Heat transport, deep waters, and thermal gradients: Coupled simulation of an Eocene Greenhouse Climate

For the first time, a coupled general circulation model with interactive an d dynamical atmospheric, oceanic, and sea-ice components, is used to simula te an Eocene (similar to 50 Ma) "greenhouse" climate. We introduce efficien t ocean spin-up methods for coupled paleoclimate modeling. Sea surface temp eratures (SSTs) and salinities evolve unconstrained, producing the first pr oxy data-independent estimates for these Eocene climate parameters. Tropica l and extratropical model-predicted SSTs are warmer than modern values, by 3 and 5 degreesC, respectively. Salinity-driven deep water formation occurs in the North Atlantic and Tethys. The zonal average overturning circulatio n is weaker than modern. Eocene ocean heat transport is 0.6 PW less than mo dern in the Northern Hemisphere and 0.4 PW greater in the Southern Hemisphe re. The model-predicted near-modern vertical and meridional Eocene temperat ure gradients imply that the dominant theory for maintaining low gradients- increased ocean heat transport-is incorrect or incomplete and other mechani sms should be explored.