Quantifying the role of geographic change in Cenozoic ocean heat transportusing uncoupled atmosphere and ocean models

A series of five Cenozoic atmospheric general circulation model (ACCM) expe riments has been performed using a new set of paleogeographic reconstructio ns for 55. 40, 33, 20 and 14 Ma. The five continental reconstructions incor porate the tectonic evolution of early Eocene to middle Miocene continental positions and topography. With all other model boundary conditions and for cings held constant, the series of AGCM experiments captures a < 1 degrees C decrease in annual mean temperature through the Paleogene and early Neoge ne. Regional and seasonal differences among the five experiments are small in magnitude, but are consistent with the imposed paleogeographic changes. From the AGCM experiments alone, it might be concluded that changes in cont inental positions had little impact on Cenozoic climate change. However, oc ean configuration changes between 55 and 14 Ma, especially gateway openings and closures, are expected to produce significant changes in ocean thermoh aline circulation, a system that cannot be simulated by the slab ocean mode l component of an AGCM. The nature of changes in ocean heat transport and t hermohaline circulation arising from the evolution of early Eocene through middle Miocene ocean basin configurations is examined in a series of five g lobal, three-dimensional ocean model experiments forced by output from the AGCM. The ocean model suggests that paleogeographic change throughout the C enozoic has caused changes in the interhemispheric partitioning of heat tra nsport and that the modern shape of the ocean heat transport curve has evol ved in response to ocean basin evolution. The prediction of very low ocean heat transport in the Northern Hemisphere of the early and middle Eocene su ggests a much more important role for atmospheric heat transport in the tem perate polar climates of the Eocene than is generally acknowledged. Results suggest that Southern Hemisphere ocean heat transport decreased throughout the interval 55-14 Ma. The results also show that, in the absence of relia ble coupled models for paleoclimate studies, Full three-dimensional ocean m odels must be used in parallel with slab ocean AGCMs if we wish to understa nd the true effects of paleogeographic change on climate and the true natur e of past ocean heat transport. (C) 2000 Elsevier Science B.V. All rights r eserved.