Sensitivity of mid-Miocene simulations to different continental configurations

The Langhian (15.98 - 13.82 Ma) was a stage of the mid-Miocene characterized by higher atmospheric CO2 concentrations than modern days and substantially warmer surface temperatures. The mid-Miocene has garnered growing attention as a potential analog for future climate change. Several climate models have assessed the influence of CO2 and geography on the Miocene warmth. In this study, we simulated the Langhian using a new unpublished paleogeography. This configuration notably features shallower and narrower access to the Arctic Ocean than has been previously documented. Despite CO2 concentrations equivalent to three times the pre-industrial levels (840 ppm) and the absence of ice sheets, we observe persistent sea ice in the Arctic Ocean and cooling of the Northern Atlantic Ocean. This cooling is related to the collapse of the Atlantic meridional ocean circulation. Conversely, a robust Pacific meridional ocean circulation emerges, which is less frequently observed in Miocene simulations. We investigate the reasons behind such behavior, by notably widening and deepening the Fram Strait; forcing a fixed, warmer vegetation; using a more recent atmospheric model with improvement to the physics. These adjustments underscore the critical role of geography in achieving an accurate simulation of the Miocene and facilitating more precise data-model comparisons.