A comparative study of the Paleocene and Eocene assemblages of benthic foraminifers from the northwestern and southern Pacific Ocean allowed us to establish a series of regularities probably reflecting their response to paleoceanological changes. The gradual penetration of warmer near-bottom waters enriched in nutrients might result in the growth of the abundance and diversity of the assemblages, while the entrance of cold poor waters leads to a decrease in these parameters. The leveling of the differences in the species composition of the assemblages from the northern and southern Pacific Ocean over the Paleogene was probably caused by the gradual transformation of the near-bottom Pacific waters due to tectonic and oceanological processes. By the end of the Paleogene, these processes finally resulted in the formation of a psychrosphere in the ocean characterized by uniform hydrological characteristics of the near-bottom waters.