Various modeling studies have examined the climatic effects of either the Central American Seaway or the Indonesian seaway. The co‐existence of these two tropical seaways may have a greater influence than the existence of a single seaway. Although the dual seaway situation is closer to that reconstructed during Miocene/Pliocene, relevant studies remain scarce. Here, we investigate the co‐effects of dual tropical seaway changes on the Pacific circulation through a set of sensitivity experiments. Our results show that the combined shallow opening of tropical seaways can generate an active Pacific meridional overturning circulation and maintain strong upwelling conditions along the equatorial Pacific, which may have helped favor a “biogenic bloom” during the late Miocene and early Pliocene. Moreover, the logically successive closure of the tropical seaways can provide patterns of zonal sea surface temperature gradients that are similar to those recorded in the equatorial Pacific from the late Miocene to the Pliocene.

Several regional climates during the Eocene are still under debate, and the Eocene environment of China is a particular focus of the discussion. One view, based on the widely distributed pollen of Ephedripites, as well as red beds and evaporite sediments, suggests that a dry zonal belt (Figure 1a) dominated mid-latitude China from west to east (Guo et al., 2002,;Sun & Wang, 2005;Wang, 1990). To the north and the south of the arid zonal belt, humid climates appeared in Northeast and South China, where pollen assemblages indicative of humid conditions, as well as coal and oil shales, occur in Eocene sediments (