Simulating and Investigating the 100ka ice age cycle with a three dimensional ice sheet model and GCM.

One of the challenges of earth system modelling is to confirm the theories of ice age cycle by simulating the realistic response of the climate system to the change of orbital parameters, known as Milankovitch forcing, by phisically based models instead of conceptual models. Here we simulate the ice age cycle and investigate the origin of 100ka cycle using a three dimensional ice sheet model which includes the thermo-mechanical coupling (verified by the simulation of Antarctica and Greenland ice sheet) with the process of isostatic rebound. We also use an atmospheric GCM (CCSR/NIES) coupled to a slab ocean to estimate the climate sensitivity to Milankovitch forcing and atmospheric CO2 indicated by ice core data. Within the range of possibilities of the physically based model, ice age cycles with a sawtooth shape 100 ka cycle and the major NH ice sheet (Laurentide ice sheet and FennoScandian ice sheet) volume and geographical distribution in the past 400,000 years are successfully simulated. It is shown that both contribution of CO2 and Milankovitch forcing are necessary for the ice age cycle, although the CO2 change affects the global climate change. The effect of orbital forcings, long-term CO2 change, response time of crustal rebound and continental distribution upon the origin of 100 ka cycle will be investigated and discussed.