 38 respectively for
Greenland and Antarctica) than other paleo ice sheet models to
facilitate more complete assessment of past ice sheet evolution
uncertainty. The history matching is against a large curated set of
relative sealevel, vertical velocity, cosmogenic age, and marine
constraints as well as the present-day physical and thermal
configuration of the ice sheet.

The careful assessment of uncertainties, breadth of modelled
processes, and sampling approach has resulted in NROY (not ruled out
yet) chronologies and rheological inferences that contradict previous
more limited model-based reconstructions.  For instance, in contrast
to most previous inferences for the Antarctic contribution to the last
glacial maximum (LGM) low-stand (with inferred values of about 10 m ice
equivalent sea-level (mESL), our NROY set includes chronologies with
LGM contributions of up to 23 mESL.  This result represents a
potentially significant contribution towards addressing the challenge
of LGM missing ice.