GLAC3 rates and phasing: the first joint history matching of global last glacial cycle ice sheet evolution and regional earth rheology

GLAC3 is the first history matching of every last glacial cycle ice sheet. It therefore includes North American, Greenlandic, Icelandic,Eurasian, Tibetan, Patagonian, and Antarctic components. Instead of determining a non-robust "optimal" chronology, history matching aimsto "bound reality" with robust assessment of both proxy data and model (both parametric and structural) uncertainties. For the four major icesheets, this entails Bayesian artificial neural network emulation of the glaciological model predictions to enable adequate Markov ChainMonte Carlo sampling of chronologies. The history matching is against a large set of geophysical (such as relative sea level and marinelimit), geological (cosmogenic exposure and C14 ages), and glaciological (such as present-day ice surface velocity) constraints.Aside from being a product of history matching, GLAC3 has two additional unique features. Firstly, it is the only availabledeglacial, let alone full glacial cycle, global set of chronologies from glaciological modelling, using the Glacial Systems Model(GSM) with hybrid shallow ice and shallow shelf ice dynamic. This enables physical resolution of ice sheets, ice streams, ice shelves,and grounding line migration. As such, GLAC3 is subject to glaciological constraints such as borehole temperature profiles thatnon-glaciological reconstructions can't resolve. Secondly, the glaciologically modelling is self-consistently coupled with fullvisco-elastic glacio-isostatic adjustment enabling joint history matching of ice history and regional earth viscosity.The presentation will focus on the relative phasing of each ice sheet, rates of mass gain and loss, and rates of ice margin migration. Thiswill be compared against both far-field relative sea level records as well as the results of fully coupled ice and climate modelling of thelast glacial cycle with LCice (LOVECLIM + GSM).