Ensemble simulation of the MIS 12-MIS 11 glacial cycle using a fully coupled climate-ice sheet model

The Marine Isotope Stage (MIS) 12-MIS 11 glacial cycle (490-396 Ka) has been recognized as anomalous by researchers due to the longevity of the interglacial interval.  MIS 12 sea level low stand is inferred to be similar to Last Glacial Maximum (LGM), however, due to limited geomorphological data, major uncertainties remain with respect to where the ice was distributed and the relative size of the ice sheets. With the lowest increase in insolation from glacial to interglacial of the past 800 kyrs, MIS 11 was almost twice as long as the other interglacials of the past 500 kyrs. A prevailing hypothesis for the duration of MIS 11 proposes that the large MIS 12 ice sheets, when exposed to a weak insolation increase, gradually released meltwater and deglaciated throughout the interglacial period, contributing to its extended duration. This freshwater influx triggered a positive feedback, promoting the release of oceanic CO₂ into the atmosphere, which amplified insolation-driven warming and further prolonged the interglacial period.

Given the lack of terrestrial paleoclimate data, ice and climate modelling may offer a way to improve the understanding of this curious interval. Previous modeling work of this interval has been with either highly parameterized, low-resolution coupled ice-climate models, climate models with forced ice sheets, snapshot climate models with pre-industrial ice sheets, or ice sheet models with forced climate. Few models span the entire duration of the glacial cycle. For the first time, we transiently simulate the entire interval with the fully coupled ice sheet-climate LCIce model that resolves both atmospheric and ocean circulation. Parametric uncertainties are addressed by ensemble simulation. This presentation focuses on ensemble analysis of the ice sheets and climate of the glacial cycle as well as sensitivity testing of the two hypothesized drivers for length of MIS 11: meltwater flux during deglaciation and atmospheric CO₂ concentration.