Past climate and the role of ocean heat transport: Model simulations for the Cretaceous

A series of general circulation model experiments using Global Environmental and Ecological Simulation of Interactive Systems (GENESIS) were executed to evaluate the sensitivity of simulated mid‐Cretaceous climate to small perturbations in ocean heat transport. Three experiments were performed: (1) mixed layer ocean with no ocean heat transport, ZEROQ, (2) ocean heat transport specified as required for GENESIS to best match modern observations, ONEQ, and (3) doubled ocean heat transport, TWOQ. The ONEQ experiment represents an ocean heat transport which is actually about 15% of the values given by Carissimo et al. (1985) from modern observations. As a sensitivity experiment these model simulations represent a doubling of the role of the ocean. However, relative to the observations, they represent small perturbations to the total poleward heat transport in the model. With the exception of the tropics, no major changes in the structure of the general circulation of the atmosphere resulted from the modification of the ocean heat transport. However, relatively small increases in ocean heat transport resulted in a number of significant differences between simulations, including tropical cooling, polar warming, weakened equator‐to‐pole surface temperature gradients, weakened midlatitude jets, decreased land‐sea pressure contrast, and decreased midlatitude storminess. The experiments indicate that changes in ocean heat transport which are well within the realm of possibility for Earth history can have significant climatic impact. Although ocean heat transport may be a significant factor in explaining Cretaceous polar warmth, the changes specified in these experiments alone are not sufficient to explain the polar warmth of the Cretaceous.