NSFGEO-NERC:The Collapse of the Cordilleran Ice Sheet: Using Glacial Dipsticks to Constrain Ice Sheet Modeling

Projections of future sea level rise rely on ice sheet models that are highly tuned to simulate the geometry and flow of the modern ice sheets despite uncertainties in the surface mass balance and unknown basal processes. Overfitting these models to the present day means that the sensitivity of the ice sheet to future warming is untested and unconstrained.

Recent advances in cosmogenic dating (a method to measure how long glacially eroded rocks have been exposed to the sun) as well as ice sheet modeling and statistical uncertainty quantification now make it feasible to use reconstructions of past ice sheet changes to test and improve coupled climate-ice sheet models. While many ice sheets have been reconstructed with great detail, the deglaciation of the Cordilleran Ice Sheet that covered the Rocky Mountains in North America during the last ice age is poorly constrained.

Yet, this ice sheet offers great potential to constrain models due to its similarities to modern ice sheets, such as the southern Greenland Ice Sheet (mountainous, high accumulation and strong precipitation gradients, marine/land terminating). The Cordilleran Ice Sheet is also thought to have played a key role in rapid sea level and climate changes during the last deglaciation (a transition 21-7 thousand years ago that took us out of the last ice age), but evidence of this is limited.

Our team of researchers, with a proven track record in reconstructing and modeling deglacial ice sheets and climate, will produce the first 3-D reconstruction of Cordilleran Ice Sheet collapse during the last deglaciation based on a robust empirical-modeling approach. We will undertake a carefully designed field campaign across this large and mountainous region to apply the "glacial dipstick" approach, generating 135 Be-10 ages along ~15 vertical transects.

Using a statistical Uncertainty Quantification approach, we will combine the field data with modeling of the Cordilleran and western Laurentide Ice Sheets with a complex yet efficient coupled climate-ice sheet model used for future projections. This will produce an ensemble of plausible reconstructions for the deglaciation of the Cordilleran Ice Sheet.