The Global Meridional Overturning Circulation of the Paleozoic Ocean

  The global meridional overturning circulation (GMOC) plays an important role in transporting oceanic heat from one hemisphere to the other. At present, the AMOC descends in the North Atlantic and is responsible for transporting large amount of heat from the Southern Hemisphere (SH) to the Northern Hemisphere (NH). In the early Paleozoic, the continental configuration was nearly opposite to that of the present, with most of the landmass located in the SH and an ocean world of the NH. Here, we present simulation results to demonstrate that the GMOC in the Paleozoic was anticlockwise, with upwelling in the NH and descending in the SH, which is opposite to that of the present. The anticlockwise GMOC in the Paleozoic is mainly due to hemispheric asymmetry of wind stresses and freshwater input into the ocean. Stronger wind stress in the NH drives upwelling in the NH extratropics. Less freshwater input into the SH ocean causes saltier and heavier seawater, which is conducive to deep water formation in the SH ocean. These hemispheric asymmetries of wind stresses and freshwater are because of land-sea distribution in the Paleozoic. Two datasets are used, which show consistent results in general.