Responses of planktonic foraminifera to the emergence of the Isthmus of Panama

Abstract

Pliocene-Pleistocene planktonic foraminiferal assemblages of the Esmeraldas section in northwestern Ecuador and of Hole 1039B off Costa Rica are analyzed. In the Esmeraldas section, an abrupt cooling of the sea-water temperature is recognized between 3.35 and 3.95 Ma, in which Neogloboquadrina spp. and intermediate water dwellers increase in abundance. In the section off Costa Rica, the sea-water temperature declined just before 4.2 Ma, when planktonic foraminifera become absent, but increased afterwards as evidenced by abundant occurrences in Zone N22 to the Recent. These faunal changes are considered to be responses to the emergence of the Isthmus of Panama.