A comparison of the last two glacial inceptions (MIS 7/5) via fully coupled transient ice and climate modeling

Abstract. Little is known about the evolution of continental ice sheets through the last two glacial inceptions (Marine isotope stages, MIS 7d and MIS 5d). Here, we present the results of a perturbed parameter ensemble of transient simulations of the last two glacial inceptions and subsequent interstadials (MIS 7e-7c, 240–215 ka and MIS 5e-5c, 122–98 ka) with the fully coupled ice/climate model LCice. LCice includes all critical direct feedbacks between climate and ice. As shown herein, it can capture the inferred sea level change (of up to 80 m) of the last two glacial inceptions within proxy uncertainty. One key underlying question of paleoclimate dynamics is the non-linear state dependence of the climate system. Concretely, in a model-centric context, to what extent does the capture of one climate interval in an Earth systems model guarantee capture of another interval? For LCice, the capture of present-day climate is insufficient to predict capture of glacial inception climate, as only a small fraction of ensemble members that performed "well" for present-day captured inception. Furthermore, the capture of inferred sea level change in one inception has weak correlation with the same outcome for the other.

After partial history matching against present-day and past sea level constraints, the resultant NROY (not ruled out yet) ensemble of simulations have a number of features of potential interest to various paleo communities, including the following. (i) In correspondence with the inferred last glacial maximum configuration, the simulated North American ice sheets are substantially larger than the Eurasian ice sheet throughout MIS 5d-MIS 5c and MIS 7d-MIS 7c. (ii) Hudson Bay can transition from an ice-free state to full ice cover (grounded ice) within 2000 years. (iii) The North American and Eurasian ice sheets advanced southward with rates well above 100 m/yr during the penultimate glacial inception and over 70 (Eurasia) and 90 (North America) m/kyr during last glacial inception. (iv) the Laurentide and Cordilleran ice sheets merge in their northern sectors in 13 out of 14 NROY simulations for MIS 7d, contrary to what is assumed from limited geological data. (v) larger ice sheets display a larger lag in the timing of stadial maximum ice volume compared to that of the insolation minimum; the North American ice sheet maximum lags 5.3 ± 0.5 kyrs behind the MIS 7d insolation minimum. Supplemental resources include a dynamic display of ice advance and subsequent retreat for a sub-ensemble of 14 NROY simulations from MIS 5d-5c and MIS 7d-7c.