Eocene - Oligocene paleobathymetry of the Atlantic - Arctic Oceanic Gateways: Influence on ocean circulation and climate

The Eocene-Oligocene boundary (~ 34 Ma) marks a turning point in the transition from a warm greenhouse climate to a cold icehouse climate in the Cenozoic time (66 – 0 Ma). Around this boundary, geological evidence shows the first signs of ice sheets on Antarctica, and evidence of ice-rafted debris offshore East Greenland. Topographic changes, especially the opening and closing of strategic oceanic gateways, have been proposed as triggers for this climate cooling. 

We have developed a new global paleobathymetry/topography model for the Eocene-Oligocene boundary with focus on the Northern hemisphere oceanic gateways and implemented our reconstruction in the Norwegian Earth System Model (NorESM-F). Our new topography model shows that changes in these gateways also occurred around this time, especially in the NE Atlantic Ocean and the Tethys Seaway. To test the importance of these gateways and their combined effects we create a set of model simulations by changing the paleobathymetric configurations of the most important oceanic gateways (i.e. the Greenland – Scotland Ridge, Fram Strait, Southen Ocean gateways and the Tethys Seaway). All the scenarios are detailed realistic reconstructions within the error of our paleobathymetry/topography model. The model shows that the depth of the Greenland-Scotland ridge controls the freshwater input to the North Atlantic and opening the gateway leads to large Northern hemispheric cooling as the freshwater reduces ocean convection and the Atlantic overturning circulation slows down. On the other hand, opening the Southern Ocean gateways facilitates the flow of the Antarctic Circumpolar Current and leads to expected cooling in Antarctica. Based on our model results we suggest that bathymetric changes around the Eocene - Oligocene boundary were important in initiating the cooling which was then enhanced by feedbacks in the Earth System.​