Climate and Ocean Circulation at the Paleocene/Eocene Boundary and Their Sensitivity to Atmospheric CO2

We study the climate at the Paleocene/Eocene (PE) boundary (55 Ma) using the coupled AO-GCM ECHAM5/MPI- OM. Applying simple PE boundary conditions and a CO2 concentration of 560ppm already yields a very warm, sea-ice free climate. Still, the Pole-Equator SST gradient is higher than suggested by proxy data. The simulated ocean circulation in the Atlantic is characterized by deepwater formation in the Proto-Labrador Sea. This North Atlantic Deepwater (NADW) flows southward as a western boundary current below the depth of the open Panama Strait. For a CO2 concentration of only 280ppm, the NADW formation becomes even stronger and deeper. By contrast, Nunes and Norris (2006) inferred a northward Atlantic bottom water track for the period before the Paleocene/Eocene Thermal Maximum from d13C gradients. The Pacific Meridional Overturning Circulation for a CO2 concentration of 560ppm is quite weak. Yet for the reduced atmospheric CO2 concentration of 280ppm, strong southern deepwater formation occurs.