Both surface and deep sea waters warmed, even near Antarctica. Deep circulation remains sluggish. High percentage of the plant species had smooth margins . Equatorial zones were largely covered by oceans, allowing more absorption of solar heat. Less area covered by snow and ice, more exposed land, allowing more absorption of solar heat Presence of dense forests at high latitudes.
Forests have low albedo, trap heat and moisture.
Intense volcanism at mid-ocean ridge associated with opening of North Atlantic may have released greenhouse gases. Poleward flow of warm saline waters at intermediate depth. Because of the near freezing temperatures and intense pressure, methane released by bacteria on the deep seafloor is locked up inside linked water molecules to form ice. After Early Eocene, three steps of global cooling. Fossil Flora Record Fossil plants provide a record of dramatic cooling of Earth's climate after the early Eocene interval of global warmth.