Revisiting the impact of the Drake Passage opening on ocean circulation and Eocene climate - A model study with paleo-friendly conditions

International audienceThe impact of the Drake Passage (DP) opening on climate is being debated for dozens of years. Indeed, being one ofthe major geographical changes occurring during the Eocene and at the beginning of a global climate cooling, it hasoften generated a lot of interest. To date, even though the overall signal remains unclear, it is considered as one ofthe main potential cause of the contemporaneous climate change. Several model studies have been aiming to assessthe importance of this gateway opening through different more or less complex models. However, according to ourknowledge on palaeoenvironments, most of them considered unrealistic boundary conditions (notably a low pCO2or a today-like geography) that might corrupt the transposition of their results to the original deep-time context. Inorder to better understand if and how climate might have been affected by this gateway opening the DP questionis here evaluated using an up2date IPCC like model, the IPSL-CM5A2, and Eocene-friendly boundary conditions(1120ppm, 40Ma land-sea distribution including an open Panama Seaway). Four simulations have been performedusing a closed Drake configuration and different DP depths 100m, 300m and 1000m. Striking changes are visible,since the earliest changes of the gateway opening, in the oceans dynamics and the Southern Ocean properties.However, the Drake throughflow remains weak, by far less intense than a mature Antarctic Circumpolar Currentand effects on temperatures remain geographically constrained. These experiments should help to understand ifthe impact of the DP was progressive or rather non linear while the passage deepened. Our results are compared toNeodymium and d13C data and discussed in the broader context of the Eocene-Oligocene climatic transition