The paleoclimate was also derived from continental drift and plate tectonic theories in that paleocurrent and paleocirculation varied according to the location of the continents. Throughout most of geologic time continents have been arranged so that equatorial currents flow freely around the earth. Equatorial current is heated more because much of it circulates around the Earth more than once.
North and south flowing currents that diverge from equatorial currents are warmer.
The Ordovician is considered to have been warmer than the current climate. Since Laurentia was equatorial, the water masses were warm and thus had a relatively low density. They were of lower salinity than other oceanic water due to high precipitation in the tropics which also contributed to lower density.
The primary cause for surface circulation of the ocean is wind blowing over water.