Revisiting the impact of the Drake Passage opening on ocean circulation and Eocene climate - A model study with paleo-friendly conditions
Résumé
The impact of the Drake Passage (DP) opening on climate is being debated for dozens of years. Indeed, being one of
the major geographical changes occurring during the Eocene and at the beginning of a global climate cooling, it has
often generated a lot of interest. To date, even though the overall signal remains unclear, it is considered as one of
the main potential cause of the contemporaneous climate change. Several model studies have been aiming to assess
the importance of this gateway opening through different more or less complex models. However, according to our
knowledge on palaeoenvironments, most of them considered unrealistic boundary conditions (notably a low pCO2
or a today-like geography) that might corrupt the transposition of their results to the original deep-time context. In
order to better understand if and how climate might have been affected by this gateway opening the DP question
is 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 performed
using 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 Current
and effects on temperatures remain geographically constrained. These experiments should help to understand if
the impact of the DP was progressive or rather non linear while the passage deepened. Our results are compared to
Neodymium and d13C data and discussed in the broader context of the Eocene-Oligocene climatic transition.