Influence of ocean tides on the general ocean circulation in the early Eocene

The early Eocene (∼56-50 million years ago) was characterized by higher surface temperatures and a reduced meridional temperature gradient, compared to present-day conditions. The origin of the decreased meridional temperature gradient is still subject to discussion and might be linked to tides. Tidal mixing could have enhanced the meridional heat transport and thereby decreased the meridional temperature gradient. We test this hypothesis by simultaneously modelling tidal dynamics and the general ocean circulation for the early Eocene in a new coupled atmosphere-ocean model setup. We find an interaction between tidal currents and the ocean general circulation that increases horizontal velocities in 25% of the deep ocean to more than 400% of its original value. The global meridional overturning circulation (GMOC) is strengthened thereby locally by 60-100%. However, the oceanic meridional heat transport is only increased by a maximum of 0.1PW (8%) and a mean of less than 0.018PW (5.1%), thus not decreasing the meridional temperature gradient considerably.