Miocene evolution of atmospheric carbon dioxide

Changes in pCO(2) or ocean circulation are generally invoked to explain warm early Miocene climates and a rapid East Antarctic ice sheet (EAIS) expansion in the middle Miocene. This study reconstructs late Oligocene to late Miocene pCO(2) from epsilon(p) values based on carbon isotopic analyses of diunsaturated alkenones and planktonic foraminifera from Deep Sea Drilling Project sites 588 and 608 and Ocean Drilling Program site 730. Our results indicate that highest pCO(2) occurred during the latest Oligocene (similar to 350 ppmv) but decreased rapidly at similar to 25 Ma. The early and middle Miocene was characterized by low pCO(2) (260-190 ppmv), Lower intervals of pCO(2) correspond to inferred organic carbon burial events and glacial episodes with the lowest concentrations occurring during the middle Miocene, There is no evidence for either high pCO(2) during the late early Miocene climatic optimum or a sharp pCO(2) decrease associated with EAIS growth. Paradoxically, pCO(2) increased following EAIS growth and obtained preindustrial levels by similar to 10 Ma. Although we emphasize an oceanographic control on Miocene climate, low pCO(2) could have primed the climate system to respond sensitively to changes in heat and vapor transport.