We apply geologic evidence from ice-free areas in
Antarctica to evaluate model simulations of ice sheet response to warm
climates. This is important because such simulations are used to predict ice
sheet behaviour in future warm climates, but geologic evidence of
smaller-than-present past ice sheets is buried under the present ice sheet
and therefore generally unavailable for model benchmarking. We leverage an
alternative accessible geologic dataset for this purpose: cosmogenic-nuclide
concentrations in bedrock surfaces of interior nunataks. These data produce
a frequency distribution of ice thickness over multimillion-year periods,
which is also simulated by ice sheet modelling. End-member transient models,
parameterized with strong and weak marine ice sheet instability processes
and ocean temperature forcings, simulate large and small sea-level impacts
during warm periods and also predict contrasting and distinct frequency
distributions of ice thickness. We identify regions of Antarctica where
predicted frequency distributions reveal differences in end-member ice sheet
behaviour. We then demonstrate that a single comprehensive dataset from one bedrock
site in West Antarctica is sufficiently detailed to show that the data are
consistent only with a weak marine ice sheet instability end-member, but
other less extensive datasets are insufficient and/or ambiguous. Finally, we
highlight locations where collecting additional data could constrain the
amplitude of past and therefore future response to warm climates.</p